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Curry, O. S., Rowland, L., Zlotowitz, S., McAlaney, J., & Whitehouse, H. (submitted). Happy to Help? A systematic review and meta-analysis of the effects of performing acts of kindness on the well-being of the actor. Psychological Bulletin.

Working Paper

Curry, O. S., Rowland, L., Zlotowitz, S., McAlaney, J., & Whitehouse, H. (submitted). Happy to Help? A systematic review and meta-analysis of the effects of performing acts of kindness on the well-being of the actor. Psychological Bulletin.

HAPPY TO HELP
Happy to Help? A systematic review and meta-analysis of the effects of performing acts of
kindness on the well-being of the actor
Oliver Scott Curry
University of Oxford
Lee Rowland
University of Bournemouth
Sally Zlotowitz
University College London
John McAlaney
University of Bournemouth
Harvey Whitehouse
University of Oxford
Author Note
Oliver Scott Curry, Institute of Cognitive and Evolutionary Anthropology, University of
Oxford; Lee Rowland, Department of Psychology, University of Bournemouth; Sally Zlotowitz,
Department of Clinical Educational and Health Psychology, University College London; John
McAlaney, Department of Psychology, University of Bournemouth; Harvey Whitehouse,
Institute of Cognitive and Evolutionary Anthropology, University of Oxford
This work on this article was supported by kindness.org. Thanks to Caspar van Lissa and
Rongqin Yu for statistical advice, to Rosalind Arden for useful discussions, to Helena Cronin for
comments on the manuscript, and to Steve Rowland and Emma Seymour for research assistance.
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Title page with All Author Information
HAPPY TO HELP
Correspondence concerning this article should be addressed to Oliver Scott Curry,
Institute of Cognitive and Evolutionary Anthropology, University of Oxford, 64 Banbury Road,
Oxford, OX2 6PN.!
E-mail: oliver.curry@anthro.ox.ac.uk
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Abstract
Does being kind make you happy? Recent advances in the behavioural sciences have provided a
number of explanations of human social, cooperative and altruistic behaviour. These theories
predict that people will be ‘happy to help’ family, friends, community members, spouses, and
even strangers under some conditions. As a preliminary test of whether and to what extent these
predictions are supported by the existing literature, here we conduct a systematic review and
meta-analysis of the experimental evidence that kindness interventions (for example, performing
’random acts of kindness’) boost subjective well-being. Our initial search of the literature
identifies 428 articles; of which 19 (21 studies) meet the inclusion criteria (total N=2,685). We
find that the overall effect of kindness on well-being is small-to-medium (d = 0.38). There is also
some indication of publication bias – lower quality studies tended to find larger effects –
suggesting that the true effect size may be smaller still (0.31 d 0.34). We also find that the
design and methodological limitations of existing studies preclude the testing of specific theories
of kindness. We recommend that future research: distinguish between the effects of kindness to
specific categories of people (for example, family, friends, strangers); take kindness-specific
individual differences into account; and consider a wider range of distal outcome measures. Such
research will advance our understanding of the causes and consequences of kindness, and help
practitioners to maximise the effectiveness of kindness interventions.
Keywords: kindness, altruism, happiness, well-being, positive psychology!
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HAPPY TO HELP
Happy to Help? A systematic review and meta-analysis of the effects of performing acts of
kindness on the well-being of the actor
Does being kind make you happy? Does doing good make you feel good? Over the past
few decades, advances in the evolutionary behavioural sciences have developed numerous
theories of human social, cooperative and altruistic behaviour. These theories — kin altruism,
mutualism, reciprocal altruism, and competitive altruism — make it possible to explain a variety
of different ‘kinds of kindness’ (for example, love, sympathy, gratitude and heroism). And they
predict that people will be ‘happy to help’ family, friends, community members, spouses, and
even strangers under some conditions.
More recently, there has been growing interest in using kindness as an intervention to
boost ‘subjective well-being’ (including happiness, life-satisfaction and positive affect). It has
been argued that altruism — acting at a cost to benefit others – benefits the altruist as well as the
beneficiary. The appeal of this ‘good news story’ is obvious: if it is true that ‘helping helps the
helper’, then encouraging people to be kind(er) to others could provide a simple, accessible,
inexpensive, self-sustaining and effective means of tackling a variety of social problems.
Here we outline existing theories of altruism and their relation to kindness, and consider
the predictions these theories make about well-being. And in order to investigate whether and to
what extent these predictions have been tested, and to give an overview of the literature as a
whole, we conduct a systematic review and meta-analysis of the experimental studies of the
effects of kind acts on the well-being of the actor. We end with a discussion of the limitations of
the existing literature, and make recommendations for future research.
