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RESEARCH ARTICLE
Qualitative analysis of the Best Possible Self
intervention: Underlying mechanisms that
influence its efficacy
Alba CarrilloID
1
, Marian Martı
´nez-Sanchis
1
, Ernestina Etchemendy
2
, Rosa M. Baños
1,3
*
1Department of Personality, Assessment and Psychological Treatments, University of Valencia, Valencia,
Spain, 2Department of Psychology and Sociology, University of Zaragoza, Teruel, Spain, 3CIBER
Fisiopatologı
´a Obesidad y Nutricio
´n (CIBEROBN), Instituto Carlos III, Madrid, Spain
*banos@uv.es
Abstract
Background
The Best Possible Self is a Positive Psychology Intervention which asks participants to write
down about themselves in their best possible future. Previous studies have shown its effi-
cacy to enhance wellbeing, but the mechanisms that underlie its efficacy are still unknown.
Objective
The aim of this study was to analyze the content of the essays of the BPS intervention and
to examine how this content was related to the efficacy of the intervention to increase posi-
tive affect.
Method
Participants (N = 78) were randomized to either the Best Possible Self condition, or one of
two variants of the intervention: one’s best self in the present, and one’s best self in the past.
Qualitative analyses of the texts were carried out to explore the main themes and features
of the essays. Then, a mixed-methods approach with quantitative and qualitative data was
followed, in order to analyze the relationship between the content of the texts and the
change in positive affect produced by the interventions.
Results
Significant differences between conditions were found in the content of the compositions.
Regression analyses showed that different variables predicted the change in positive affect
depending on the condition. Mediation analyses also found differences among conditions.
Conclusions
These findings suggest that these interventions respond to different underlying mechanisms
which influence their efficacy. This study contributed to a better understanding of how Posi-
tive Psychology Interventions work, and how to increment their efficacy.
PLOS ONE | https://doi.org/10.1371/journal.pone.0216896 May 17, 2019 1 / 15
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OPEN ACCESS
Citation: Carrillo A, Martı
´nez-Sanchis M,
Etchemendy E, Baños RM (2019) Qualitative
analysis of the Best Possible Self intervention:
Underlying mechanisms that influence its efficacy.
PLoS ONE 14(5): e0216896. https://doi.org/
10.1371/journal.pone.0216896
Editor: Simone Rodda, University of Auckland,
NEW ZEALAND
Received: January 18, 2019
Accepted: April 29, 2019
Published: May 17, 2019
Copyright: ©2019 Carrillo et al. This is an open
access article distributed under the terms of the
Creative Commons Attribution License, which
permits unrestricted use, distribution, and
reproduction in any medium, provided the original
author and source are credited.
Data Availability Statement: Data files are
available at https://doi.org/10.5281/zenodo.
2662545.
Funding: This work was supported by the
Conselleria d’Educacio
´, Investigacio
´, Cultura i
Esport (Spain) under the grant “INTERSABIAS”
(PROMETEO/2018/110). The funders had no role
in study design, data collection and analysis,
decision to publish, or preparation of the
manuscript.
Introduction
Historically, individuals have made profuse efforts to achieve the road of happiness and wellbe-
ing. Lately, these efforts have crystallized in the Positive Psychology research movement,
whose aim is to provide an evidence-based framework for the study of what makes people
happy and how to bolster their wellbeing levels [1]. Although there is a lack of a unified defini-
tion of wellbeing, one of the main historical approaches proposes wellbeing as the balance
between positive and negative emotions and a high sense of satisfaction with life, also known
as subjective wellbeing (SWB) [2]. Positive Psychology Interventions (PPIs) emerged precisely
as a response to the societal need of increasing people’s overall wellbeing levels, including
SWB. This applied portion of Positive Psychology consists of activities aimed at increasing pos-
itive emotions, cognitions or behaviors [3,4]. Research on the efficacy of these interventions
has burgeoned since its beginning, and nowadays there are multiple published studies about
new and heterogeneous exercises that can help people flourish (e.g. gratitude letters, acts of
kindness, using signature strengths). Indeed, several meta-analyses have shown that PPIs are
effective approaches to increase wellbeing with small to moderate effect sizes [4,5].
Lately, as a consequence of the progression in the knowledge of these interventions,
research interest on the mechanisms that explain the efficacy of PPIs is growing. To date, some
authors have attempted to explain why and under which circumstances PPIs work, developing
some theoretical models that can be applied to all PPIs in general (e.g. [6,7]). However, this
field is considerably recent, and these models still need to be validated [8]. In addition, they
are applied to the complete range of PPIs despite their heterogeneity, hence there is a lack of
knowledge about the circumstances that make each intervention individually effective [5,6].
