Date of Award

Summer 7-31-2017

Degree Type


Degree Name

MS Experimental Psychology




Kelly Goedert, Ph.D

Committee Member

Michael Vigorito, Ph.D

Committee Member

Bob Rehder, Ph.D


outcome density effect, cognitive demand


Judgments regarding the strength of a cause to produce an outcome do not always follow predictions of normative causal reasoning models (Kao & Wasserman, 1993). In the case of the outcome density effect, individuals’ ratings of the strength of a putative cause tend to be greater when the number of observed outcomes is high than when it is low (e.g. Jenkins & Ward, 1965). In the current experiment, I investigated the outcome density effect as a possible heuristic. Participants made causal judgments based on information about the prevalence of headaches in a sample of individuals who did or did not receive a mineral. To manipulate cognitive load, stimuli differed in sample size (n = 24 or 72) and presentation format (scrambled or organized information). Although each stimulus depicted a non-contingent relationship, there were pervasive outcome density effects for causal judgments in each condition. However, the probability of the outcome had no effect on estimates of causal power, suggesting the importance of how causal questions are worded. Manipulations of cognitive load did not influence the magnitude of the outcome density effect for causal judgments or affect causal power estimates. Thus, the outcome density effect does not appear to be used as a heuristic in tasks that vary in cognitive demand, at least as manipulated by sample size and the organization of information.