Judgments of the Relative Frequency of Two Random Sequential Events: Effects of Duration of Observation

Dwight E. Erlick

Jan 1960 · Wright Air Development Division

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"The purpose of this investigation was to determine the effect that duration of observation has on one's ability to tell which of two random sequential events has occurred more frequently. Using a rate of four events per second and observation durations ranging from 1.75 to 80 seconds, two specific conditions were studied: (1) the effect of having a constant observation period repeated so that subjects could anticipate the duration of each observation, and (2) the effect of having a highly variable observation time such that the observer could not accurately anticipate when the time sample would end. Using 75 per cent correct identification of the more frequent event as a threshold measure, the results indicate, for both presentation conditions, that a smaller increment in frequency of one of the events over the other was needed as the observation duration increased. An asymptote was reached as the ratio between the more frequent and the less frequent event approached 1.20. With a constant observation time, the asymptote is reached between 10 and 20 seconds duration, while with a variable observation time, it is reached between 40 and 80 seconds."--Abstract