One of the most widely used PPIs is the Best Possible Self (BPS) intervention, in which par-
ticipants are asked to write down about their best possible self in a future where they have
achieved everything desired, after working hard towards it. This intervention was developed
initially by King [9], and it was based on the trauma writing paradigm, which had found that
writing sessions about upsetting and negative topics (as a traumatic event) produced both
physical and mental health improvements [10,11]. As a response to the emerging interest in
the positive side of life [1], the focus of attention in research changed from the trauma writing
paradigm to the positive writing paradigm (i.e., writing about positive topics) and its effects on
wellbeing, being the BPS intervention one of its main examples. Based on the writing paradigm
of Pennebaker, King [9] developed this intervention and compared it with a writing disclosive
exercise about a traumatic event. Results showed that BPS intervention produced the same
benefits as trauma-focused writing on health. This intervention, in addition, produced signifi-
cant increases in positive mood and wellbeing, and participants in this condition rated the
exercise as less upsetting than the trauma condition participants. These results are consistent
with the last meta-analysis about disclosive writing, which found no significant differences
between interventions focused on disclosing negative events and the ones focused on disclos-
ing positive events on psychological and health benefits [10]. As the author of this work stated,
given that trauma writing paradigms usually produce temporary increases in negative affect,
choosing the disclosure of positive events may be preferable, as it avoids this short-term nega-
tive side effects and it has shown the same positive results.
Since the first approach by King, many studies have been carried out in order to test the
efficacy of this PPI. A narrative review of this intervention concluded that it seems a viable
approach to produce positive outcomes on wellbeing, although little is known about how this
positive activity works [12]. In addition, a recent meta-analysis about 28 studies showed that
BPS is an efficacious intervention to improve wellbeing and found moderate effect sizes of BPS
over control groups on positive affect (d = .339 and d = .657) [13]. However, analyses of
Qualitative analysis of the Best Possible Self
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Competing interests: The authors have declared
that no competing interests exist.
moderators (i.e., length, dosage, delivery method, etcetera) did not show significant results in
this review. Therefore, the characteristics of the BPS intervention that might influence its effi-
cacy are still unknown.
A methodological approach that has potential to unveil the possible mechanisms that
underlie the efficacy of a writing intervention is a qualitative analysis of its content. This
approach has the ability to uncover novel and deeper understandings of phenomena of interest
in Positive Psychology [14]. In addition, when combined with quantitative data in a mixed-
methods approach, qualitative data can help to identify significant predictors of wellbeing,
producing a more comprehensive outlook of relevant constructs and addressing questions as
why and how [15].
Recently, the benefits of positive writing have derived to an increasing interest on the quali-
tative variables of the writing tasks, although research is still scarce. In the case of the BPS
intervention, only a handful of studies explored the content that participants wrote about.
King [9] found that the BPS essays included a variety of topics, such as job success, self-
improvement, marriage and family, travel, or home ownership, although no further analyses
were carried out on the frequency of these topics. Hill and colleagues [16] analyzed the texts of
the BPS compositions in order to classify the goals included in the essays and found fourteen
categories. The most frequent goals were approach (those with references to approaching
something positive), intrapersonal (goals that mentioned only the self), and achievement (those
goals related to accomplishing a goal or achieving success). Correlation analyses were carried
out to explore the association between written goals and measures of life satisfaction and religi-
osity. Results showed that life satisfaction was negatively correlated with spirituality goals
(related to a higher power and/or to unity and justice). In addition, Loveday et al. [17] carried
out a thematic analysis of the BPS texts specifically focused on spare time using an explicit con-
ceptual framework on leisure [18]. Results showed that within the leisure area, affiliation (lei-
sure spent with other people), autonomy (leisure spent on oneself) and detachment-recovery
(leisure mentioned in relation to work) were the most frequent themes (33, 23, and 21 percent-
age of leisure sentences, respectively). However, this study only addressed the content of the
essays within the previously mentioned framework–focused on spare time, and only analyzed
the sentences coded as leisure, which represented 41% of the content, whereas the remaining
59% of the sentences categorized as non-leisure were not explored. As it can be seen, these first
approaches have explored the qualitative characteristics of the texts of the BPS essays, but they
were carried out within specific frames that might have constrained their results. Hence, there
is still a scarce knowledge about which content, in general, participants include in their essays
when they write about their BPS, and a broader approach could contribute to a better under-
standing about this subject. In addition, none of these studies have combined the content anal-
yses with quantitative data about the efficacy of the intervention, thus the role that the content
of the texts may play on its efficacy is still unknown.
This study is part of a larger project on the mechanisms that underlie the efficacy of the BPS
intervention [13], in which the role of temporality was explored. A randomized controlled trial
with three experimental conditions (the original BPS and two temporal variations: past best
self or BPAS and present best self or BPRES) showed that temporal focus did not affect the
ability of the intervention to increase positive affect as no statistically significant differences
emerged among conditions. Therefore, it is necessary to continue investigating on the under-
lying mechanisms that influence the efficacy of the BPS.
