EPID6430 Advanced Epidemiology Essay.

Participants in the research were exposed to leisure-time exercise that included brisk walking for 36 minutes where the risk for CHD was less as compared to non-exercisers. The risk for the CHD is high among the non-workers and sedentary lifestyle as compared to people who participated in some form of physical exercise.

In the given paper, the outcome of the exposure was that the leisure-time exercise, including the brisk walking for 35-40 minutes was a protective factor for the coronary heart disease (CHD) and the sedentary lifestyle acted as a strong factor for CHD. This intervention was important as there is limited information about the CHD care in India and the importance of physical exercise that would reduce the risk of CHD in India. It also requires promotion of physical exercise among the people in India. Out of the controls, 48% participants were engaged in highest level physical exercise compared to as 38% of the total cases. The participants engaged in physical exercise and brisk walking had a relative risk for CHD of 0.45 as compared to the non-exercisers. The participants who are engaged in sedentary lifestyle had a CHD risk of 1.88 as compared to the leisure-time exercisers.

Rastogi et al., (2004) used hospital-based case-control study to assess the association between the risk for CHD and leisure-time exercise and non-work sedentary lifestyle.

The chosen study population for the research was chosen from the hospital where 350 cases were taken of acute myocardial infarction and around 700 controls were taken that matched the gender, age and hospital in Bangalore and New Delhi.

The main findings were out of the controls, 48% of the participants were involved in leisure-time exercise as compared to 38% of the total cases. After the sex and age adjusted analyses, the leisure-time exercise that is equivalent to brisk waling of 36 minutes per day showed a less relative risk of .045 (95% CI: 0.31, 0.66) as compared to the noon-exercisers. The findings also showed that there is a positive association between the CHD risk and non-work sedentary activities. People who were engaged in more than 3.6 hours of sedentary activities like television watching had an 1.88 elevated risk (95% CI: 1.09, 3.20) as compared to the less than 70 minutes per day.

This case control study has been a clinical experiment to judge the impact that regular physical activity can bring to the risk factor level of coronary heart diseases in the potentially susceptible population. In the particular study, 350 subjects were chosen for the trial and were compared to 700 control subjects. Hence, in the study design each subject was compared to two consecutive controls chosen of within 5 years of age as compared to the subject. The results indicated at the reduction of incidence risk factor to coronary heart diseases as compared to those who were not engaged in physical exercise. Now the relationship between the exposure and the outcome is not dependent on the future implications hence it cannot be deemed to be having a non casual relationship between exposure and outcome. However there are some confounding factors that might or might not have affected the outcome and its intensity.

Measurement bias is a part of any qualitative study design, and as the case study selected for this assignment has incorporated qualitative design, the chances of measurement bias are not completely eradicated. In this case the leisure time for the subjects were determined across different levels and when a variable is judged across different levels or dimensions there is a significant chances of measurement bias, and it can have the potential to affect the outcome of the study (Rastogi et al., 2014).

Confounders are the associated factors to exposure in a epidemiological study that has the significant potential to alter or affect the outcome of the study. In the research study chosen for this assignment, the exposure for the subject population was a regular physical activity regime that equals to 36 minutes of brisk walking and how it can affect or reduce the risk factors to coronary heart diseases significantly. However, other confounding factors that are associated with the lifestyle choices of the chosen subject population, like smoking, drinking, dietary habits which are equally important and substantial factors in the susceptibility to coronary heart diseases, are standardized in the data analysis procedure. Hence the chances of these major confounding factors cannot be accused of imparting bias to the outcome. The factors that might have had negative effect on the outcome of the study and were not taken into consideration, the selection based bias in the scenario. Hospital based selection in place for population based selection can have a biased view of the incidence of coronary heart diseases as compared to the research setting based on the entire population. 

Chance variation is defined as the significant difference in between the expected and derived outcome of any statistical analysis. In this particular study, the hypothesis for this study was that regular leisure time physical activity can reduce the risk for coronary heart diseases in the susceptible subjects as compared to sedentary lifestyle choices. The results were successful in proving what was initially hypothesized in the research study hence there is no significant chance variation in the study (Rastogi et al., 2014).

A temporal relationship in a statistical study is concerned with time being a factor affecting the relationship between exposure and outcome in statistical analysis. Now in this research study, the exposure was leisure time physical activity and the outcome has been the reduced risk for coronary heart disease in the subjects. Now the subject population selected was already dealing with a history of myocardial infarction there cannot be a temporal relationship between the exposure and the outcome (Rastogi et al., 2014).

