1. A case-control study was performed to determine whether head injury was associated with an increased risk of brain tumors in children. 200 cases with brain cancer were identified from the state cancer registry and 200 controls were recruited from the same neighborhoods where the cases lived. The mothers of the children completed a questionnaire that asked them to describe their child's past history of head injury. The investigators found that the mothers of the children with brain tumors reported a past head injury for 70 of the cases while a past history of head injury was reported in 30 of the controls. What type of bias was likely to have influenced the findings of this study?

2-After investigators calculate a measure of association (RR for cohort studies and OR for case-control studies), they must evaluate whether or not the observed result is true.

3-Bias in epidemiologic studies means that the investigator is "prejudiced".

4-Control selection bias occurs in a case-control study when cases remember or report their exposures differently (more or less accurately) from controls.

The authors of a paper describe an experiment to evaluate the effect of using a cell phone on reaction time. Subjects were asked to perform a simulated driving task while talking on a cell phone. While performing this task, occasional red and green lights flashed on the computer screen. If a green light flashed, subjects were to continue driving, but if a red light flashed, subjects were to brake as quickly as possible. The reaction time (in msec) was recorded. The following summary statistics are based on a graph that appeared in the paper.

n = 49     

x = 525

     s = 70

(a)

Construct a 95% confidence interval for μ, the mean time to react to a red light while talking on a cell phone. (Round your answers to three decimal places.)

Interpret a 95% confidence interval for μ, the mean time to react to a red light while talking on a cell phone.

There is a 95% chance that the true difference in the mean time to react to a red light while talking on a cell phone is directly in the middle of these two values. There is a 95% chance that the true mean time to react to a red light while talking on a cell phone is directly in the middle of these two values.     We are 95% confident that the mean time to react to a red light while talking on a cell phone is between these two values. We are 95% confident that the true mean time to react to a green light while talking on a cell phone is directly in the middle of these two values. We are 95% confident that the true mean time to react to a green light while talking on a cell phone is between these two values.

(b)

What assumption must be made in order to generalize this confidence interval to the population of all drivers?

The assumption that the subjects of the experiment formed a random sample from the population of drivers. The assumption that the subjects of the experiment formed the population of drivers.     The assumption that the experiment captured the population of drivers. The assumption that the subjects of the experiment formed the population of distracted drivers. The assumption that the subjects of the experiment formed a random sample from the population of distracted drivers.

(c)

Suppose that the researchers wanted to estimate the mean reaction time to within 6 msec with 95% confidence. Using the sample standard deviation from the study described as a preliminary estimate of the standard deviation of reaction times, compute the required sample size. (Round your answer up to the nearest whole number.)

n =

You may need to use the appropriate table in Appendix A to answer this question.

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