The main objective of the present work was to analyze the role of the content of the essays
of the BPS intervention on its efficacy. For this purpose, qualitative analyses of the BPS and the
BPRES and BPAS variants were carried out. More specifically, this work had two aims. On the
one hand, to analyze the content of the texts in order to identify the main themes and features
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of the compositions of the three PPIs (BPAS, BPRES, BPS) and to explore the possible differ-
ences between conditions. On the other hand, to examine the influence that the identified
themes and features of the texts had on the efficacy of the interventions to increase positive
affect. As far as we know, this is the first study that systematically analyzes the content of the
texts of the BPS with a bottom-up approach (not forced by a predetermined model), and the
first one that includes the temporal variants of this intervention. In addition, this is the first
work that combines qualitative data of the interventions with quantitative data about their effi-
cacy. It was expected that the content of the texts would influence on the efficacy of the three
PPIs to increase positive affect. However, due to the exploratory nature of the analyses, no spe-
cific hypotheses were generated regarding the content of the texts on each intervention and
how it may affect the efficacy of the intervention.
Method
Participants
The initial sample consisted of 84 participants who were part of a larger study [13]. Their age
ranged from 18 to 40 years old (M = 20.23, SD = 4.10), and 77.2% of them were women. They
were randomized to one of three conditions: BPAS (N = 30), BPRES (N = 27), BPS (N = 27).
Two participants did not answer post-intervention assessment, and text analyses showed that
four participants did not follow the instructions of the assigned conditions. Consequently, six
participants were excluded from the study. The final sample consisted of 78 participants
(BPAS = 27, BPRES = 25, BPS = 26).
Interventions and procedure
This study included three PPIs, based on the original BPS exercise. The BPS intervention asks
participants to visualize themselves in the future after everything has gone as well as possible
[19,20]. Based on this intervention, two variants of the exercise were designed with the same
format and instructions, except for the time frame in which they were focused on. Concretely,
the Best Past Self condition (BPAS) required to recall a time in the past when participants con-
sidered they had displayed the best version of themselves, whereas the Best Present Self condi-
tion (BPRES) asked participants to think about the best version they offered to the world at the
present time.
The procedure was based in previous studies: participants were encouraged to write about
their best self and then to mentally visualize this content [19,21,22]. The complete intervention
lasted 7 days, in which participants came to the laboratory for the first session and then prac-
ticed the assigned exercise at home for one week. During the first session, participants signed
the informed consent, answered the pre-intervention assessment and listened to audiotaped
instructions of the assigned task. Regardless of the condition, they had to spend 15 minutes
writing their essay in a computer in the laboratory, and then 5 minutes visualizing its content
(their best self) [19,23]. Instructions in all conditions encouraged participants to include as
many sensorial details as possible, as the procedure included an explicit visualization compo-
nent in which they spent 5 minutes visualizing about their best self after writing about it
[19,23]. During the remaining 6 days, participants were encouraged to mentally visualize the
content of their essay once a day. After 7 days, participants received a link with the post-inter-
vention assessment.
This work was registered in the United States National Institute of Health Registration Sys-
tem (http://www.clinicaltrials.gov) with Clinical Trials Registration Number NCT03024853
and approved by the ethical committee of the University of Valencia (H1415802387094).
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Scales
A mixed-methods approach using quantitative and qualitative methodologies was followed in
order to explore the relationship between the content and features of the texts and the change
in positive affect.
The quantitative outcome measure included was positive affect, as it has been widely used
in previous studies (e.g. [19,20,24]). The scale used to measure positive affect (PA) was the PA
subscale of the Positive and Negative Affect Scale, PANAS [25], which includes 10 positive
emotions (e.g., inspired) to measure positive mood. Respondents rate how they usually feel on
a 5-point Likert-type scale. In this study, a Spanish version was used [26].
Cronbach’s alpha for the original scale ranged from .86 to .90, and in this sample alpha
value was .90. Participants answered the scale the first day before practicing the assigned exer-
cise (pre-intervention assessment), and 7 days after the intervention started (post-intervention
assessment).
Coding of the essays
Essays were analyzed to explore two main areas. On the one hand, the content of the essays
(i.e., what did participants write about when they reflected on their best past, present or future
self). On the other hand, the features of the compositions or, in other words, how they
expressed these ideas (e.g., the number of words or its emotional valence).
The followed approach was based on the consensual qualitative research-modified
(CQR-M), a qualitative research method designed to be applied in large samples (i.e., more
than 15 participants) and relatively brief qualitative data, which can be used to describe little-
studied phenomena and establish a basis for further research. This method is defined as a bot-
tom-up approach, through which categories are derived from the data instead of forcing a pre-
determined structure on it [27]. With this method, as the authors state, a further
comprehension of the topic under research can be obtained by combining the newly described
phenomena with quantitative data.
In order to reach consensus, following the CQR-M guidelines, all team members discussed
disagreements at each step of the process. The coding team was composed by the first and sec-
ond authors (AC and MMS), who were experts on the interventions used in the study, knew
the instructions and procedure and had previously conducted studies with the included activi-
ties. The next procedure was followed: first, two independent coders (AC and MMS) read all
the essays independently and generated a list of themes and areas identified in the texts. Sec-
ondly, these themes were discussed by the researchers, and then the revised themes were
applied in the analyses of 30 randomized essays, in order to explore whether these were ade-
quate and captured all the relevant ideas. After a revision of the themes, all essays were ana-
lyzed independently by the two coders in order to categorize all the contained bins of
information with the designated themes and the subsequent areas. Interrater reliability and
frequency of themes were calculated (see Method and Results sections).
