1-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. Which of the following is the correct interpretation of the p-value?

a-Children who received the new vaccine had a 50% reduced risk (or half the risk) of developing pertussis compared to those who received the old vaccine.

b-Given that the null hypothesis is true, there is a 1% probability of observing these or more extreme results.

c-I have 95% confidence that the true relative risk lies in the interval from 0.2 to 0.8.

d- The number of excess cases of pertussis among those who received the old vaccine is 10 per 1000.

2- The null hypothesis (Ho):

a-Assumes there is an association between exposure and outcome

b-Assumes there is no association between exposure and outcome

c-Assumes there is no bias or confounding

d-Assumes that the results observed are of medical or public health significance

3-Which of the following sets of measures of association represent the values of the null hypotheses? Note that RD is risk difference, RR is risk ratio, and OR is odds ratio.

a-RD?0, RR?0, OR?0

b-RD=2.0, RR=6.0, OR=6.7

c-RD=0, RR=1, OR=1

d-None of the above

4-Which of the following sets of measures of association represent the values of the alternative hypothesis (HA)? Note that RD is risk difference, RR is risk ratio, and OR is odds ratio.

a-RD=0, RR=1, OR=2

b-RD=2.0, RR=6.0, OR=6.7

c-RD=0, RR=1, OR=1

d-None of the above