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The causes of kindness
Humans are social animals. Their ancestors have been living in social groups for over 50
million years (Shultz, Opie, & Atkinson, 2011), and for the past 2 million years humans have
been making a living as intensely collaborative hunter-gathers (Tooby & DeVore, 1987). Social
life affords numerous opportunities for mutually beneficial cooperative interactions. And
humans, like other social animals, have been equipped by natural selection with a variety of traits
and dispositions – love, loyalty, benevolence and bravery – that enable them to seize these
opportunities. In addition, the human capacity for culture – the ability to invent and share new
ways of living – has allowed them to build and elaborate upon this benevolent biological
foundation, with rules, norms and other social institutions that further inculcate and amplify
cooperation and altruism (Hammerstein, 2003).
According to game theory – the mathematical analysis of social interaction – there is not
one type of cooperation, there are many, and hence many different types of social, cooperative
and altruistic behaviour (Curry, 2016; Lehmann & Keller, 2006; Nunn & Lewis, 2001; Sachs,
Mueller, Wilcox, & Bull, 2004). These theories make it possible to identify and distinguish
between several different ‘kinds of kindness’.
People will be kind to their families
Natural selection will favour altruism when the cost to the acting gene is outweighed by
the benefits to copies of that gene that reside in other individuals – that is in genetic relatives or
family members (Dawkins, 1979; Hamilton, 1964). As predicted by this theory of ‘kin selection’,
many organisms possess adaptations for detecting and delivering benefits (or avoiding harm) to
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kin (Gardner & West, 2014) — the most common example being parental care of offspring
(Clutton-Brock, 1991; Royle, Smiseth, & Kölliker, 2012). Humans have always lived in groups
composed mostly of genetic relatives (Chapais, 2014; Walker, 2014), and there is evidence to
suggest that they too possess adaptations for kin altruism. Humans detect kin by means of a
variety of cues, including maternal perinatal association, co-residence (Lieberman, Tooby, &
Cosmides, 2003, 2007), and possibly phenotype matching (DeBruine, 2005; Mateo, 2015). A
preference for helping kin has been demonstrated in numerous experiments (Curry, Roberts, &
Dunbar, 2013; Madsen et al., 2007). And human kin altruism is evident in patterns of parental
(Geary & Flinn, 2001) and grandparental (Euler & Weitzel, 1996) investment and its absence
(Daly & Wilson, 1996). It has also been argued that sympathy – a sensitivity to the needs of
others – originally evolved to facilitate parental care (Hublin, 2009; Preston & de Waal, 2002),
before becoming available to facilitate other types of cooperation.
Thus, kin selection can explain kindness in the form of love, care, sympathy and
compassion. And the theory predicts that these tendencies will be elicited by others who exhibit
cues of genetic relatedness, especially vulnerable children. Consistent with this perspective,
research has shown that men are more willing to donate money to children whose faces have
been digitally morphed to resemble their own (Platek, Burch, Panyavin, Wasserman, & Gallup Jr,
2002); and people are more generous when donating to charities using images of children with
negative (sad, distressed) as opposed to neutral emotional expressions (Burt & Strongman, 2005;
Small & Verrochi, 2009).
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People will be kind to members of their communities
Natural selection will favour altruism to those with whom the actor shares a common
interest – team mates, group members, coalition partners, and others who are ‘in the same boat’.
Game theorists typically model such ‘mutualistic’ interactions as coordination problems (D. K.
Lewis, 1969; Schelling, 1960) – including ‘stag hunts’ (Skyrms, 2004) and ‘soldiers
dilemmas’ (Clutton-Brock, 2009). The benefits of ‘working together’ are evident from the
ubiquity in nature of herds, shoals, flocks, and collaborative hunting (Boinski & Garber, 2000;
Boos, Kolbe, Kappeler, & Ellwart, 2011), as well as the formation of alliances and coalitions
(Bissonnette et al., 2015; Harcourt & de Waal, 1992). Coordinating to mutual advantage has been
a recurrent feature of the social lives of humans and their recent ancestors, especially with regard
to collaborative hunting (Alvard, 2001; Alvard & Nolin, 2002), and forming coalitions to
compete with rival coalitions (Wrangham, 1999). Humans have psychological adaptations for
detecting coalitions by means of a variety of different ‘badges of membership’ (Kurzban, Tooby,
& Cosmides, 2001; McElreath, Boyd, & Richerson, 2003; Pietraszewski, Curry, Petersen,
Cosmides, & Tooby, 2015; Tooby & Cosmides, 2010); and they spontaneously form, and are
altruistic to, their own groups (sometimes at the expense of other groups) (Balliet, Wu, & De
Dreu, 2014; Bernhard, Fischbacher, & Fehr, 2006; Sherif, Harvey, White, Hood, & Sherif,
1954/1961; Tajfel, 1970). Coordination to mutual advantage also seems to have spurred the
evolution of a sophisticated ‘theory of mind’ – the ability to think about what others are thinking
and feeling (Tomasello, Carpenter, Call, Behne, & Moll, 2005; Young, Camprodon, Hauser,
Pascual-Leone, & Saxe, 2010).