These themes were not mutually exclusive. In addition, since this analysis relied on bins of
information, they did not necessarily coincide with a complete sentence: it was possible that a
single sentence contained two ideas (for example, “the social area is very important in my life:
I like to communicate with people and I tend to be quite open and affectionate”, would be
coded as friendship and positive features), and it was also possible that the same idea expressed
in two or more sentences would be coded as one unit (for example, the two sentences “I want
to expose myself to what life brings to me. I want to feel inexperienced to able to improve”
would be categorized as positive features).
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Themes of the texts. The final categories included could be grouped into four areas: per-
sonal, academic/professional, social, and leisure area. Regarding personal area, positive features
collected all phrases that expressed a personal improvement on one’s trait or psychological
ability, or an already present positive feature that remained constant (e.g., “In the future I
would like to have the same psychological abilities that I currently have”); skills referred to the
presence or the willingness to learn an ability or knowledge (e.g., “I would like to learn how to
play the piano or the harp”); and health was coded when participants talked about their
attempts to influence their physical health (e.g., “My best self figured out my intestinal problem
and now she’s thin and strong”). Concerning the academic or professional area, themes were
divided by the inner motives expressed in the texts, being intrinsic the content related with the
academic or professional area associated with intrinsic motives (e.g., “Now I have a job in
which I feel very happy, and I have realized that I love my job”), and extrinsic when extrinsic
motives were expressed (e.g., “I visualize myself wearing a suit and having quite a lot of
money”). With respect to the social area, friendship was coded on phrases containing social
relationships with friends or colleagues (e.g., “I felt very close to my childhood friends because
we were all going through the same phase”), family on mentions to relationships with mem-
bers of the family (e.g., “When I get home, I tell my family about my day and I hear about
theirs”), partner in the case of romantic relationships (e.g., “I had a partner with whom I
enjoyed our shared moments”), and help emerged when participants made an explicit reflec-
tion on their willingness to or their actions aimed at helping other people in different contexts
(e.g., “I decided I would watch over the happiness of others, trying to improve their lives”).
Lastly, the leisure area only included the leisure theme, which contained phrases related to how
their best selves spent their free time or practiced different hobbies (e.g., “I had time to watch
TV series and movies”).
Features of the texts. In addition, the collected features of the compositions were: length
of the essay (total number of words), quantity of sensorial details (e.g., “I was drinking tea, it
tasted stronger than usual. I added sugar and started to blow, it was so hot . . . I could see the
steam coming out of the cup”), emotional valence of the essay, and incongruousness. Emo-
tional valence was calculated as the subtraction of the total number of positive emotional states
(e.g., “It was some years ago, but the feeling still lingers: pride”, “I feel vigorous, energetic, tol-
erant and strong”) minus the number of negative emotional states (e.g., “In my future I keep
seeing a lot of stress and anxiety”, “I feel pretty demotivated in my academic life”) in each text.
Regarding incongruousness, it was coded on phrases in which participants talked about a posi-
tive feature explicitly expressed as no longer present (e.g., “I have the feeling that I enjoyed the
little things more than I do now”), or the willingness to reduce or eliminate the presence of a
personal feature (e.g., “My best self would learn not to overthink everything, because right
now I brood a lot about everything”).
Finally, all essays were coded independently by two researchers (AC and MMS). Disagree-
ments were resolved by consensus and by consultation with a third researcher expert in the
field (RMB). Intercoder reliability was assessed with Kappa coefficients and correlations
between coders for all categories. Kappa values ranged from .78 to 1, and correlations ranged
from .87 to 1 (see Table 1). These results indicate high levels of agreement [28].
Data analyses
Analyses of the texts were carried out with ATLAS.ti software for Windows (v. 7.5.4). Statisti-
cal analyses were conducted using the SPSS software for Windows (v. 24). In order to test the
differences between conditions on the content and features of the texts, two multivariate analy-
sis of variance (MANOVAs) were carried out, one for the content themes and another for the
Qualitative analysis of the Best Possible Self
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text features. Pairwise comparisons using Bonferroni adjustment were conducted when signif-
icant differences were found among conditions. To examine the content themes and text fea-
tures that predicted the change in PA, a stepwise multiple regression analysis was conducted
entering the change in PA as dependent variable, and all themes and text features as indepen-
dent variables. Change in PA was calculated using pre-intervention PA scores and post-inter-
vention PA scores (i.e., change = post-intervention PA—pre-intervention PA), where positive
values for change in PA reflected an improvement. Finally, ten parallel multiple mediation
analyses (one for each theme) were performed in each condition to test whether the effect of
the content of the text on change in PA was mediated by the features of the text, using the pro-
cedure described by Hayes [29] from the PROCESS macro (version 2.16), choosing “model 4”.
