Transcript Preparing case Series

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:
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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