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A cross-sectional
study (also called a prevalence survey) measures the prevalence
of a symptom, determinants of a symptom, or both, in a population
at one point in time or over a short period of time. It provides
a snapshot of the health experience of a population at a given
time. Such information can be very useful in assessing the health
status and needs of a population. It can also be used to study
the relationship between variables (for example between breathlessness
and lung metastasis). The prevalence of a problem, rather than
the incidence, is recorded in a cross-sectional survey, and every
association should be interpreted cautiously. Bias may arise because
of selection into or out of the study population. For example,
in a hospital survey, patients staying for a shorter period in
hospital have less probability of being included in a cross-sectional
survey.
Problem
8.1
Figure
8.1 shows five patients over 6 days. The lines represent time
spent in the hospital. For example, patient 1 entered hospital
on day 4. A cross sectional survey takes place at day 3.
| Figure
8.1: Time Spent in a Hospital
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|---|
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Question
8.1
| On how
many patients will the survey be collected? |
 2 |
 3 |
 4 |
Question
8.2
| If the
survey were collected on day 5, or day 2, how many patients
would be included? |
| 2 |
| 3 |
| 4 |
Question
8.3
| Would
these be the same patients? |
| Yes |
| No |
|