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Thus, mutualism (coordination to mutual advantage) can explain kindness in the form of
loyalty, solidarity, camaraderie, civic-mindedness, community spirit, and commitment to a cause
‘greater than oneself’. And the theory predicts that these tendencies will be elicited by other
members of the groups with which one identifies (including strangers) (Whitehouse & Lanman,
2014). Consistent with this perspective, research has demonstrated that geographical proximity
(and perhaps perceptions of cultural and genetic similarity) is a major predictor of the size of
U.S. donations to foreign communities affected by large scale natural disasters (Adams, 1986).
Research has also shown that participants primed with words related to ‘connectedness’ (for
example, ‘community’, ‘together’, ‘connected’, ‘relationship’) donated more money to charity
(Pavey, Greitemeyer, & Sparks, 2011).
People will be kind to their friends, and others whom they might meet again
Natural selection also favours altruism to those who might return the favour at a later date
(Axelrod, 1984; Trivers, 1971). Under some conditions – modelled by game theorists as
‘prisoner’s dilemmas’ – cooperation can be undermined by ‘cheats’, individuals who accept the
benefit of cooperation without paying the cost. In repeated interactions, a strategy of ‘conditional
cooperation’ or ‘reciprocal altruism’ – which initiates and continues cooperation with
cooperators, but which detects and avoids (or punishes) cheats – can overcome this ‘free-rider’
problem (Ostrom & Walker, 2002). Surprisingly, few if any examples of full blown ‘reciprocal
altruism’ have been found in non-human species (Amici et al., 2014; Clutton-Brock, 2009),
although some aspects of reciprocity have been identified in cleaner fish (Bshary & Grutter,
2006), vampire bats (Carter & Wilkinson, 2013), and primates (Mitani, 2009). However, it has
been argued that reciprocal social exchange has been a recurrent feature of the social lives of
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humans since our last common ancestors with chimpanzees 6 million years ago (Jaeggi &
Gurven, 2013); and there is some suggestive evidence for trade between human groups from
82,000 years ago (Bouzouggar et al., 2007). Humans appear to be equipped with adaptations for
detecting (Cosmides & Tooby, 2005), punishing (Price, Cosmides, & Tooby, 2002), and
forgiving (McCullough, Kurzban, & Tabak, 2013) ‘cheats’. And reciprocity emerges early in
children’s behaviour (Harbaugh, Krause, Liday, & Vesterlund, 2002), and is used cross-culturally
as a strategy for social exchange (Henrich et al., 2005; Kocher, Cherry, Kroll, Netzer, & Sutter,
2008).
Thus, reciprocal altruism can explain kindness in the form of trust (initiating
cooperation), returning favours, gratitude (for favours yet to be returned), forgiveness and
friendship. The theory can also explain kindness to strangers. An altruistic act may be the start of
a beautiful friendship, a way of making a new friend (after all, ‘a stranger is just a friend you
haven’t met yet’). And in any case, it might be better to ‘err on the side of caution’, and be
altruistic just in case you happen to see the person again (Delton, Krasnow, Cosmides, & Tooby,
2011; Krasnow, Delton, Tooby, & Cosmides, 2013).
The theory of reciprocal altruism predicts that these tendencies will most likely be
elicited in repeated interactions where individuals expect to meet again, where one’s cooperative
(or uncooperative) behaviour can be observed by others, and towards others who have helped
them in the past, or will be able to help them in the future (Kraft-Todd, Yoeli, Bhanot, & Rand,
2015). For example, in an experimental game investigating donations made in public to
UNICEF, researchers found that those who gave more money away received more from their
fellow players (Milinski, Semmann, & Krambeck, 2002). And in a test of eight different
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messages designed to increase organ donation, an appeal to ‘reciprocity’ – “If you needed an
organ transplant, would you have one? If so, please help others” – was found to be the most
effective (Harper, 2013; see also: Sanders, Halpern, & Service, 2013, Trial 4).
