Glossary terms for 'W'
|Washout period||In a crossover study (see above), the period of time between the first and second treatment designed to allow the effects of the intervention to wear off and the outcome measure to return to baseline. For example, in a cross-over trial comparing a diuretic medication to placebo for treatment of high blood pressure, the investigator might allow a month with no treatment between the two treatment periods to allow blood pressure return to baseline.|
|Within-group design||A study design in which measurements are compared in a single group of participants, most often at two different time periods. This design eliminates confounding because each participant serves as his own control. However, within-group designs are susceptible to learning effects, regression to the mean, and secular trends. For example, fasting blood glucose levels might be measured among a group of patients with diabetes before starting an exercise program and after the program has been completed to determine if exercise lowers fasting glucose levels. See also time-series design, between-groups design and one sample t-test.|
Glossary material from Hulley SB et al. Designing Clinical Research, 4th ed. Philadelphia, Lippincott Williams & Wilkins, 2013.