Causal judgements about temporal sequences of events in single individuals

Stimuli were presented in which values of an outcome variable for a single individual were recorded over 24 time periods, and an intervention was introduced at one of the time periods. Participants judged whether and how much the intervention affected the outcome. Judgements were affected by manipulations of the temporal relation between the intervention and a gradual increase in values on the outcome variable, by the size of the increase, by the time taken for the increase to occur, and by variance in the preincrease data. Most results were predicted by a simple model in which the mean outcome value for the preintervention time periods is subtracted from the mean outcome value for the postintervention time periods, though there was also an effect of temporal contiguity that is not predicted by the simple model. This form of information, which is a kind of quasiexperimental design, is more representative of the kind of information generally available for causal judgement than the more commonly investigated binary variables in which the cause is either present or absent, and the outcome either occurs or does not; as such, it is more revealing of how causal judgements are made under the conditions that prevail in the world.