A FURTHER STUDY OF ESTIMATING AVERAGES

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Abstract
An investigation is described of the types of averaging response made to several volues of a variable when these nre presented symbolically or graphically. Symbolic information was presented to subjects on small white cards on which were typed either 10 or 20 two-digit numbers. Graphical information was presented as 10 or 20 points on inch ruled tenths graph paper. Sets of data differed according to whether they were normally or skew distributed about the arithmetic mean value, and in the extent of scatter about the mean. The results confirmed previous work in showing that error of judgment increased as scatter increased, and to a greater extent with symbolic than "with grnphical material. Error was also greater with skew than with normal information. Comparison between the results obtained with the two types of distribution showed that the previously reported finding that error also increased with increasing amount of information was incorrect and was duo to inadequate experimental control of scatter for different amounts of information. Analysis of individual performances showed that subjects' responses differed in type and that their introspective reports related to their performance. In particular the proportion of judgments which could be classed as of ' arithmetic mean ' type varied significantly with the methods described. Further experiments are suggested to try to discover which of two possible models of mental averaging is correct and why error increased with increased scatter in the information.

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