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

Population

Disease Prevalence

Risk Factor

Present

Sampling

Future

Risk Factor

Disease Prevalence

Sampling

Modification of Cross-sectional Studies - II

Panel Design

PopulationRisk

Factor

Disease Prevalence

Risk Factor

Disease Prevalence

Sample Same Sample

Present Future