epidemiologic study designs-1.pdf

Epidemiological Study Designs  Learning Objectives: Define Epidemiology and its aim. Identify the uses of descriptive epidemiology. Types of study design. focus on descriptive study design (cross- sectional).  Definition of Epidemiology The study of the distribution and...

Epidemiological Study Designs  Learning Objectives: Define Epidemiology and its aim. Identify the uses of descriptive epidemiology. Types of study design. focus on descriptive study design (cross- sectional).  Definition of Epidemiology The study of the distribution and determinants of health related states and events in populations and the application of this study to control of health problems Aims of epidemiology 1. To describe the distribution and magnitude of health and disease problems in population. 2. To identify etiological factors in the pathogenesis of disease. 3. To provide the data essential to the planning, implementation and evaluation of health services and to set up priorities between services  Descriptive epidemiology: Describes the distribution of health-related events by Person – age, race, gender, marital status, socioeconomic status, occupation and behaviors Time – Changing or stable?, Seasonal or cyclic variation Place – Geographically restricted or widespread – Disease mapping The Basic Triad of Descriptive Epidemiology Time Place Person  Descriptive epidemiology: Prevalence is the number of existing cases of disease in the population during a defined period. – Prevalence is a measure of burden of disease or health problem in a population Incidence is the number of new cases of disease that develop in the population during a defined period. – Incidence rate is a measure of the probability of the event among persons at risk.  Study design Study design is a specific plan or protocol for conducting the study, which allows the investigator to translate the conceptual hypothesis into an operational one.  Types of Studies Observational–no manipulation of study factor by the investigator (natural observation) Experimental -study factor/s (exposure) is manipulated by the investigator to test Descriptive studies Describe occurrence of outcome. Analytical studies Describe association between exposure and outcome Experimental studies Compare treatment modalities  How could we select the best Study design ? Purpose of the study State of existing knowledge (in relation to study question) Characteristics of the study variables Latency Feasibility  Purpose of the study Study of prevalance: cross sectional study. Study of etiology: -Case-control -Cohort Study of therapy: – Lab experiments – Clinical trials – Community intervention  State of existing knowledge (in relation to study question) New idea: – Cross-sectional New hypothesis: – Cross-sectional – Case-control Newly claimed association: – Case-control: replication, confirmation – Cohort: stronger evidence towards causation Confirmed association: – Experiment/intervention: to prove causation  A case report is a detailed report of the diagnosis, treatment, response to treatment, and follow-up after treatment of an individual patient. A case series is group of case reports involving patients who were given similar treatment.  A cross-sectional studies – Type of observational study – The research has no control over the exposure of interest. It involves – Identifying a defined population at a particular point in time – Measuring a range of variables on an individual basis – Exposure status and disease status are measured at one point in time or over a period.  Design of cross-sectional study The problem to be studied must be clearly described and a thorough literature review. Specific objectives need to be formulated. Sampling is an important issue to ensure that the objectives can be met in the most efficient way. The information has to be collected and data collection techniques need to be decided. (Exposure and outcome are measured at the same time)  Fieldwork needs planning: – Who is available to collect the data ? – Do they need training ? – If more than one is to collect the data then it is necessary to assess between-observer variation. The collection, coding and entry of data need planning. A pilot study is essential to test the proposed methods and make any alternations as necessary.  Analysis of cross-sectional study Standard descriptive statistics: mean, median, quartiles, and mode measure of dispersion or variability: standard deviation; measure precision: standard error, and confidence intervals.  Uses of cross-sectional studies (Describtive studies) Prevalence: The studies are commonly used to describe the burden of disease in the community and its distribution. Describe the frequency, natural history and possible determainants of the disease. Describe the characteristics: of the disease and those affected.  KAP (knowledges, attitudes, and practices ) study: – KAP studies help to build up a better understanding of the behavior of the population, without necessarily relating this to any disease or health outcome. Management tool: health service managers and planners may make use of cross-sectional survey to assess utilization and effectiveness of service. Development of hypothesis: Hypotheses on the causes of disease may be developed using data from cross-sectional study survey.  Advantages Conducted short period of time(easy, quick). Relatively inexpensive Study the distribution of the disease and help in identifying priorities. suggest risk factors or (protective factors) for a disease.  Disadvantages (limitations) Not a useful study type to establish causal relationships, because measurement of exposure and disease is conducted at the same time. The prevalance not the incidence is the focus of the study. Not suitable for studying rare disease, highly fatal diseases or a disease with short duration of expression