Select the correct statement concerning the selection of con

Select the correct statement concerning the selection of controls in a case control study:

Randomization is often employed to help assure comparability of cases and controls.

Controls should come from a different geographic area than the cases.

Matching can be used to reduce confounding bias

It is best to identify controls with conditions that are related to the outcome in the case control study.

A study found that people in a city were more likely to visit the emergency room on days with high ozone concentrations. The effect was small but statistically significant. The study collected information on demographics and risk factors and found that people with asthma had a ten-fold greater likelihood of being admitted to the emergency room on days with high ozone. Which of the following is true:

Asthma appears to be an effect modifier.

Asthma appears to be a confounding factor.

People with asthma must be removed from the study to reduce bias.

The results are most likely due to random error

In a cohort of 3,000 employees working full-time as cashiers at the Piggly Wiggly, there were 760 ergonomic injuries to wrists during a 2-year time period. Among 5,000 people who are not employees of the Piggly Wiggly, there were 210 wrist injuries during the same time period. Calculate the relative risk of ergonomic injuries for cashiers compared to non-cashiers. Present to 1 decimal point.

Solution

Randomization is often employed to help assure comparability of cases and controls.

The results are most likely due to random error

relative risk of ergonomic injuries for cashiers

760 / 3000 = 0.2533

relative risk of ergonomic injuries for non-cashiers

210/5000 =0.042