People will be kind to others when it enhances their status
Natural selection can also favour altruism if it intimidates rivals or impresses potential
mates. Organisms often come into conflict over resources such as food, territory, and mates
(Huntingford & Turner, 1987). Although such conflicts appear purely competitive, in fact there
are costs involved in conflict – time, energy, and injury – that individuals have a common
interest in avoiding. One way of avoiding a damaging fight is for contestants to display reliable
indicators of “fighting ability” (“resource holding power”, or “formidability”), and for the
weaker party to cede the resource to the stronger. In this way, the stronger party still wins, but
both avoid the costs of a real fight (Maynard Smith & Price, 1973). Such ‘ritual contests’ are
widespread in nature (C. W. Hardy & Briffa, 2013; Riechert, 1998). In stable social groups, in
which relative ‘power’ is already known by reputation (through direct experience or third-party
observation), individuals can dispense with the contest, and allocate disputed resources by
‘rank’. Such ‘dominance hierarchies’ represent a further de-escalation of conflict, and are also
widespread (Preuschoft & van Schaik, 2000). Depending on the species, displays of size, weight,
age, or experience may carry the day — but displays of altruism can also work (Gintis, Smith, &
Bowles, 2001; Zahavi & Zahavi, 1997). Humans and their recent ancestors have always faced
the problem of resolving conflict, because such problems are inherent in group living (Shultz &
Dunbar, 2007). And all human societies feature status hierarchies, which individuals (especially
males) seek to climb and derive satisfaction from climbing (Anderson, Hildreth, & Howland,
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2015; Anderson, Kraus, Galinsky, & Keltner, 2012; Mazur, 2005). As predicted, humans –
especially males – commonly engage in costly and conspicuous displays of prowess, resources,
and even altruism (including generosity and bravery), especially in the context of mate-
competition (C. L. Hardy & Van Vugt, 2006; Hawkes, 1991; Hawkes, O'Connell, & Blurton
Jones, 2001; Mazur, 2005; Miller, 2000; Smith & Bleige Bird, 2000). Experiments suggest that a
tendency for the strong to display status by helping the weak – noblesse oblige – is present cross-
culturally (Fiddick, Cummins, Janicki, Lee, & Erlich, 2013).
Thus, ‘competitive altruism’ can explain kindness in the form of generosity, bravery,
heroism, chivalry, magnanimity and public service. This includes acts of kindness to strangers.
Helping a stranger may improve your status (Barclay, 2011; N. J. Raihani & Bshary, 2015)
whether the recipient is in a position to return the favour or not. And the theory predicts that
these tendencies will be elicited in the presence of rivals, or potential mates, where acting
altruistically may enhance one’s status. Consistent with this perspective, research has shown that
male donors give more when donating to an attractive female fundraiser, especially in response
to a large donation made by a competing male (Nichola J. Raihani & Smith, 2015). (See also:
Bereczkei, Birkas, & Kerekes, 2007; Iredale & Van Vugt, 2011).
Summary
Thus multiple theories – kin altruism, mutualism, reciprocal altruism, competitive
altruism – explain multiple types of altruism, and multiple types of kindness. Although such
kindness is usually directed towards family, friends, colleagues and spouses, these theories also
explain kindness to strangers under some conditions. Rather than attempting to force these
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diverse theories and mechanisms into a single definition, for the remainder of this paper we will
simply use kindness, altruism, helping, prosociality and related terms interchangeably, to refer
broadly to actions that benefit others (at a cost to self), usually accompanied by benevolent
subjective emotions.
The consequences of kindness: Why would helping make you happy?
Broadly speaking, happiness (well-being, pleasure) can be seen as an internal reward
system for acting in ways that promote survival and reproduction (Buss, 2000). Happiness is: “a
psychological reward, an internal signaling device that tells us that an adaptive problem has
been, or is in the process of being, solved successfully” (Hill, DelPriore, & Major, 2013).
From this perspective, it is no problem to explain why ‘eating’ or ‘having sex’ makes
people happy. These behaviours meet important adaptive goals. And, for the reasons outlined
above, it is equally straightforward to explain why performing acts of kindness might make
people happy. It is because caring for family, maintaining coalitions, trading favours and
increasing status are also important adaptive goals. Indeed, we might even expect helping others
to produce more happiness than helping yourself. It is precisely because helping others can
sometimes give a better return on investment than helping yourself that evolution has favoured
kindness in the first place.
Thus, the evolutionary behavioural science approach to altruism predicts that people will
be happy to help family, friends, community members, spouses, and even strangers under some
conditions.
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This approach to kindness and well-being also predicts that there will be individual
differences in the degree to which individuals derive satisfaction for helping specific others. Like
all personality traits (Polderman et al., 2015), various different types of cooperative behaviours
have been found to be moderately heritable – including in-group favouritism (G. J. Lewis &
Bates, 2010), trust (Cesarini et al., 2008), and fairness (Wallace, Cesarini, Lichtenstein, &
Johannesson, 2007). And the satisfaction derived from helping others, and establishing
cooperative social relationships is no exception (Haworth et al., 2016). In addition, there are also
obvious situational and contextual factors that should make a difference. Just as a hungry person
derives more pleasure from eating than a full person, we should expect individuals with a greater
need or desire to establish cooperative relationships to derive more satisfaction from being kind
to others. For example, lonely or isolated people — perhaps those who have moved to a new city,
or a new school — might be happier to seize opportunities to make new friends, or connect with
their communities, than are people who ‘have enough friends already’ or who are well-
established in their communities. Ambitious people (with more resources to spare) seeking status
may have a greater appetite for, and be happier to seek, opportunities for conspicuous altruism or
public service — “You make a living by what you get; you make a life by what you give”
according to the quote often attributed to Winston Churchill. Single people who are courting
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may be happier to help potential mates. Indeed, we might also expect sex differences, with
women happier to help children, and men happier to perform chivalry or heroics.
