Time resolution of clocks: Effects on reaction time measurement—Good news for bad clocks

Abstract

This paper investigates the measurement of reaction times (RTs) with clocks of limited time resolution. The questions raised are: (a) What is the relationship between measured and true RT? (b) Are mean and variance of measured RT biased, and if so, (c) how does this bias depend on the clock's time resolution? (d) Is it possible to correct this bias? It is concluded that the bias is practically negligible even if the time resolution of a clock is only 30 ms. The results show that a clock of limited time resolution biases mean and variance of measured RT. Furthermore it is shown that the effect of time resolution on detecting a true mean RT difference is negligible if the variance of true RT is relatively large. Formulae are provided to correct the bias of mean and variance of measured RT. In addition the implication of time resolution on measured RT for paired observations is analysed. It is shown that the product moment correlation coefficient but not the covariance of paired RT measures is affected by time resolution. A correction formula to remove the bias on the product moment correlation coefficient is provided.

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