The Case for Repeated Measures in Ergonomic Experiments: Another Look

Abstract

Repeated measures designs have been suggested as being inappropriate in most ergonomic research because of the presence of unwanted order effects which bias the results. Poulton has discussed a number of studies in several areas in which such order effects have rendered the interpretation of the results unreliable. The present study investigated order effects by combining in a single experiment a between-subjects design and a within-subjects design. Eight subjects were exposed to four combinations of two stressors, noise and ice-pressor, in a character recognition task based on reaction time measures. The experimental layout included order as an independent variable and found a significant main effect for treatments (F = 10.89, p < .005). More importantly treatments were found to interact with order (F = 3.26, p < .05). Because of the economy of repeated measures designs in terms of subject number, it is suggested that rather than categorically abandoning their use, research should be undertaken to determine: (1) if order effects are always present; (2) with what variables and combinations of variables they occur; (3) the consistency of such effects in terms of magnitude and direction; and (4) the practical as well as the statistical significance of particular order effects. In addition, the issues of individual differences and intra-subject consistency are discussed in relation to repeated measures designs. Finally, it is suggested that the discrimination of those situations where repeated measures designs can be used effectively is a more practical and fruitful activity than the wholesale elimination of repeated measures from erogomics research.

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References

Bensel

C. K.

Lockhart

J. M.

Cold-induced vasodilatation onset and manual performance in the cold. Ergonomics, 1974, 17, 717–730.

Cohen

H. H.

Conrad

D. W.

O'Brien

J. F.

Pearson

R. G.

Noise effects, arousal, and human information processing task difficulty and performance. Raleigh, North Carolina: North Carolina State University, 1973.

Glass

D. C.

Singer

J. E.

Urban stress: Experiments on noise and social stressors. New York: Academic Press, 1972.

Kirk

R. E.

Experimental design: Procedures for the behavioral sciences. Belmont, California: Brooks/Cole Publishing Co., 1968.

Lacey

J. I.

Van Lehn

Differential emphasis in somantic response to stress: An experimental study. Psychosomatic Medicine, 1952, 14, 71–81.

Lindquist

E. F.

Design and analysis of experiments in psychology and education. Boston: Houghton Mifflin Co., 1953.

Pearson

R. G.

Alcohol-hypoxia effects upon operator tracking, monitoring, and reaction time. Aerospace Medicine, 1968, 39, 303–307.

Poulton

E. C.

Bias in ergonomic experiments. Applied Ergonomics, 1973a, 4, 17–18.

Poulton

E. C.

Unwanted range effects from using within-subject experimental designs. Psychological Bulletin, 1973b, 80, 113–121.

10.

Poulton

E. C.

Range effects are characteristic of a person serving in a within-subjects experimental design - a reply to Rothstein. Psychological Bulletin, 1974, 81, 201–202.

11.

Poulton

E. C.

Range effects in experiments on people. American Journal of Psychology, 1975, 88, 3–32.

12.

Poulton

E. C.

Edwards

R. S.

Interaction and range effects in experiments on pairs of stressors: Mild heat and low frequency noise. Journal of Experimental Psychology, 1974a, 102, 621–628.

13.

Poulton

E. C.

Edwards

R. S.

Interactions, range effects, and comparisons between tasks in experiments measuring performance with pairs of stresses: Mild heat and one mg. of L-hyoscine hydrobromide. Aerospace Medicine, 1974b, 45, 735–741.

14.

Poulton

E. C.

Edwards

R. S.

Colquhoun

W. A.

The interaction of loss of a night's sleep with mild heat: Task variables. Ergonomics, 1974, 17, 59–73.

15.

Rothstein

L. D.

Reply to Poulton. Psychological Bulletin. 1974, 81, 199–200.

16.

Simon

C. W.

Methods of handling sequence effects in human factors engineering experiments. Springfield, Virginia: National Technical Information Service, December 1974. (AD/A-006 240).