Individual Differences in Response to the Environment

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Abstract
In assessing the effects of environmental stress three points are made. 1. Comfort and working efficiency cannot necessarily be equated. 2. The optimal experimental design for assessing individual differences differs fundamentally from that required for establishing population means. Reliable individual differences will only be revealed by repeated measures of a given effect upon the same people and under the same conditions. 3. Regarding the assessment of what individuals find comfortable as regards temperature, or acceptable as regards noise, two difficulties are noted, (a) In terms of what they are prepared to do about it individuals may differ in what they mean when they tick one of a number of terms indicating varying degrees of discomfort or annoyance. (b) Where an observer experiences a range of conditions he will tend to place the centre point of the rating scale at the centre of the range of conditions sampled. Over a group of observers this may bias the average comfort or acceptability vote away from its true point. It may also artefactually increase the variation between individuals who receive conditions in different orders of presentation, On the other hand differences between groups of observers, for example young and old, may be minimised if the same range of conditions is presented to all. The presentation of a standard followed by a single test condition will avoid difficulties due to range effects but may encounter others due to suggestion or contrast effects.