To what extent have these predictions been tested, and received support, from the existing
literature on well-being? In order to find out, below we conduct a systematic review and meta-
analysis of the experimental literature on the effects of kind acts on the well-being of the actor.
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And again, given that well-being encapsulates a range of states and associated
behaviours (OECD, 2013), and is generally "measured by simply asking people about their
happiness” (Dolan & Metcalfe, 2012), for the remainder of this paper we will use well-being,
happiness, life-satisfaction and related terms interchangeably.
The present study
The past decade has seen a growing interest in the relationship between kindness and
well-being. A large number of research groups and charity organisations have been created to
pursue and promote the idea that, for example, ‘random acts of kindness’ boosts the well-being,
happiness and mental health not only of the recipient, but also the actor (see S1). The idea has
even been explored by the UK government (Aked, Marks, Cordon, & Thompson, 2008; Aked &
Thompson, 2011; Huppert, 2009; Laura Stoll, 2011). The appeal of the idea is clear: it suggests
that there is a simple, effective, inexpensive and widely-available means of addressing social
problems ranging from social isolation to more serious mental and physical health conditions.
What is the evidence for the claim that altruism makes the altruist happy? A large body of
research has established an association between kindness and happiness and health (Anik, Aknin,
Norton, & Dunn, 2009; Konrath & Brown, 2013). However, much of the research has been
correlational — showing, for example, that around the world people who spend more money on
others are happier (Lara B. Aknin et al., 2013), or people who volunteer to help others are
healthier (Jenkinson et al., 2013).
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While such correlational evidence is consistent with the prediction that people will be
happy to help others, it is not sufficient to establish a causal relationship between kindness and
happiness. After all, it’s possible that helping makes you happy, but it could also be that
happiness makes you helpful, or it could be that some third variable – health, income, personality
– makes you both happy and helpful.
The distinction between correlation and cause is not a mere philosophical nicety; it is a
genuine difference with important practical implications. In the absence of a clear causal
connection, kindness interventions may not work. They may waste time and money, or displace
other more effective interventions. Worse, they may be counter-productive. If happiness causes
helping (rather than the other way around), then forcing unhappy people to help may make them
less happy still.
In order to establish that performing acts of kindness can cause happiness, what’s needed
is experimental research that randomly allocates participants to kindness and non-kindness
conditions, and then measures and compares their subsequent happiness. And so we undertook a
systematic review and meta-analysis of this experimental literature. The review sought to answer
two questions. First, to what extent have the theories of the effects of kindness on well-being
outlined above been tested and supported? Second, what is the overall effectiveness of kindness
interventions on well-being?
Methods
In order to identify suitable experimental studies of the effects of altruism on the altruist's
well-being, we conducted searches of the scientific databases Web of Science and PsychInfo for
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academic articles. The most recent search was conducted on 1st September 2016. The process is
summarised in the flow diagram in Figure 1. We used the search string: (kindness OR altruis*
OR prosocial OR co-operat* OR cooperat*) AND (wellbeing OR well-being OR happiness)
AND (experiment* OR control OR condition OR random* OR empirical OR trial) NOT
mindfulness OR meditation OR loving-kindness. This search identified 639 articles. To this we
added 19 articles identified by other means (following references in books and journal articles,
Google scholar searches, viewing academic researchers’ web-pages). After removing duplicates,
we were left with 428 articles.
This initial set of 428 articles was screened. Two researchers (LAR and OSC) read the
titles and abstracts. Subsequently 380 articles were excluded for not meeting the inclusion
criteria. These articles were not experimental (that is, they were qualitative or correlational); or
the kindness-well-being effect was reversed (that is, they looked at whether making people
happy made them kinder, or whether kindness made the recipient happy or healthy); or they were
review papers presenting no new data; or they were on topics not directly relevant to the current
review and in which the effect of kindness on well-being was not measured (for example, drug-
alcohol rehabilitation programmes; kindness in animal husbandry; climate change and planetary
wellbeing; loving-kindness meditation/mindfulness). Cases in which the researchers disagreed
were given greater scrutiny and discussed, and where no consensus was reached, the articles
were included in the next stage of the analysis.
The remaining 48 articles were then read in full, and assessed for appropriateness for the
meta-analysis (see S2 for the full list). This process excluded a further 29 records (and several
studies from included articles) for reasons summarised in Table S1. At the end of this process
3
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we were left with 19 articles, containing a total of 21 studies that had experimentally tested the
hypothesis that kindness causes well-being.