In our proposed mediation models, we included the features of the texts as mediators in the
relationship between the themes of the essays and the change in PA. That is, we explored
whether the effects produced by the themes of the texts on the change in PA were mediated by
how these texts were written. These analyses were carried out for each condition. Bias-cor-
rected bootstrap 95% confidence intervals (CI) based on 5,000 samples were used to assess the
specific and total indirect effects. A CI that did not include the zero value indicated a signifi-
cant indirect effect, implying that the effect of the theme on the change in PA was mediated by
the features of the texts. Pairwise comparisons between specific indirect effects were carried
out to test whether one indirect effect was statistically different from another through the con-
fidence interval.
For both regression and mediation analyses, the frequency of participants who included
each theme and feature in their text was calculated for each condition. This was done as some
themes or features were especially uncommon in some conditions. Therefore, if a specific
Table 1. Kappa values and intercoder correlations.
Kappa values Correlation values
Themes of the texts
Personal area
Positive features .81 .97
Skills .78 .87
Health .88 .90
Academic/professional area
Intrinsic .78 .89
Extrinsic .91 .91
Social area
Friendship .78 .91
Family .91 .90
Partner .97 .92
Help .85 .92
Leisure area
Leisure .85 .92
Essay features
Positive emotional states .90 .98
Negative emotional states .80 .92
Incongruousness .90 .98
Sensorial details 1 1
Notes: For all correlations, p<.001. Positive and negative emotional states were subsequently used to calculate the
emotional valence of the texts.
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theme or feature appeared in less than 25% of the texts (that is, less than 7 participants of one
condition included it in their texts), it was considered that the theme/feature was no represen-
tative of the sample on that specific condition, and thus it was not included in the analyses of
that condition. For example, sensorial details were not included in the mediation analyses in
BPS condition as it appeared in less than 25% of the texts in this condition.
Results
Descriptive analyses of the themes
Means and standard deviations of each theme and feature of the texts on the different condi-
tions can be found in Table 2. Generally, the most frequent themes of the texts on the three
conditions taken together were positive features (M = 2.09, SD = 1.55), friendship (M = 1.18,
SD = 0.98), and intrinsic (M = 0.86, SD = 0.79), and the least frequent ones were skills
(M = 0.21, SD = 0.57), health (M = 0.28, SD = 0.45), partner (M = 0.37, SD = 0.58) and help
(M = 0.32, SD = 0.59). The mean valence of the essays taking all conditions was 2.21
(SD = 2.10).
Differences between conditions on the content of the texts
Table 2 shows the mean, standard deviations, and the MANOVA results for the effect of condi-
tion on the themes of the essays. The MANOVA revealed that, using Pillai’s trace, there was a
significant effect of condition on the presence of the different themes, V= 0.72, F(20, 134) =
3.79, p<.001, η
2p
= .36. According to Cohen’s indications [28], the effect size was large (η
2p
>
.14). Separate univariate ANOVAs revealed significant effects of condition on positive features,
skills,friendship,family and partner. No significant effects of condition were found on health,
help,leisure or on the academic/professional area, neither on intrinsic or extrinsic themes.
Post-hoc comparisons using Bonferroni adjustment revealed that, regarding personal area,
positive features were more frequent in BPRES than in BPAS and BPS, and skills appeared
more frequently in BPRES than in BPAS. Regarding social area, friendship was more frequent
Table 2. Means (M) and standard deviations (SD) for the themes of the essays per condition.
Themes BPAS
M (SD)
BPRES
M (SD)
BPS
M (SD)
TOTAL
M (SD)
ANOVA results Post-hoc comparisons
Personal area
P. features 1.52 (1.42) 3.04 (1.74) 1.77 (0.99) 2.09 (1.55) F(2, 75) = 8.50, p<.001, η
2p
= .185 BPRES >BPAS, p= .001; BPRES >BPS, p= .006
Skills 0.00 (0.00) 0.40 (0.71) 0.23 (0.65) 0.21 (0.57) F(2, 75) = 3.49, p= .036, η
2p
= .085 BPRES >BPAS, p= .027
Health 0.19 (0.40) 0.24 (0.44) 0.42 (0.50) 0.28 (0.45) F(2, 75) = 2.04, p= .137, η
2p
= .052 n.s.
Academic / professional area
Intrinsic 0.85 (0.72) 0.80 (0.87) 0.92 (0.80) 0.86 (0.79) F(2, 75) = .16, p= .857, η
2p
= .004 n.s.
Extrinsic 0.52 (0.58) 0.40 (0.65) 0.85 (0.78) 0.59 (0.69) F(2, 75) = 3.02, p= .055, η
2p
= .074 n.s.
Social area
Friendship 1.67 (1.33) 0.88 (0.67) 0.96 (0.53) 1.18 (0.98) F(2, 75) = 5.83, p= .004, η
2p
= .135 BPAS >BPRES, p= .009; BPAS >BPS, p= .020
Family 0.37 (0.56) 0.64 (0.64) 0.88 (0.65) 0.63 (0.65) F(2, 75) = 4.58, p= .013, η
2p
= .109 BPS >BPAS, p= .010
Partner 0.37 (0.69) 0.16 (0.37) 0.58 (0.58) 0.37 (0.58) F(2, 75) = 3.46, p= .036, η
2p
= .085 BPS >BPRES, p= .031
Help 0.22 (0.58) 0.20 (0.41) 0.54 (0.71) 0.32 (0.59) F(2, 75) = 2.77, p= .069 η
2p
= .069 n.s.
