The characteristics and design of a cohort studyA cohort study that is well-designed can provide powerful results.

The characteristics and design of a cohort studyA cohort study that is well-designed can provide powerful results. An outcome or disease-free study population is first identified by the exposure or event of interest and followed in time until the disease or outcome of interest occurs in a cohort study. Cohort studies have a temporal framework to assess causality and thus have the potential to provide the strongest scientific evidence because exposure is identified before the outcome. Because subjects are selected by their exposure status, cohort studies are particularly advantageous for examining rare exposures. Moreover, the investigator can examine many outcomes simultaneously (Song & Chung 2010).A real example of a cohort studyThe retrospective cohort study was conducted from March–June 2017 among 1043 pregnant women admitted for delivery in the Department of Obstetrics and Gynecology and obstetric characteristics, tobacco use and exposure to SHS during pregnancy were assessed by interviews. It was estimated by The World Health Organization (WHO), that tobacco use is accountable for almost six million deaths each year. One death every 6 and is projected to rise to eight million deaths per year by 2030. Adverse outcomes in pregnant women and their fetuses are shown to cause by both tobaccos which can be in smokeless or smoked forms. The harms of tobacco use in pregnancy are not limited to smoked tobacco products only. Evidence has shown that women who are pregnant and used smokeless tobacco are at a greater risk of adverse outcomes such as low birth weight, preterm labor, and stillbirth. Whereas with second-hand smoking while pregnant has been associated with the uncertain decrease in birth weight and can raise the risk of low birth weight by 22%. In this study, 1043 pregnant women between age 18 and 46 years old were admitted for delivery and more than 28 weeks of gestation was a part of this study. The proportion of women exposed to SHS during pregnancy was 69.9% among which one‐fourth of the women belonged to the family, where family members were smokers. Outcome: It was found that people who are pregnant and are exposed to second-hand smoking is said to be high in countries where more than a third of these women are exposed to second-hand smoking. Nevertheless, with the low birth of the newborns, there was no association. Second-Hand smoking exposure is high as expected because there is no strict law that prohibits smoking in public places and in homes. This study could be a preliminary step in understanding the extent of the problem, due to the lack of literature about the maternal second‐hand exposure and low birth weight in our country (Krishnamurthy, et al 2018).Cohort study described as an observational not experimental study designCohort study described as an observational study instead of experimental design because with cohort study the investigator simply observes. Researchers observe the effect of a diagnostic test, risk factor, treatment or other intervention without trying to change who is or isn’t exposed to it. In the intervention, there is no intervention that is carried out by the investigators. Case reports, cross-sectional studies, cohort studies, and case-control studies are all included in observational epidemiology which can be designed as retrospective and perspective. These are primary ways to differentiate among designs. Experimental studies on the other hand, are ones where researchers introduce an intervention and study the effects and are usually randomized, meaning the subjects are grouped by chance (Lu 2009).ReferencesSong, J. W., & Chung, C. I. (2010). Observational studies: cohort and case-control studies plastic and reconstructive surgery; 126(6): 2234–2242.Krishnamurthy, A., Chinnakali, P., Sundaram, S., Sarveswaran, G., Sivakumar, M., Krishnamoorthy, K., & Dorairajan, G. (2018). Tobacco use, exposure to second-hand smoke among pregnant women and their association with birth weight: A retrospective cohort study. Journal of Family Medicine & Primary Care, 7(4), 728–733., C. Y. (2009). Observational studies: a review of study designs, challenges, and strategies to reduce confounding. Trial design & interpretation; 63, 5, 691–697