For each of these 21 studies we coded the following characteristics:
(a) theory of kindness being tested
(b) mean age of sample
(c) sex of participants
(d) location of study
(e) type of altruist (for example, whether sample was likely to be especially in need
of social connection)
(f) type of recipient (for example, whether family, friend, stranger)
(g) the nature of the intervention (for example, ‘random act of kindness’, prosocial
purchase, charitable donation)
(h) size of the intervention group
(i) nature of the control (for example, no treatment, self-kindness, other activity)
(j) size of the control group
(k) dependent measure (for example, well-being, happiness, life-satisfaction)
(l) effect size (Cohen’s d)
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When coding studies with multiple (control) groups, and / or multiple dependent
measures, we chose the most appropriate comparison (usually kindness versus neutral) and the
most appropriate measure (usually some measure of happiness).
Results
Study characteristics
The characteristics of the 21 studies are presented in Table 1. These 21 studies included a
total of 2,685 participants (~34% male, mean age ~25.49, SD=12.39). The majority of
4
participants came from Canada, USA and Europe, although there were also studies conducted in
South Africa, Korea and Vanuatu. Most participants were university students, although there
were also two studies with children, one study of Vanuatu villagers, and one with elderly
participants.
The two most common interventions were ‘acts of kindness’ and ‘prosocial purchasing’.
Typical instructions for the ‘acts of kindness’ intervention were as follows:
“During the coming week, please perform at least five acts of kindness per day
and report on them in the evening, including the responses of others that you
received. Examples of acts of kindness are: holding a door for someone at
university, greeting strangers in the hallway, helping other students in preparing
for an exam, etcetera. It does not matter whether you address your acts of
kindness to people you know or not” (Ouweneel, Le Blanc, & Schaufeli, 2014).
Prosocial purchasing interventions involved giving participants a sum of money, and
instructing them to spend it on someone else.
Most studies used a self-report measure of subjective well-being, happiness, life-
satisfaction, or positive and negative affect. These included the Subjective Happiness Scale
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(SHS; S. Lyubomirsky & Lepper, 1999), the Steen Happiness Index (SHI; Seligman, Steen, Park,
& Peterson, 2005), the Satisfaction With Life Scale (SWLS; Diener, Emmons, Larsen, & Griffin,
1985), and the Positive Affect and Negative Affect Scale (PANAS; Watson, Clark, & Tellegen,
1988). Three studies used more objective measures: two used other-rated smiling, and one used
blood pressure.
Scrutiny of the 21 studies identified a number of methodological limitations.
Crucially, from the point of view of the present study, we found that almost all of the
studies were designed to investigate the effects of kindness in general; none of the studies
distinguished between the different types of kindness outlined above. Hence none of the studies
systematically varied the type of altruist (for example, those in need of friends, and those not in
need; the majority of participants were ‘typical’ although two studies focussed on ‘socially
anxious’ individuals). And none of the studies systematically varied type of recipient, for
example family, colleague, friend, stranger; in most cases the recipient was left unspecified – that
is, they could be ‘anyone’. This means that the predictions regarding the effects of kindness on
the well-being of different types of altruists, with regard to different types of recipients, has not
been tested by previous research, and could not be tested by the present meta-analysis.
We also identified a number of other potential problems.
In two studies, participants were not only not blind to the hypothesis, but were explicitly
told that performing acts of kindness would improve their mood (Nelson et al., 2015; Trew &
Alden, 2015).
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There was also considerable variation in control conditions. Some studies compared
acting kindly with doing nothing (thus possibly confounding the effects of kindness with the
effects of performing any novel fun activity), whereas others compared acting kindly with some
other similarly interesting activity. (For a direct comparison of these two control conditions, see:
Buchanan & Bardi, 2010).
There was also considerable variation in whether the kindness intervention involved a
cost to the actor. Most ‘acts of kindness’ involved a cost; but, the ‘prosocial spending’ studies
that involved a windfall payment to the participant did not. It was not even clear that spending
the windfall on others even constituted an opportunity cost. In two studies, the intervention
involved either keeping or donating a children’s goody bag (consisting of chocolate and juice)
(Lara B. Aknin et al., 2013; L. B. Aknin, Fleerackers, & Hamlin, 2014). For the adult participants
in the study, keeping a child’s goody bag is not presumably not much of a benefit, and donating it
not much of a cost.
We also note that many studies exhibited many ‘researcher degrees of
freedom’ (Simmons, Nelson, & Simonsohn, 2011), through the use of multiple dependent
measures; and that the results across these measures were not always consistent (for example, the
intervention would improve ‘positive affect’ but not ‘life satisfaction’, or vice versa). Similarly,
studies varied in duration, and were able to report results from multiple different times, not all of
which were consistent. For example “The kindness intervention had a positive influence on both
positive emotions and academic engagement, though not in the long run” (Ouweneel et al.,
2014).
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However, in the interests of providing as broad an overview of the experimental literature
as possible we erred on the side of including these studies in the meta-analysis.
Meta-analysis
Meta-analysis was conducted in SPSS V21 and R, following the recommendations
summarised in (Field & Gillett, 2010).