Leisure area
Leisure 0.56 (1.01) 0.31 (0.74) 0.65 (0.75) 0.49 (0.83) F(2, 75) = 1.74, p= .182, η
2p
= .044 n.s.
Notes: P. features = Positive features, n.s. = not significant.
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in BPAS than in BPRES and BPS, family was more frequent in BPS than BPAS, and partner
appeared more frequently in the texts in BPS than in BPRES.
Differences between conditions on the features of the texts
Table 3 shows the means, standard deviations, and the MANOVA results for the effect of
condition on the features of the essays. The MANOVA showed that, using Pillai’s trace, there
was a significant effect of condition on the presence of the features of the texts, V= 0.22,
F(8, 146) = 2.31, p= .023, η
2p
= .11. According to Cohen’s indications [28], the effect size was
moderate (η
2p
>.06).
Separate univariate ANOVAs and post-hoc analyses using Bonferroni adjustment revealed
that the number of sensorial details was higher in BPAS than in BPRES texts, and incongru-
ousness appeared significantly more often in BPS than in BPRES. A tendency to reach signifi-
cance on the effect of condition on the valence of the essays was found, being more positive in
BPAS than in BPS. No significant differences between conditions were found on length.
Analyses of the predictors of the change in PA: do the themes and features
of the texts predict the change in PA?
Three stepwise multiple regression analyses, one for each condition, were used to examine
which themes and features predicted change in PA. Variance Inflation Factor ranged from
1.00 to 1.01, indicating no problems with multicollinearity [30,31]. All the themes and features
were entered simultaneously. For BPAS, only emotional valence remained as a significant pre-
dictor of change in PA (β= 0.84, t= 2.84, p= .009). The model was statistically significant,
F(1,25) = 8.05, p= .009, R
2
= .24, R
2Adjusted
= .21, explaining 21% of the variance. By contrast,
for BPS, length of the essay (β= 0.02, t= 2.07, p= .050) and extrinsic theme (β= 3.71, t= 3.02,
p= .006) remained as significant predictors of change in PA. The model was statistically signif-
icant, F(1,23) = 4.29, p= .050, R
2
= .39, R
2Adjusted
= .34, explaining 34% of the variance in PA.
In the case of BPRES, none of the variables remained as significant predictors.
Parallel multiple mediation analyses: do the features of the texts mediate
the relationship between the themes of the texts and the change in PA?
Coefficients, Standard Errors (SE) and Confidence Intervals (CI) of the parallel multiple medi-
ations for the significant models can be found in Table 4.
In BPAS condition, there were significant indirect effects of friendship and partner on
change in PA through emotional valence, b= 0.76, 95% CI [0.22, 1.95] and b= 0.98, 95% CI
[0.06, 3.29], respectively (see Fig 1), as bias-corrected bootstrap 95% confidence intervals (CI)
for the indirect effects, based on 5.000 bootstrap samples, did not included zero. Neither the
total effect, b= -0.97, t = -2.02, p= .056, nor the direct effect, b= -0.55, t= -1.02, p= 0.319
Table 3. Means (M) and standard deviations (SD) for the features of the essays per condition.
Essay features BPAS
M (SD)
BPRES
M (SD)
BPS
M (SD)
TOTAL
M (SD)
ANOVA results Post-hoc comparisons
Valence 2.96 (2.14) 1.92 (1.98) 1.69 (2.00) 2.21 (2.10) F(2,75) = 2.93, p= .060, η
2p
= .072 BPAS >BPS, p= .079
1
Incongruousness 0.19 (0.62) 0.04 (0.20) 0.77 (1.61) 0.33 (1.04) F(2,75) = 3.81, p= .027, η
2p
= .092 BPS >BPRES, p= .034
Sensorial details 0.63 (1.21) 0.04 (0.20) 0.15 (0.78) 0.28 (0.88) F(2,75) = 3.54, p= .034, η
2p
= .086 BPAS >BPRES, p= .045
Length 278.78 (92.97) 252.04 (83.05 249.15 (89.85) 260.33 (88.73) F(2,75) = 0.87, p= .412, η
2p
= .023 n.s.
Notes:
1
= marginally significant, n.s. = not significant.
https://doi.org/10.1371/journal.pone.0216896.t003
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were significant. No significant indirect effects were found for the rest of the themes and fea-
tures, as all CI included zero. Thus, results imply that, when participants in BPAS condition
wrote about the themes friendship and partner, they wrote more positive texts (i.e., with higher
emotional valence), and that produced higher changes in PA.
Regarding BPRES, no significant indirect effects were found, as all CI included zero and all
p>.05.
For BPS, there were significant indirect effects of positive features and family on change in
PA through length (i.e., number of words), b= 1.20, 95% CI [0.13, 3.95], and b= 2.83, 95% CI
[0.50, 7.64] respectively, given that bias-corrected bootstrap 95% confidence intervals (CI) for
Table 4. Coefficients, Standard Errors (SE) and Confidence Intervals (CI) of the parallel multiple mediations for the significant models.
