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Toolbox or Adjustable Spanner? A Critical Comparison of Two
Metaphors for Adaptive Decision Making
Anke Söllner and Arndt Bröder
University of Mannheim
For multiattribute decision tasks, different metaphors exist that describe the process of decision making
and its adaptation to diverse problems and situations. Multiple strategy models (MSMs) assume that
decision makers choose adaptively from a set of different strategies (toolbox metaphor), whereas
evidence accumulation models (EAMs) hold that a uniform mechanism is employed but is adapted to the
environmental change (adjustable spanner metaphor). Despite recent claims that the frameworks are hard
to disentangle empirically, both metaphors make distinct predictions concerning the information acqui-
sition behavior, namely, that search is terminated according to the selected strategy (MSMs) or that
information is acquired until an evidence threshold is passed (EAMs). In 3 experiments, we contrasted
these predictions by providing participants with different degrees of evidence in a half-open/half-closed
information board. For the majority of participants, we find that their stopping behavior is well captured
by the notion of an evidence threshold that is either undercut or passed by the given evidence.
Keywords: decision making, evidence accumulation, information board, single-process models,
multiple-strategy models
Supplemental materials: http://dx.doi.org/10.1037/xlm0000162.supp
When choosing between multiple options, decision makers
sometimes rely on one good reason only, and sometimes they
search for a lot of arguments before making their decision. Ob-
serving these adaptations, one can conclude that humans employ
different decision strategies in different situations (toolbox meta-
phor; e.g., Gigerenzer, Todd, & the ABC Research Group, 1999;
Payne, Bettman, & Johnson, 1993). But the behavioral changes
can also be explained by assuming that a uniform mechanism is
used, with its parameters adapted to the situation at hands (adjust-
able spanner metaphor; e.g., Lee & Cummins, 2004;Newell,
2005). These two metaphors or frameworks of decision making
coexist, primarily because they are both able to account for the vast
majority of empirical findings, but also because they are hard to
disentangle empirically (Jekel, 2012;Newell, 2005;Newell &
Bröder, 2008).
1
In the current article, we concentrate on predic-
tions from the two frameworks concerning the termination of
information acquisition and contrast them in a novel paradigm that
systematically varies the level of given evidence.
The remainder of this introduction is organized as follows: First,
we introduce the aforementioned two frameworks of decision
making in more detail. We then address the question of why
disentangling these coexisting approaches poses an “empirical
challenge” (Newell, 2005, p. 13) and give a brief overview of
recent attempts to tackle this task. Finally, we introduce a novel
paradigm that enables us to contrast the two frameworks by
concentrating on their predictions concerning the termination of
information acquisition under varying levels of given evidence.
This paradigm constitutes the basis for the three experiments
reported and discussed in the remainder of this article.
Two Frameworks of Decision Making
The two frameworks we will describe in turn address multiat-
tribute decision tasks. Here, among two or more options (e.g.,
potential oil drilling sites), decision makers have to choose the one
that scores highest on a certain criterion (e.g., quantity of contained
oil). As decision aids, attributes (or cues) that evaluate the options
can be consulted (e.g., a chemical analysis yielding a positive or
negative evaluation), and each cue has some validity in reference
to the decision criterion (e.g., a validity of .80 means that in eight
of 10 cases in which the chemical analysis discriminates, it favors
the site that actually contains the most oil). If the criterion is an
objective one (e.g., the quantity of oil), the task is referred to as
probabilistic inference, whereas a subjective criterion (e.g., pref-
erence for a day trip) characterizes a preferential choice task.As
empirical similarities suggest similar cognitive processes in both
domains (Bröder & Newell, 2008;Payne et al., 1993;Todd,
1
In this article, we focus on descriptive analyses, that is, the question of
whether empirical data are well accounted for by different models. Pre-
scriptive analyses, in contrast, concentrate on the question whether a
process complies with a normative standard, for example, whether a
specific decision strategy leads to a high percentage of correct decisions
given a certain environmental structure (e.g., Czerlinski, Gigerenzer, &
Goldstein, 1999;Gigerenzer & Brighton, 2009;Hogarth & Karelaia, 2006)
or under which environmental regularities limited search is justified (Lee &
Zhang, 2012).
This article was published Online First August 10, 2015.
Anke Söllner and Arndt Bröder, School of Social Sciences, University of
Mannheim.
The authors would like to thank Tilmann Betsch, Andreas Glöckner, and
Benjamin Hilbig for helpful comments on earlier drafts of this article.
Correspondence concerning this article should be addressed to Anke
Söllner, University of Mannheim, L13, 17, D-68131 Mannheim, Germany.
E-mail: anke.soellner@uni-mannheim.de
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Learning, Memory, and Cognition © 2015 American Psychological Association
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