A random-effects model revealed that the mean effect size of the 21 studies was d = .38,
95% confidence interval (CI) = [.27, .49], Z = 6.92, p < .001 (see Figure 2). This is a small-to-
medium effect, approximately equivalent to an increase of 0.8 on a standard 0-10 happiness scale
(Helliwell, Layard, & Sachs, 2016).
A chi-square test of homogeneity of effect sizes was not significant, 2(19) 21.35, p=.38.
These measures suggest considerable similarity in effect sizes across studies.
Moderator analysis suggested that the effect of age or sex on the overall effect size was
not significant. However, as noted above, limitations in the design of the studies meant that
further moderator analysis — for example, to investigate the effects on the well-being of
different types of altruists of giving to different types of recipients — was not possible.
A file-drawer analysis, revealed that 653 unpublished, filed, or unretrieved studies would
be required to bring the significance of this average effect size to nonsignificance.
However, there was evidence of significant publication or reporting bias. Visual
inspection of the Funnel plots (Figure 3) suggests – and Begg's test τ(N = 21) = 0.31, p = 0.046
confirms – that smaller studies tended to find larger effects. This indicates that smaller studies
finding smaller (or negative) effects have not been submitted or published. Adjusting for severe
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to moderate one-tailed selection suggests that the true effect size is likely to be 0.31 d 0.35
(Vevea & Woods, 2005).
Discussion
The results of this systematic review and meta-analysis of the experimental kindness
literature suggests that the overall effect of kindness interventions on happiness is small-to-
medium (d 0.38). These effects are comparable to other positive psychology interventions
(d=0.34, Bolier et al., 2013; d=0.31, Sin & Lyubomirsky, 2009; d=0.44, Weiss, Westerhof, &
Bohlmeijer, 2016). This suggests that performing acts of kindness will not change your life, but
5
might help to nudge it in the right direction.
However, perhaps a more important discovery of the present review is that the
predictions of the various theories of kindness outlined above – kin altruism, mutualism,
reciprocal altruism, competitive altruism – have not been tested by previous empirical work. The
studies reviewed here have instead focussed on kindness ‘in general’, rather than any of the more
specific theories. This huge gap in the literature means that there are many very basic questions
about the relationship between kindness and well-being that remain unanswered. For example,
we do not know whether people are happier giving to family and friends, as opposed to
(anonymous) strangers. (In fact, because no study investigated the effects of acting at a cost to
help an (anonymous) stranger, there is no evidence (either way) on whether helping strangers
makes you happy.) We do not know whether people are happier giving to needy or unlucky
recipients, as opposed to affluent or lazy recipients. We do not know whether people are happier
giving to children as opposed to adults; in-group as opposed to out-groups; females as opposed
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to males. Nor do we know whether some people benefit from performing acts of kindness more
than others. We do not know whether lonely people appreciate the opportunity to reach out to
others more than people whose ‘diaries are full’. We do not know whether single people are
happier performing romantic gestures than couples. We do not know whether men and women
are happier performing different types of kindness acts. Nor do we know how these two variables
interact – that is, whether the effect of specific types of helping depend on the specific type of
helper.
It is imperative that future research fill these gaps – uniting theory, experiment and
practice. After all, the overall effect size reported above is the average across all types of altruists
and recipients (including those for whom it works, and those for whom it does not). With the
help of more precise theories regarding which altruists, and which recipients, benefit most, future
research should be able to identify the kind of kindness that works best, and enable practitioners
to ‘put their good where it will do the most’.
To that end, in order to overcome the limitations of previous research, we make the
following recommendations for future research:
There is no scientific theory that predicts that humans will be selfish under all conditions.
Thus, repeatedly testing the folk intuition that people are selfish, and finding that they are not,
makes no contribution to science. Future research on the effects of kindness on well-being should
instead focus on developing and testing the more fine-grained predictions of the numerous
theories of altruism outlined above. Specifically, future research should investigate whether
people are happier to help some types of people more than others — for example, family and
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friends as opposed to anonymous strangers. We note that, in the present review, some of the
studies with the largest effect sizes involved altruism towards ‘friends and family’ (L. B. Aknin,
Broesch, Hamlin, & Van de Vondervoort, 2015; L. B. Aknin, Dunn, Whillans, Grant, & Norton,
2013; Geenen, Hoheluchter, Langholf, & Walther, 2014); and other studies have shown that
‘social connection’ with the recipient increases positive affect in the donor (L. Aknin, Dunn,
Sandstrom, & Norton, 2013; L. B. Aknin, Sandstrom, Dunn, & Norton, 2011). But the findings
of these studies need to be replicated more systematically. There is already a large literature on
whether people behave more or less altruistically to specific types of people; it would be fairly
straightforward to add measures of subjective well-being to replications and extensions of these
designs.
Future research should also investigate whether performing acts of kindness benefits
some types of people more than others. Do people with a greater desire for social connections
benefit from being benevolent more than others? To what extent does sex, age and income
influence the satisfaction derived from acts of kindness? Do personality traits, and social and
moral values, play a mediating role? Do kindness interventions have a greater effect on some
mental health problems than others, perhaps those most related to social interaction? And are
kindness interventions particularly effective with people (re)integrating into society after being
absent from it – recent immigrants, ex-offenders, recovering addicts?
