Establishing the internal and external validity of experimental studies
ABSTRACT The information needed to determine the internal and external validity of an experimental study is discussed. Internal validity is the degree to which a study establishes the cause-and-effect relationship between the treatment and the observed outcome. Establishing the internal validity of a study is based on a logical process. For a research report, the logical framework is provided by the report's structure. The methods section describes what procedures were followed to minimize threats to internal validity, the results section reports the relevant data, and the discussion section assesses the influence of bias. Eight threats to internal validity have been defined: history, maturation, testing, instrumentation, regression, selection, experimental mortality, and an interaction of threats. A cognitive map may be used to guide investigators when addressing validity in a research report. The map is based on the premise that information in the report evolves from one section to the next to provide a complete logical description of each internal-validity problem. The map addresses experimental mortality, randomization, blinding, placebo effects, and adherence to the study protocol. Threats to internal validity may be a source of extraneous variance when the findings are not significant. External validity is addressed by delineating inclusion and exclusion criteria, describing subjects in terms of relevant variables, and assessing generalizability. By using a cognitive map, investigators reporting an experimental study can systematically address internal and external validity so that the effects of the treatment are accurately portrayed and generalization of the findings is appropriate.
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ABSTRACT: To examine the concepts of external validity and generalizability, and explore strategies to strengthen generalizability of research findings, because of increasing demands for knowledge utilization in an evidence-based practice environment. The concepts of external validity and generalizability are examined, considering theoretical aspects of external validity and conflicting demands for internal validity in research designs. Methodological approaches for controlling threats to external validity and strategies to enhance external validity and generalizability of findings are discussed. Generalizability of findings is not assured even if internal validity of a research study is addressed effectively through design. Strict controls to ensure internal validity can compromise generalizability. Researchers can and should use a variety of strategies to address issues of external validity and enhance generalizability of findings. Enhanced external validity and assessment of generalizability of findings can facilitate more appropriate use of research findings.Journal of Nursing Scholarship 02/2004; 36(1):16-22. DOI:10.1111/j.1547-5069.2004.04006.x · 1.64 Impact Factor
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ABSTRACT: Objectives: To determine whether a functional-task exercise program and a resistance exercise program have different effects on the ability of community-living older people to perform daily tasks.Design: A randomized, controlled, single-blind trial.Setting: Community leisure center in Utrecht, the Netherlands.Participants: Ninety-eight healthy women aged 70 and older were randomly assigned to the functional-task exercise program (function group, n=33), a resistance exercise program (resistance group, n=34), or a control group (n=31). Participants attended exercise classes three times a week for 12 weeks.Measurements: Functional task performance (Assessment of Daily Activity Performance (ADAP)), isometric knee extensor strength (IKES), handgrip strength, isometric elbow flexor strength (IEFS), and leg extension power were measured at baseline, at the end of training (at 3 months), and 6 months after the end of training (at 9 months).Results: The ADAP total score of the function group (mean change 6.8, 95% confidence interval (CI)=5.2–8.4) increased significantly more than that of the resistance group (3.2, 95% CI=1.3–5.0; P=.007) or the control group (0.3, 95% CI=−1.3–1.9; P<.001). Moreover, the ADAP total score of the resistance group did not change significantly compared with that of the control group. In contrast, IKES and IEFS increased significantly in the resistance group (12.5%, 95% CI=3.8–21.3 and 8.6%, 95% CI=3.1–14.1, respectively) compared with the function group (−2.1%, 95% CI=−5.4–1.3; P=.003 and 0.3%, 95% CI=−3.6–4.2; P=.03, respectively) and the control group (−2.7%, 95% CI=−8.6–3.2, P=.003 and 0.6%, 95% CI=−3.4–4.6; P=.04, respectively). Six months after the end of training, the increase in ADAP scores was sustained in the function group (P=.002).Conclusion: Functional-task exercises are more effective than resistance exercises at improving functional task performance in healthy elderly women and may have an important role in helping them maintain an independent lifestyle.Journal of the American Geriatrics Society 12/2004; 53(1):2 - 10. DOI:10.1111/j.1532-5415.2005.53003.x · 4.57 Impact Factor
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ABSTRACT: To evaluate the feasibility of a new functional tasks exercise program, designed to improve functional performance of community-dwelling older women, by comparing it with a resistance exercise program. A 12-week, randomized, single-blind pilot study. A community leisure center. Twenty-four community-dwelling, medically stable women (mean age, 74.6+/-4.8 y) were randomized to the functional tasks exercises (function group) or the resistance exercises (resistance group). Three participants withdrew from the study. Exercises were given 3 times weekly for 12 weeks. The functional tasks exercise program aimed to improve daily tasks in the domains first affected in older adults, whereas the resistance exercise program focused on strengthening the muscle groups that are important for functional performance. Participant satisfaction with the exercises, Assessment of Daily Activity Performance (ADAP), and, as a secondary outcome, muscle strength and power. Exercise adherence was 81% in the function group and 90% in the resistance group. Participants reported greater satisfaction with the resistance exercises than with the functional exercises. The ADAP total score improved with time (P =.001; mean change function group, 7.5 U; 95% confidence interval [CI], 2.1-12.8; resistance group, 2.8 U, 95% CI, -0.4 to 5.9), as did isometric knee extensor strength (P =.001; mean change function group, 6.4%; 95% CI, -1.6 to 14.5; resistance group, 14.4%; 95% CI, 6.4-22.2). Testing for differences in outcomes between the 2 groups showed no statistically significant differences. The functional tasks exercise program is feasible and shows promise of being more effective for functional performance than a resistance exercise program. A randomized controlled trial with a larger sample size is needed to test the difference between the 2 programs.Archives of Physical Medicine and Rehabilitation 01/2005; 85(12):1952-61. DOI:10.1016/j.apmr.2004.05.006 · 2.57 Impact Factor