BPAS condition BPS condition
Friendship as predictor Partner as predictor P.features as predictor Family as predictor
Coefficients (SE) 95% CI Coefficients (SE) 95% CI Coefficients (SE) 95% CI Coefficients (SE) 95% CI
Indirect effects
Total indirect effect 1.25 (0.59) [0.28, 2.78] 0.86 (0.94) [-0.96, 2.75] 0.73 (0.97) [-0.80, 3.29] 3,30 (1,68) [0.78, 7.89]
S.P. in Valence 0.76 (0.38) [0.22, 1.94] 0.98 (0.67) [0.06, 3.29] -0.14 (0.39) [-1.39, 0.36] 0.07 (0.38) [-0.37, 1.39]
S.P. in Length 0.09 (0.39) [-0.26, 1.40] -0.01 (0.19) [-0.61, 0.14] 1.20 (0.80) [0.13, 3.95] 2.83 (1.62) [0.50, 7.64]
S.P. in Sensorial details 0.40 (0.38) [-0.15, 1.23] -0.10 (0.52) [-2.13, 0.48] - - - -
S.P. in Incongruousness - - - - -0.33 (0.44) [-1.82, 0.16] 0.41 (0.62) [-0.10, 2.62]
Contrasts
Valence–Length 0.67 (0.59) [-0.18, 1.70] 0.99 (0.72) [0.06, 3.43] -1.33 (0.97) [-4.31, -0.02] -2.75 (1.73) [-7.76, -0.29]
Valence–Sensorial details 0.35 (0.59) [-0.48, 1.80] 1.07 (0.75) [0.02, 3.40] - -
Length–Sensorial details -0.31 (0.53) [-1.28, 0.76] 0.08 (0.56) [-0.80, 1.64] - -
Valence–Incongruousness - - - - 0.19 (0.62) [-0.91, 1.61] -0.33 (0.71) [-2.26, 0.57]
Length–Incongruousness - - - - 1,53 (0.84) [0.30, 3.96] 2.42 (1.76) [-0.28, 7.45]
Notes: “Incongruousness” was not included in the analyses in BPAS condition as it appeared in less than 25% of the texts in this condition, and the same procedure was
followed for “Sensorial details” in BPS condition. P. features = Positive features. S.P. = Specific change
https://doi.org/10.1371/journal.pone.0216896.t004
Fig 1. Parallel multiple mediations between content themes and change in PA throughfeatures of the texts in BPAS condition. Notes: All coefficients
represent unstandardized regression coefficients (and standard error in parenthesis). �p<.05; �� p<.01; ��� p<.001. PA = Positive affect.
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the indirect effects, based on 5.000 bootstrap samples, did not include zero (see Fig 2). Again,
neither the total effect, b= 1.38, t = 1.52, p= 0.141, nor the direct effect, b= 0.63, t= 0.71,
p= 0.488 were significant. No significant indirect effects were found for the rest of the themes
and features, as all CI included zero. These results suggest that, when participants in BPS con-
dition wrote about their positive features or family, they wrote longer texts, and that produced
higher changes in PA.
Discussion
This study showed that, despite the similar effects produced by writing about one’s best self in
the past, present or future on positive mood [13], these interventions respond to different
underlying mechanisms. The procedure of the included PPIs was identical (to write about the
best version of oneself), and the only difference between them was the time frame in which
participants had to focus on: their past, present or future. Notably, significant differences were
found in the content on the compositions depending on the condition. When writing about
their best past self (BPAS), participants more frequently included their social relationships
with their friends than the other conditions. In addition, they added more sensorial details
than the ones who wrote about their present self, which goes in line with previous studies that
suggest that recalling past events exhibit more sensorial details than imagining future events,
as the latter needs more mental work to supply these [32,33]. In the case of participants who
wrote about their best present self (BPRES), they talked more frequently about their personal
area, including their skills more often than in the past condition, and their positive features
more often than the rest of the conditions. Lastly, when participants wrote about their best
possible self in the future (BPS), their texts focused more on their familial relationships, being
their family more frequently included than in the past condition, and their partner more fre-
quently than in the present condition. In addition, they included more incongruousness in
their essays comparing with the present condition. Some of these results are in consonance
with previous studies about self-descriptions, which showed that participants’ descriptions of
their current self are more focused on oneself, followed by their past self-descriptions and least
of all their future self-descriptions, which were more socially oriented [34].
Fig 2. Parallel multiple mediations between content themes and change in PA throughfeatures of the texts in BPS condition. Notes: All coefficients
represent unstandardized regression coefficients (and standard error in parenthesis). �p<.05; �� p<.01; ��� p<.001. PA = Positive affect.
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As regards to predictions of change in PA, emotional valence arose as a significant predictor
of change in PA in the BPAS texts, whereas the length of the essay and academic or profes-
sional theme extrinsically motivated remained as significant predictors of change in PA for
participants in the BPS condition. That is, when writing about their best past self, the more
positive the compositions participants wrote, the better results on their levels of positive mood
they obtained. Conversely, when writing about their best possible self in the future, the more
words participants wrote, or the more they included the extrinsic academic or professional
theme, the more benefits they achieved on their positive mood levels. In the case of present
condition, none of the variables remained as significant predictors.
