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Mother and Child Health: Research Methods G.J.Ebrahim Editor Journal of Tropical Pediatrics, Oxford University Press. Preparing Case Series • All cases admitted in the time period must be included. One needs: – Precise Inclusion and exclusion criteria – What intervention was carried out for each patient, their progress and the outcome. • Influence of all variables should be accounted for. • Follow a pre-planned protocol. Give thought to how missing values, drop-outs and out-migration are to be handled. • Temporal drift is a constant danger if series need to be collected over a long time. Cross-sectional Studies • Cross-sectional studies are studies of prevalence. Proportion with an attribute or disease / Number of subjects = Prevalence. • 3 important questions to consider: – Definition of Case – Definition of the Population – Are cases and non-cases from an unbiased sample of the population? Preparing Cross-sectional Studies • In Cross-sectional studies think of: – – – – – – Sampling Procedures. Clear definition of Target Population. Clear definition of outcome. Clear definition of risk factors. Remember Confounders. Remember seasonal variations. Advantages and Disadvantages of Cross- sectional Studies Advantages • Useful for descriptive studies • Rapid, inexpensive, can provide analytic clues. • Less prone to error about exposure recall and bias Disadvantages • Unable to sort out what came first exposure or outcome • Prone to sample distortion bias. Main uses of Cross-sectional Studies • Identify and describe a problem. • Collect information for planning e.g. surveys of immunisation, antenatal care, coverage. • Evaluate utilisation rates of services. • Monitoring health status of a community by regular repeated surveys. Using Cross-sectional Studies for Hypotheses Formulation Method of Difference. If frequency of a disease is markedly different between two groups then it is likely to be caused by a particular factor that differs between them. Method of Agreement. If a factor commonly occurs in which a disease occurs with high frequency then the factor is very likely associated with the disease. Concomitant variation. Frequency of a factor varies in proportion to frequency of disease. Surveys Surveys are a form of cross-sectional studies used for: • Assessing attitudes, opinions or beliefs • To study characteristics of populations regarding behaviour e.g. health service utilisation; drug use; smoking; alcohol consumption etc. • Information about socio-demographic characteristics Modification of Cross-sectional Studies - I Trend Design Future Sampling Population Present Sampling Risk Factor Disease Prevalence Risk Factor Disease Prevalence Modification of Cross-sectional Studies - II Panel Design Present Population Risk Factor Disease Prevalence Sample Future Risk Factor Disease Prevalence Same Sample