Prepostmetingen

Prepostmetingen, also known as pretest–posttest measurements, refer to a simple longitudinal research design in which the same individuals are measured on a variable before and after an intervention. The aim is to estimate the change attributable to the intervention. Common variants include pretest-posttest designs with a control group and within-subject designs without a control group. In the with-control design, participants are randomly assigned or matched to receive the intervention or not, while in the without-control design all participants are measured before and after.

Data collection centers on reliable and valid instruments. The analysis often uses change scores (post minus pre) or statistical models that account for baseline values, such as ANCOVA with pretest as covariate, repeated measures ANOVA, or mixed-effects models.

Advantages: intuitive, straightforward to implement, suitable for evaluating programs and policies when randomization is not possible. Limitations: threat to internal validity if there is no control group, such as maturation, history, regression to the mean, and testing effects. Without a control group it is difficult to attribute observed change solely to the intervention. Additional issues include measurement error and drop-out.

Ethical considerations include informed consent and data privacy. Timing and consistency of measurements are important to reduce bias, for example using the same instruments and conditions for pre and post measurements.

Overall, prepostmetingen are a common tool in education, health, and social sciences to assess the impact of interventions, but they are strongest when combined with a control group or rigorous statistical controls to mitigate confounding factors.