AbstractIt is often the case that one can choose a mix of alternative options rather than have to select one option only. Such an opportunity to diversify may blunt the risk involved in all-or-none choice. Here we investigate repeated investment decisions in two-valued options that differ in their riskiness, looking for the effects of recent decisions and their outcomes on upcoming decisions. We compare these effects to those evident in all-or-none choice between the same risky options. The

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... te of the world", namely, the likelihood of the high versus the low outcomes of the options, is manipulated. We find that aggregate allocation diverges from uniformity (i.e., from 1/n), and is sensitive to outcome probabilities, with the pattern of results indicating reactivity to the outcome of the previous decision. Round-to-round dynamics reveal that the outcome of the previous decision has an effect on the subsequent decision, on top of inertia; the aspects of the outcome that influence the next decision indicate an effect of a missed opportunity, if there was one, in the previous decision. Importantly, recent outcomes have a similar effect in diversification decisions and in all-or-none choice.