Future research could also seek to generalise these findings by employing more
representative community samples (including participants diagnosed with specific mental health
problems) and fewer college students, as well as conducting further cross-cultural experiments
(Henrich, Heine, & Norenzayan, 2010). Such research could harness the unparalleled data
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collection opportunities provided by the internet, including on-line fundraising platforms. And,
given the predicted importance of non-anonymous, face-to-face contact for cooperation and
social relations, these internet methods should be combined with field experiments to further
generalise the finding, establish external validity, and pilot actual interventions.
In addition, given that our meta-analysis suggests that the population effect may be as
low as d = 0.31, in order to detect such an effect with power β = 0.80, future researchers should
use a sample size of at least 272 per group (Faul, Erdfelder, Lang, & Buchner, 2007). We note
that none of the studies reviewed in this meta-analysis met this criteria (average sample size =
64; average β = 0.41), and that such low-powered studies are likely to fail to detect an effect even
if it is there.
Future research could also investigate the effects of different types of altruism on the
recipient which, despite a couple of interesting studies, has yet to be systematically studied
(Baskerville et al., 2000; Pressman, Kraft, & Cross, 2015). For example, are people happier to be
helped by family, and friends as opposed to strangers? By in-group members as opposed to out-
group? Is there any element of shame or resentment at being a ‘charity case’? Was Orwell right
to argue that “A man receiving charity always hates his benefactor”. To what extent are people
suspicious of the motives of altruistic strangers?
Looking further ahead, future research should also consider the long-term consequences
of acts of kindness. Research on the ‘hedonic treadmill’ suggests that people might have a
hedonic ‘set point’ that they return to whatever happens to them, good or bad (Ryan & Deci,
2001). So it’s possible that existing outcome measures, which tend to rely on self-report well-
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being, are looking for effects in the wrong places (or at the wrong times). Happiness is a quick
hit, which rewards you now for doing things that have long-term benefits in the future. So, rather
than chasing the fleeting effects of happiness, it might be better to employ or develop measures
that assess those long-term benefits. If the function of altruistic behaviour is to help families,
improve communities, make new friends, find a mate, or increase status, then studies should be
measuring these outcomes. Do people allocated to the kindness condition report better relations
with their families? More identification with their communities? More friends? More sexual
partners (Arnocky, Piché, Albert, Ouellette, & Barclay, 2016)? More committed relationships
(Kogan et al., 2010)? More resilient marriages? More recognition and honours? More pride in
one’s achievements (Sznycer et al., submitted)? If so, then future research might be able to
finally connect the two types of happiness — hedonic and eudaemonic — that have hitherto
remained apart.
Conclusion
Through sheer chance and serendipity random acts of kindness may have desirable
consequences, perhaps in ways that could not have happened otherwise. But by their very nature,
random acts are unlikely to be directed towards those who need them, or might appreciate them,
the most. And we have shown that their effects are relatively modest. Could better outcomes be
achieved for the same amount of effort? Might non-random acts of kindness to significant others
have greater effects than random acts of kindness to strangers? Further empirical work is
required to answer these important questions. This research will advance our understanding of
the causes and consequences of kindness, and help practitioners to maximise the effectiveness of
kindness interventions – helping people to reconnect with their families, get to know their
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neighbours, make new friends, meet a mate, play an active role in their communities, and
compete in socially productive ways.
"27
HAPPY TO HELP
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Endnotes
Although this quote may be falsely attributed (http://www.winstonchurchill.org/resources/quotations/135-quotes-
1
falsely-attributed).
Even then the effects are modest. This meta-analysis of the relationship between volunteering and health in the
2
elderly found that volunteers were 22% less likely that non-volunteers to die during the follow-up period of the
studies (Jenkinson et al., 2013). However, the import of this finding depends on the base-rate. By way of illustration,
if on average 10 out of 1000 (1%) non-volunteers die during the follow-up period, then a 22% percent decrease
means that 7.8 out of 1000 (0.78%) volunteers would die during the same period. Moreover, as this review goes on
to say: “These findings were not confirmed by experimental studies.”
The most highly cited paper in the kindness literature (with 597 citations at the time of the last search) purports to
3
provide evidence that kind acts boosts the well-being of the actor (Sonja Lyubomirsky, Sheldon, & Schkade, 2005).
However, the article does not report the size of the sample, the dependent measure, or any inferential statistics (for
example, effect size or significance). Email correspondence with the author revealed that the data are no longer
available.
These averages are approximate (~), because the age and sex ratio of the samples were not available for some
4
studies.
Although see Coyne (2014a, 2014b) for critical commentary on (Sin & Lyubomirsky, 2009) and (Bolier et al.,
5
2013).
"48
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