The estimated prevalence of post-traumatic stress disorder among rape victims is:

You want to conduct a study involving the use of technology by 20, 40, 60, and 80 -year olds

However, a colleague tells you that your study will fail because your participants will naturally vary on important variables such as education. Your colleague adds that matching your participants on demographic variables will solve one problem, but create another. That is, your age groups are equated on these variables, but in doing so, you have compromised external validity.  Describe how you would respond to your colleague's critique. What will be an ideal response?

What percentage of adults over age 65 years in developed countries report symptoms of arthritis?

a. 70% b. 50% c. 30% d. 10%