A randomized experimental study was conducted to evaluate the effectiveness of a

Question

A randomized experimental study was conducted to evaluate the effectiveness of a new pertussis vaccine. One-thousand healthy children were randomized to receive either the new vaccine (500 children) or the old vaccine (500 children). The children were followed for two years to monitor the incidence of pertussis. At the end of the study, the risk ratio for developing pertussis was 0.5 among the children who received the new vaccine compared to children who received the old vaccine. The 95% confidence interval for this relative risk was 0.2-0.8 and the p value was 0.01.

Suppose that the same experimental study were conducted and that the same risk ratio were observed (RR=0.5) using a much larger population --1,000 children in each group instead of 500 in each group.

Would the 95% confidence interval be narrower or wider in the study with 2,000 children as compared to the study with 1,000 children?

Which one:                   Narrower                      Wider

Would the numeric value of the p value be smaller or larger in the study with 2,000 children as compared to the study with 1,000 children?

Which one:                   Smaller                        Larger

Explanation / Answer

as sample size increase margin of error decreases hence width of confidence interval decreases if we increase sample size

hence

he 95% confidence interval be narrower in the study with 2,000 children as compared to the study with 1,000 children

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