With respect to mediation analyses, significant indirect effects of friendship and partner on
PA change through emotional valence in the case of BPAS were found. For the BPS condition,
significant indirect effects of text length on PA change through positive features and family. In
other words, when participants wrote about their past self and talked about their relationship
with their friends or their partners, this led to greater positivity in their texts, which produced
improvements in their levels of positive mood. In the case of participants who wrote about
their best possible self in the future, when they focused on their own positive features or their
relationships with their family, this produced longer texts, which led to better results in their
levels of positive emotions. In the case of participants who wrote about their best current self,
no indirect effects were found.
Based on these results, it is possible to conclude that there are differences in the content and
form of the compositions of the three PPIs as well as their underlying mechanisms: even that
all of them consisted of writing about their best selves, the themes and features of their essays
were different, and the factors that predicted and mediated the change in the level of positive
mood were also different. It seems that positive emotional valence in combination with social
themes as friendship or partner play an important role in the BPAS condition, whereas the
length of the essay combined with positive features or family have an impact on the efficacy of
the BPS condition. It is worth to note, however, that the analyses did not find significant results
on the BPRES condition.
These results can have important implications. Approaching to disentangle the working
mechanisms of psychological interventions can help practitioners to use the interventions to
their most potential. In this sense, the results obtained in this specific study may help to boost
the effects of the interventions by, for example, modifying or highlighting specific features in
the instructions. Since emotional valence seems to be a key component of the BPAS condition,
it could be beneficial to encourage participants to include as many positive emotional states as
possible when they write about their best past self. However, some participants can feel frus-
trated if they are not able to naturally include positive emotional states when they are asked to
do so. In this case, and based on the results on the mediation analyses, emphasizing the social
area (writing about their friends or partner) could indirectly boost the efficacy of this PPI. Fol-
lowing the same rationale, the length of the text is an important factor in the future condition.
It is possible to encourage participants to write down as much as possible. However, it is not
feasible to know how much they should write, and it is possible that some discomfort reactions
could arise in a participant who does not accomplish to write as much as asked. In the same
manner, after mediation analyses results, asking participants to focus on their positive features
and family relationships in their texts could indirectly amplify the efficacy of the intervention.
This study has some limitations that are necessary to address. First, the sample included
was considerably young (M = 20.23, SD = 4.10). Even though this is not a limitation per se,
including a sample with more heterogeneous age could have helped us to produce more gener-
alizable results. In addition, it would be highly interesting to conduct future studies in a more
heterogeneously aged sample, in order to explore whether older participants show the same
Qualitative analysis of the Best Possible Self
PLOS ONE | https://doi.org/10.1371/journal.pone.0216896 May 17, 2019 12 / 15
pattern as the younger ones. Second, we were not able to find which mechanisms underlie in
the efficacy of writing about one’s present best self (BRES). It is possible that the term “present
self” seemed too broad to participants, which led to an excessively heterogeneous time range to
find significant results. Previous research has found that there are significant differences
between recalling near and far past events, as well as between imagining near or far future
events [33,35]. Participants writing about their best self in the present could have focused on
their present moment, but it is also possible that some of them included near past or even
future time frames, as it was not predefined in the instructions, thus different processes may
have been affecting on this condition. Future studies should explore this condition in more
detail, either encouraging participants to focus on a specific time frame or exploring which
time range they included in their texts.
This work has been the first attempt to study which are the underlying mechanisms of the
BPS intervention and the two variants derived from it, and the role that these mechanisms
have on their efficacy. There is evidence about PPIs being efficacious resources to improve
wellbeing over different populations, but the research about the mechanisms that produce
those benefits is still in its infancy [5,12,13]. Hence, there is still much more to investigate in
this regard. This study helped to shed light on the importance of the idiosyncratic features of
PPIs in order to better understand how they work. Results obtained provide a richer knowl-
edge about the process that takes part when participants practice the BPS intervention and its
temporal variants. This deeper understanding can be a powerful tool to increment their effi-
cacy by, for example, modifying the instructions of the exercises. We encourage researchers to
continue the investigations on this topic, as a better knowledge about why and how PPIs work
will help psychologists and other professionals to make the most of these valuable resources.
Acknowledgments
CIBERobn is an initiative of the ISCIII.
Author Contributions
Conceptualization: Alba Carrillo, Marian Martı
´nez-Sanchis, Rosa M. Baños.
Formal analysis: Alba Carrillo, Marian Martı
´nez-Sanchis.
Investigation: Alba Carrillo, Marian Martı
´nez-Sanchis, Ernestina Etchemendy.
Methodology: Alba Carrillo, Marian Martı
´nez-Sanchis, Rosa M. Baños.
Supervision: Ernestina Etchemendy, Rosa M. Baños.
Writing – original draft: Alba Carrillo, Marian Martı
´nez-Sanchis.
Writing – review & editing: Ernestina Etchemendy, Rosa M. Baños.
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