In a study of the relationship between exercise and heart attacks among women who do not smoke, gender plays a role as a confounder. This is because men and women engage in different levels and types of exercise (Saracci, 2010). Engaging in exercise lowers the occurrence of heart diseases. Gender is a confounder because men engage in exercise more often than women. Thus, men have a leaner mass with more muscles than fat compared to women. , women are more predisposed to heart attacks if exercise is not considered (Szklo & Nieto, 2007).
Smoking is a confounding factor in a study of alcohol consumption and liver cirrhosis. Smoking has a negative effect to the liver in both alcoholics and non-alcoholics (Webb & Bain, 2011). The intensity of liver cirrhosis is intensified if the individual is a smoker. This is because chemicals released during smoking lead to oxidative stress and lipid peroxidation. If the period of exposure is prolonged, fibrosis develops. In case of non-alcoholics, smoking produces pro-inflammatory cytokines which cause damage of the liver cells (Rothman et al, 2008).
An odds ratio of 1.2 implies that the occurrence of obesity is likely to occur 1.2 times with low socioeconomic status. The range (0.8-1.5) of the 95% confidence interval shows that the level of precision was high (Stewart, 2010) because the interval is small (0.7). A large sample was used to conduct this study which is shown by the small confidence interval (Brownson & Petitti, 2006).
A positive association was observed between the consumption of red meat and the occurrence of colon cancer (Woodward, 2005). This is because the relative risk (3) is greater than one. A p-value of 0.15 is small and indicates that the observed association is big since a large study was conducted (Woodward, 2005).
In a study of the relationship between cigarette smoking and lung cancer, occurrence of lung cancer is seven times more likely to occur in smokers than non-smokers. The range (3.0-11.4) shows a very big difference which indicates that the level of precision in the results is low. This is due to a low sample size (Webb & Bain, 2011).
The crude odd ratios of cigarette smoking and lung cancer are calculated as follows:
Crude odd ratio = (450*225)/ (250*200) = 2.0
This means that the occurrence of lung cancer is two times more likely to occur in cigarette smokers.
The table above shows the association of alcohol use with occurrence of coronary heart disease (CHD). This ratio shows that coronary heart disease is two times more likely to occur in people who drink alcohol.
Odds Ratio = (90*90)/ (60*60) = 2.25
Odd Ratio in smokers = (80*10)/ (20*40) = 1.0
Odd Ratio in non smokers = (10*80)/ (40*20) = 1.0
Smoking was found to be a confounder of the association because occurrence of coronary heart disease was higher in smokers than in non-smokers. After controlling smoking, the number of cases was lower in people who did not take alcohol. In a study of the association between taking a driver’s education class and the risk of being in an accident, the relative risk was calculated as follows:
Relative risk = [(70/70+170)]/ [(80/80+130)] = 0.40
This value shows that there is a negative association and this shows a decreased risk of occurrence with a driver’s education. The following calculations were done when gender was proposed to be an effect modifier (Rao, 2008).
Relative Risk in women = [(10/10+50)]/ [(40/40+80)] = 0.4
Relative Risk in men = [(60/60+120)]/ [(40/40+80)] = 1.0
The relative risk of being in an accident is higher in men than in men. 0.4 shows a decreased risk of accidents and the value 1.0 shows an increased risk.
References
Brownson, R. C., & Petitti, D. B. (2006). Applied epidemiology: Theory to practice. Oxford; New York: Oxford University Press.
Rao, C. R. (2008). Epidemiology and medical statistics. Amsterdam [u.a.: Elsevier.
Rothman, K. J., Greenland, S., & Lash, T. L. (2008). Modern epidemiology. Philadelphia: Lippincott Williams & Wilkins.
Saracci, R. (2010). Epidemiology: A very short introduction. Oxford: Oxford University Press.
Stewart, A. (2010). Basic statistics and epidemiology: A practical guide. Oxford [etc.: Radcliffe Publishing.
Szklo, M., & Nieto, F. J. (2007). Epidemiology: Beyond the basics. Sudbury, Mass.; Toronto: Jones and Bartlett Publishers.
Webb, P., & Bain, C. (2011). Essential epidemiology: An introduction for students and health professionals. Cambridge [u.a.: Cambridge Univ. Press.
Woodward, M. (2005). Epidemiology: Study design and data analysis. Boca Raton [u.a.: Chapman & Hall/CRC.