L5 Cross sectional studies Flashcards
Define a cross sectional study.
A type of observational study that involves the analysis of data collected from a population at one specific point in time or over a short time period (e.g. calendar year).
Define descriptive epidemiology.
When no analytical work is carried out (therefore no comparisons of rates, associations between risk factors etc.)
How is a cross sectional study limited?
Because they are only carried out at one point in time and therefore give no indication of sequence of events.
What is the purpose of cross sectional studies?
To determine prevalence of specified outcome for population or subgroups at a particular point in time.
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Sample Selection & Response Rates
Sample frame - Used to select sample Sample frame
Response rate - Determine how well results can be generalised to whole population
Sample used - Often taken from whole population
Optimum - If sample selected used random method likely to be very representative
For results to represent the population:
- Selected sample must be representative
- Also – Responders need to be representative
- Nonresponse – Common problem in large surveys
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List techniques to minimize non-response. (4)
- Telephone & mail prompting
- Second & third mailing of surveys
- Letters stressing importance of replying
- Incentives
Define the advantages of cross sectional studies. (5)
- Relatively inexpensive
- Done in a short time span
- Can estimate prevalence of specified outcome – as sample taken from whole population
- Many outcomes & risk factors can be studied
- No loss to follow-up
Define the disadvantages of cross sectional studies. (3)
- Not easy to infer causal associations
- Only presents situation at one point in time – which may change
- Prevalence-incidence bias – for long-standing diseases risk factors associated with death will be under-represented
