Epidemiological Designs Dr. MUSTAQUE AHMED MBBS,MD(COMM MEDICINE),FELLOWSHIP

Class objectives 1. Overview of study designs 2. Classify epidemiological study designs

Epidemiological approach By Kipling What, When , Where Why, Who, how 1- what is the event and what is its magnitude(problem) 2-when did it happen (time distribution) 3-where did it happen (place distribution) 4- who are affected (person distribution) 5- why did it happen (cause of disease) 6- How did it happen (cause of disease)

Epidemiological design TYPES OF EPIDEMIOLOGICAL STUDY UNIT OF STUDY OBSERVATION STUDY A-DESCRIPTIVE STUDIES( HYPOTHESIS FORMULATION) B- ANALYTICAL STUDIES(HYPOTHESIS TESTING)- CAUSES 1-CROSS-SECTIONAL individual 2-CASE CONTROL 3-COHORT 4-ECOLOGICAL population EXPERIMENTAL STUDIES ( HYPOTHESIS CONFIRMATION) 1-RANDOMIZED CONTROLLED TRIAL Patients 2-FIELD TRIAL Healthy people 3-COMMUNITY TRIAL Community 4-CLINICAL TRIAL patients

Overview In epidemiology, measuring the occurrence of disease or other health- related events in a population is only a beginning. Epidemiologists are also interested in assessing whether an exposure/risk factors is associated with a particular disease (or other outcome of interest).

For instance, researchers may be Interested in Obtaining answers to the following questions Does a high-fat diet increase the risk of breast cancer? High-fat diet Breast cancer (exposure) (outcome) Does hepatitis B virus infection increase the risk of liver cancer? Hepatitis B infection Liver cancer (exposure) (outcome) The first Step in an epidemiological study is to define the hypothesis to be tested. This should include a precise definition of the exposure(s) and outcome(s) under study. There are two basic approaches to assessing whether an exposure is associated with a particular outcome: Experimental and Observational

OBSERVATIONAL Observational studies Allow nature to take its cause; the investigator measures but does not intervene Descriptive study: focuses on the distribution of disease.. Analytical study analysis underlying causes of the disease (determinants of disease) .

CROSS- SECTIONAL STUDY-A cross-sectional study is a type of  observational study that involves the analysis of data collected from a population, or a representative subset, at one specific point in time and results is projected on the whole population. COHORT STUDY-This is a type of analytic design - in which a group or groups of individuals are defined on the basis of presence or absence of exposure to a suspected risk factor for a disease. In this Study design it involves follow up . CASE CONTROL STUDY- the study is designed to establish the cause of disease(hypothesis testing) by investigating the associations between exposure to a risk factor and occurrence of disease.

ANALYTICAL STUDIES Two basic designs: Case – control or retrospective study Cohort or prospective NOTE There must be a comparison group No control No conclusion(NCNC)

CASE CONTROL STUDY A group of affected people is compared to unaffected people(the control) Subjects are selected based on a particular outcome and a study goes backwards in time to try to detect the causes or risk factors that may have earlier been reported in a descriptive study Subject selected on the basis of disease[e.g lung cancer]. Sometimes called a retrospective study because of the direction of study

CASE CONTROL STUDY

COHORT STUDY A cohort is a group of people who have something in common and remain part of a group over an extended time A group of people exposed to a suspected etiological agent are compared with a matched control who have not been similarly exposed. [aetiological factor; cigarette smoking] Follow-up over a period to compare the outcome

EXPERIMENTAL STUDIES Experimental or interventional studies: involve an active attempt to change a disease determinant(e.g an exposure or a behaviour) or the progress of a disaese (through treatment) The studies are based on a group which has had the experience compared with control group which has not had the experience.

2. Experimental studies/ Intervention studies Randomized controlled trials –patients as unit of study clinical trials with patients as unit of study. Testing a new drug or regime on the person with specific disease Field trials studies with Healthy people as unit of study Community trials, communities as unit of study

Clinical trial Randomized control trial

Community trials Community trial Field trial

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