Pretest-posttest_design

Pretest-posttest_design - Work 20 (2003) 159165 IOS Press...

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Work 20 (2003) 159–165 159 IOS Press Speaking of Research Pretest-posttest designs and measurement of change Dimiter M. Dimitrov and Phillip D. Rumrill, Jr. 507 White Hall, College of Education, Kent State University, Kent, OH 44242-0001, USA Tel.: +1 330 672 0582; Fax: +1 330 672 3737; E-mail: ddimitro@kent.edu Abstract . The article examines issues involved in comparing groups and measuring change with pretest and posttest data. Different pretest-posttest designs are presented in a manner that can help rehabilitation professionals to better understand and determine effects resulting from selected interventions. The reliability of gain scores in pretest-posttest measurement is also discussed in the context of rehabilitation research and practice. Keywords: Treatment effects, pretest-posttest designs, measurement of change 1. Introduction Pretest-posttest designs are widely used in behav- ioral research, primarily for the purpose of comparing groups and/or measuring change resulting from exper- imental treatments. The focus of this article is on com- paring groups with pretest and posttest data and related reliability issues. In rehabilitation research, change is commonly measured in such dependent variables as employment status, income, empowerment, assertive- ness, self-advocacy skills, and adjustment to disabil- ity. The measurement of change provides a vehicle for assessing the impact of rehabilitation services, as well as the effects of specific counseling and allied health interventions. 2. Basic pretest-posttest experimental designs This section addresses designs in which one or more experimental groups are exposed to a treatment or in- tervention and then compared to one or more control groups who did not receive the treatment. Brief notes on internal and external validity of such designs are first necessary. Internal validity is the degree to which the experimentaltreatment makes a differencein (or causes change in) the specific experimental settings. External validity is the degree to which the treatment effect can be generalized across populations, settings, treatment variables, and measurement instruments. As described in previous research (e.g. [11]), factors that threaten in- ternal validity are: history, maturation, pretest effects, instruments, statistical regression toward the mean, dif- ferential selection of participants, mortality, and in- teractions of factors (e.g., selection and maturation). Threats to external validity include: interaction effects of selection biases and treatment, reactive interaction effect of pretesting, reactive effect of experimental pro- cedures, and multiple-treatment interference. For a thorough discussion of threats to internal and external validity, readers may consult Bellini and Rumrill [1]. Notations used in this section are:
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Pretest-posttest_design - Work 20 (2003) 159165 IOS Press...

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