Mr. dotson wants to know if the neighbors on his street would be interested in a community watch. he surveys every fourth household on the street and concluded that 70% would be interested. a. not valid, because he should have surveyed people in the entire city. b. there is no way to determine if the conclusion is valid or invalid. c. valid, it is an unbiased systematic random sample. d. not valid, because he needs to survey every person for it to be accurate.

Aresearch study is studying the effects of a new drug for osteoporosis alzheimer's disease (ad) for women above the age of 65 years. a group of individuals with osteoporosis is randomized into two groups. one group is treated conventionally, and the second group is treated with the new medication. assessments are made at 3, 6, 12, 36, and 48 months. the conventionally treated group is assessed for ad using a serum blood test, and the treatment group is assessed for ad using a pet radiotracer that binds to beta-amyloid plaques. in comparing these 2 trial arms, the authors of the study may encounter which type of bias? a. selection bias on the risk of developing b. measurement bias c. confounding bias d. recall bias e. lead-time bias