According to statistics cited in the text, about what percent of cohabiting couples eventually marry:

During a repeated measures design, counseling researchers note that participants' mental health symptoms are fluctuating significantly. Which type of validity threat would most account for this occurrence?

a. History b. Instrumentation c. Attrition d. Selection

In an adoption study, resemblances are measured between the adopted child and

a. the biological parent. b. the biological parent and siblings (if any). c. the adoptive parent and siblings (if any). d. both biological parent and adoptive parent.