However, there surely is a strong relationship between the exposure and the outcome. As mentioned above in the assignment, the exposure to leisure time physical activity has resulted into the reduction of risk factors to coronary heart diseases. Now in the study 48% of the cases were involved in leisure time activity and were compared to 38% of the case subjects. The risk factor for the subjects that were on leisure time exercise had 0.45 units where as the non exercising subject group had the risk factor incidence of 1.88. Now the vast difference between the outcome for the control and case subject groups are clearly indicative of the strong impact of the exposure that has resulted into this particular outcome (Rastogi et al., 2014).

Dose response relationship can be defined as the relationship between different levels of exposure and its effect on the outcome of the study. It has to be understood that in an exploratory study involving human subjects there are a number of external and internal factors that are associated with the outcome generated. To ensure that bias due to confounding factors is minimal, the research study under consideration for this particular assignment, the leisure time exposure and its effect on reduction of risk factors to coronary heart diseases were judged across different levels. Usage of this differential dosage is clearly indicative of the dose response relationship in between the exposure and outcome (Rastogi et al., 2014).

From the results and discussion of the study, it can be concluded that the study was consistent with the differential exposure and its effects. On a more elaborative note, with the subject population with zero leisure time activity showed no reduction in the risk factors. On the other hand as the exposure to physical activity increased the risk to CHD showed signs of reduction. Therefore it can safely be concluded that there is a consistent inverse relationship between the exposure and outcome in this research study (Rastogi et al., 2014).

A research study cannot be valid with without being relatable and comparable to other significant and similar study designs. In this case the main idea behind the research study chosen is the affect of physical exercise albeit as a leisure time activity has a profound effect on reducing the risk factor to coronary heart diseases in the susceptible population. Coronary heart disorders are one of the main public health concerns in this current scenario, and hence preventative measures like exercise regime have been and continues to be fertile ground for exploratory research studies.

The research article by Lee and his coauthors is a similar study to the one under discussion in this assignment. In this article the researchers have very clearly demonstrated the positive effects of leisure time running on the mortality due to coronary heart diseases, very similar results as compared to the study done here. However, in the article by Lee the leisure time running activity indicated at 5 to 10 minutes of running at 6 mile per hour speed was effective in reducing the mortality rates whereas the study design for this research study is much more diverse (Lee et al., 2014).

Another research study on effectiveness of physical activity on decreasing the risk factor to coronary heart diseases by Gielen and his coauthors have also indicated at how effectively physical exercise can improve the metabolic functions of the body and can reduce the risks to a heart attack (Gielen et al., 2015). However, this particular study has very critically explained the data on a molecular level rather than an exposure- outcome relationship based research, the findings of this study also aligns exceptionally well with the research study under consideration for this particular assignment. 

As the research study has been done on human case and control subjects, this result is absolutely plausible in term of a biological mechanism.

The findings of this study is externally valid for the susceptible population to coronary heart complications but is not completely generalizable as the subject population selected were with a prior incidence of a myocardial infarction. The study can be executed with the source population on the condition of the population having a prior medical history of heart disorders or having had a previous history of myocardial infarction, although the findings might not correlate if the target population and setting is changed (Rastogi et al., 2014). 

The study results cannot be applied to other study populations unless the population selected as the case subjects have had a prior history of myocardial complications, otherwise it will change the research setting completely and can alter the results generated completely. It has to be considered that the confounding factors has been standardized with respect to the subject population setting chosen, altering the population choice without considering the confounders can also alter the outcome generated (Rastogi et al., 2014).

Gielen, S., Laughlin, M. H., O’Conner, C., & Duncker, D. J. (2015). Exercise training in patients with heart disease: review of beneficial effects and clinical recommendations. Progress in cardiovascular diseases, 57(4), 347-355.

Lee, D. C., Pate, R. R., Lavie, C. J., Sui, X., Church, T. S., & Blair, S. N. (2014). Leisure-time running reduces all-cause and cardiovascular mortality risk. Journal of the American College of Cardiology, 64(5), 472-481.

Rastogi, T., Vaz, M., Spiegelman, D., Reddy, K. S., Bharathi, A. V., Stampfer, M. J., ... & Ascherio, A. (2004). Physical activity and risk of coronary heart disease in India. International journal of epidemiology, 33(4), 759-767.