ESTIMATING AVERAGES

Abstract

An investigation is described of ability to estimate averages of several values of a variable presented either symbolically or graphically. Symbolic information was presented to subjects on small white cards on which were typed between 10 and 20 two-digit numbers, Graphical information was presented as 10 to 20 points on inch, ruled tenths, graph paper. In most cases described, subjects wore allowed ten seconds to examine the information for judgement. With symbolic information they were allowed unlimited time after this in which to form a judgement, but with graphical information the examination time included the setting of a cursor line at a position across the graph corresponding to the judged average value. The information presented varied not only in amount but also in scatter of the values about their mean. The results show that for both symbolic and graphical information, the error of judgement increases with increasing amount and scatter of material presented. The effects of increasing amounts of information are much more marked with high scatter than with low scatter material. Differences between subjects were negligible amongst students but were pronounced among a group of chemical process operators. Scatter was much the most important variable affecting averaging accuracy and some interesting results were obtained when the material presented contained one item markedly different in value from its fellows. The results are discussed and further experiments are suggested to increase an understanding of the mechanisms of statistical judgements.

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