Final answer:
External validity threats that affect confidence in generalizability include selection bias, history, testing effects, and maturation. These can be addressed through methods like random sampling and controlling for time-related changes.
Step-by-step explanation:
The threats to external validity that can compromise confidence in stating whether a study's results are generalizable include selection bias, history, testing effects, and maturation:
- Selection Bias: Occurs when the participants chosen for a study do not accurately represent the larger population.
- History: Refers to specific events that occur between the first and second measurement that can influence the study's outcomes.
- Testing Effects: The mere act of testing may change participants' behavior or responses in subsequent testings.
- Maturation: Participants may naturally change or grow over time, independently of the study, affecting the results.
It's important for researchers to account for these factors. For instance, selection bias can be reduced by using random sampling techniques, whereas maturation effects can be controlled by adopting shorter study periods or using age-matched comparison groups.