External Threats to Validity

This chapter discusses strategies researchers use to address threats to the external validity (i.e. generalizability) of research results. It describes threats to external validity in terms of populations, times, and situations. Within these factors, it considers specific threats to external validity, such as: (1) interactions among different treatments or conditions; (2) interactions between treatments and methods of data collection; (3) interactions of treatments with selection; (4) interactions of situation with treatment; and (5) interactions of history with treatment. Each of these factors can limit the generalizability of research results and, therefore, the validity of claims based on those results.