we identified five time-related factors that can threaten the
internal validity of a within-subjects experimental design. Briefly
reviewing, they are:
• History. Scores may be affected by changing events outside the study.
• Maturation. Scores may be affected by physiological or psychological
changes in the participants.
• Instrumentation. Scores may by affected by changes in the measuring
instrument.
• Testing effects. Scores may be affected by experience in prior
treatment conditions.
• Statistical Regression. Extreme scores may become less extreme as a
result of statistical regression.