sensitization, or testing. problems are more likely to occur when pretest come from selfreports (e.g., through questionnaire), especially if subjects are ex he pretest. some nursing studies (e.g.,those that involve biophysiologic data), testing those that effects are a concern Instrumen Another threat related to measurements is the threat of instrumentation. This ects changes in measuring instruments or methods of measurement between two of data ection. example, if we used one measure of stress at baseline and a revised measure follow-up. any differences might reflect changes measur ing tool rather than the effect of an independent variable. Instrumentation effects can occur even if the measure used. For example,if the measuring tool yields more measuring accurate measures on the second administration (e.g.,if the people collecting the data are more experienc or less accurate measures the second time (e.g., if subjects bored or fatigued). then these differences could bias the results