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: Given that retention rates for weight-loss trials have not significantly improved in the past 20 years, identifying effective techniques to enhance retention is critical. This paper describes a conceptual and practical advance that may have improved retention in a behavioral weight-loss trial-the novel application of motivational interviewing techniques to diffuse ambivalence during interactive group-based orientation sessions prior to randomization. These orientation sessions addressed ambivalence about making eating and exercise behavior changes, ambivalence about joining a randomized controlled trial, and unrealistic weight-loss expectations. During these sessions, overweight and obese men and women learned about the health benefits of modest weight loss as well as trial design, the importance of a control condition, random assignment and the impact of dropouts. Participants were then divided into groups of three or four, and asked to generate two pros and two cons of being assigned to a control condition and an active condition. Participants shared their pros and cons with the larger group, while the investigator asked open-ended questions, engaged in reflective listening and avoided taking a 'pro-change' position. Retention was high, with 96% of the participants (N = 162) completing 18-month clinic visits.Health Education Research 09/2005; 20(4):439-47. · 1.66 Impact Factor
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ABSTRACT: Ageing is characterised by a reduction in physical reserve, the physiological capacity in excess of that needed for daily activities, that provides a margin of safety that absorbs age- or disease-related changes without a loss in function. When physical capacity falls below the ability required for the performance of daily tasks, functional limitations and a loss of independence may occur. Approximately 20% of people between 65 and 75 years of age report problems with activities of daily living (ADLs), a proportion which increases to 48% in people older than 85. Exercise studies and exercise promotion for older adults offer the potential for improving the performance of daily activities and quality of life. However, the results of current exercise programmes are limited and inconsistent. The University Medical Center (UMC) Utrecht developed an exercise programme focusing on functional tasks of everyday life, tasks that are affected early in the ageing process. The aim of the studies described in this thesis was to study the difference in effect between functional tasks exercises and resistance strength exercises on the physical functional performance and health-related quality of life of older community-dwelling women. A pilot study with 24 community-dwelling, medically stable women (mean age 74.6 ?4.8) demonstrated that both exercise programmes were feasible and well tolerated by women over the age of 70 years and living in the community. Ninety-eight healthy women aged 70 and older were randomly assigned to either the function group (n = 33), the resistance group (n = 34) or a control group (n = 31). Participants attended exercise classes three times a week for 12 weeks. Functional task performance (ADAP test), 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). The ADAP assessment of daily activity performance (ADAP) test includes 16 common tasks, such as transferring laundry and boarding a bus, performed at maximal effort. proved to be reliable and valid for measuring the performance of daily activities by community-dwelling older women. The ADAP total score increased more in the function group than in the resistance group or the control group. The ADAP total score of the resistance group did not change compared with the control group. In contrast, IKES and IEFS increased significantly in the resistance group compared with the function group and the control group. Six months after the end of training, the increase in ADAP scores were sustained in the function group, whereas the strength gains of the resistance group had disappeared. Physical activity scores demonstrated that functional tasks exercises may positively influence daily habits more than resistance training, which means that older individuals may continue exercising and thus maintain the effects of exercise. Functional tasks exercises are more effective in improving physical functional performance than common resistance strength exercises and the effects are preserved for longer than the gain in muscle strength achieved with resistance exercises.01/2006;
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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. · 4.22 Impact Factor