Title 8. COHORT STUDIES.pdf ✅

PHARMD GURU Page 1 INTRODUCTION: 1) Methodologically cohort study is diametrically opposite of case control study. 2) A cohort is a nothing but a group. Hence a cohort study is a study of groups of patients having some common drug exposure of interest. EXAMPLES OF COHORT INCLUDE:  Pharm.D students of particular college of pharmacy.  Patients coming to a particular hospital.  People with a particular genetic trait or adults admitted in a specialty hospital. 3) In a cohort study, a group of individuals exposed to a putative risk factor and a group who arc unexposed to the risk factor are followed over time (often years) to determine the occurrence of disease. 4) The incidence of disease in the exposed group is compared with the incidence of disease in the unexposed group. 5) The relative risk (incidence risk or incidence rate) is used to assess whether the exposure and disease are causally linked. COHORT STUDIES CAN BE PROSPECTIVE OR RETROSPECTIVE IN NATURE: PROSPECTIVE COHORT STUDY:  A prospective cohort study is also called a concurrent cohort study, where the subjects have been followed up for a period and the outcomes of interest are recorded.  It is considered as the best type of cohort study as far as scientific evidence and control over the factors of interest are considered. It looks forward in time and allows the researcher maximum control over the study definition and its conduct. The potential confounding factors and variables that must be controlled in the study process can be defined and measured in prospective cohort studies. It is very expensive. COHORT STUDIES


PHARMD GURU Page 4 study where disease rates among individuals from a particular occupational group are compared with an external standard population, bias may be introduced if membership of the exposed cohort is partly dependent upon health (which may be related to the presence or absence of the health outcome under investigation).  Individuals, who are employed, for example, are generally healthy by nature of their ability to work Therefore, mortality or morbidity rates in the occupation group cohort may be initially lower than in the population as a whole, which includes individuals who are too ill to work  In order to minimize the potential for this form of bias, a comparison group may be selected from a group of workers with different jobs performed at different locations within a single facility. For example, a group of non-exposed office workers. Alternatively, the comparison group may he selected from an external population of employed individuals. ANALYSIS OF COHORT STUDIES:  Analysis of a cohort study uses either the risk or the rate ratio of disease in the exposed cohort compared with the rate or risk in the unexposed cohort.  Note that the risk ratio uses as a denominator the entire group recruited at the start of the study, while the rate ratio uses as a denominator the person years, which takes account of losses to follow-up. EXAMPLE: Calculation of the rate ratio from a hypothetical cohort study of smoking and cancer of the pancreas followed for 1 year. Pancreatic cancer No disease Total Incidence rate Smokers 42 27,000 27,042 1.5/1000/yr Non-smokers 07 63,000 63,007 0.1/1000/yr Total 49 90,000 90,049 From the above table, taken from a hypothetical cohort study to investigate the association between smoking and cancer of the pancreas, the relative and attributable risk can be calculated as follows: RATE RATIO = Incidence rate in exposed group incidence rate in unexposed group