The advantages and disadvantages of repeated measures
Repeated measures are the method of using the same participants in different experimental manipulations (Field, 2011). This is in contrast to independent groups in which different groups of participants are exposed to just one experimental condition (Howitt & Cramer, 2011). Repeated measures, in using the same participants for both manipulations, allow the researcher to exclude the effects of individual differences that could occur in independent groups (Howitt & Cramer, 2011). Factors such as IQ, ability, age and other important variables remain the same (Field, 2011). This is a strength of repeated measures and one of the greater disadvantages of independent group methods. As the same participants are used, it requires fewer participants than the independent group as independent need an equal minimum number of different participants for each situation (Howitt & Cramer, 2011). This makes successfully recruiting the necessary number of participants quicker and easier in repeated measures.
Although these strengths favour repeated over independent groups, independent has strengths where repeated measures weaken. The use of the same participants leads to difficulties counteracting problems of order effects and the need for additional materials. An effect observed in results could therefore be due to boredom affecting concentration and performance such as reaction time, and accuracy caused by repetition (Pan, Shell & Schleifer, 1994; Bergh & Vrana, 1998). Effects could also be due to practice causing participants’ results to improve because they were given more chance to practice and become familiar with the task (Collie, Maruff, Darby & McStephen, 2003). The order effects of an experiment can be reduced by counterbalancing (Field, 2011). This involves randomly assigning the order of the experimental manipulations participants are exposed to. For example half the participants would be exposed to control A first and then control B, and the other half of participants exposed to control B and then control A (Howitt & Cramer, 2011). The results collected should then be less affected by factors such as boredom and practice. Researchers can also provide opportunities to take a break during the experiment to counteract boredom and loss of concentration (Pan, Shell & Schleifer, 1994).
If a study was testing how Factor A and Factor B affected memory the researcher would require a different list of words for participants to memorise for Factor A and B, whereas in independent groups the same list could be used for each factor because each group only sees the material once (Nilsson, Soli & Sullivan, 1994). In using repeated measures the individual differences of participants is reduced but this instead produces problems with individual differences between the materials or environments the participants are exposed to. Therefore the result may be due to these differences in materials rather than the independent variable in question. The materials must be carefully examined to ensure equal quality in factors such as difficulty (Riedel, Klaassen, Deutz, Someren & Praag, 1999).
The advantages and disadvantages of repeated measures must be compared with the benefits of using independent groups. Each study must have careful consideration into which design would best meet the needs of the study. Problems related to the design must be reduced to have as little effect on results as is possible. Both methods are not without difficulty and the researcher must decide which would best produce results the investigation is studying.
Bergh, O. V., & Vrana, S. R. (1998). Repetition and boredom in a perceptual fluency/ attributional model of affective judgements. Cognition and Emotions, 12, 533-553. doi: 10.1080/026999398379556
Collie, A., Maruff, P., Darby, D. G., & McStephen, M. (2003). The effects of practice on the cognitive test performance of neurologically normal individuals assessed at brief test-retest intervals. Journal of the International Neuropsychological Society, 9, 419-428. doi: 10.1017/S1355617703930074
Field, A. (2011). Discovering Statistics Using SPSS. (3rd ed.). (pp. 15-18).Thousand Oaks,California: SAGE Publications
Howitt, D., & Cramer, D. (2011). Introduction to Research Methods in Psychology. (3rd ed.). (pp. 164, 179-181). Harlow, Essex: Pearson Education Limited
Nilsson, M., Soli, S. D., & Sullivan, J. A. (1994). Development of hearing in noise test for the measurement of speech reception thresholds in quiet and in noise. Journal of the Acoustical Society of America, 95, 1085-1099. [Abstract] Retrieved from http://asadl.org/jasa/resource/1/jasman/v95/i2/p1085_s1?isAuthorized=no
Pan, C. S., Shell, R. L., & Schleifer, L. M. (1994). Performance variability as an indicator of fatigue and boredom effects in a VDT data-entry task. International Journal of Human-Computer Interaction, 6, 37-45. doi: 10.1080/10447319409526082
Riedel, W. J., Klaassen, T., Deutz, N. E. P., Someren, A., & Praag, H. M. (1999). Tryptophan depletion in normal volunteers produces selective impairment in memory consolidation. Psychopharmacology, 141, 362-369. doi: 10.1007/s002130050845