A study followed patients for four years after they had a heart attack (K. Mukamal et al., Circulation, vol. 105, 2002, pp. 2476–2481). Patients were interviewed about their weekly caffeinated tea consumption during the year before the heart attack. The relative risk of another heart attack during the study period for those who reported drinking at least 14 cups a week, compared to those who reported not drinking tea, was 0.56, with a 95% confidence interval of 0.37 to 0.84.
a. Interpret the confidence interval for the population relative risk.
b. According to these results, can we conclude that in a corresponding population, tea drinking reduces the chance of another heart attack? Explain.