Cross sectional study-dr.wah

Cross sectional study-dr.wah

1. Cross-Sectional Studies Dr. Win Aye Hlaing Lecturer Department of Epidemiology University of Public Health, Yangon 1/24/2017 1

2. Types of Descriptive Study Cross-sectional (Prevalence) Study Case Report Case Series 1/24/2017 2

3. Types of Analytic Study Cross-sectional Analytic Study Cohort Case-Control 1/24/2017 3

4. Cross Sectional Studies possible relationship of increased serum cholesterol level (the exposure) to evidence of CHD ( the disease) in cross-sectional study, both exposure and disease outcome are determined simultaneously for each subject viewing a snapshot of the population at a certain point in time to imagine that we have sliced through the population, capturing levels of cholesterol and evidence of CHD at the same time we identify are prevalent cases of the disease but we do not know their duration also called a prevalence study 1/24/2017 4

5. Cross-sectional study is a study in which all the measurements are taken at a particular point in time When a study only measures health outcome , it is known as descriptive cross-sectional study When a study only measures both exposure and health outcome at the same time, it is known as analytic (comparative) cross-sectional study 1/24/2017 5

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7. Descriptive Cross-Sectional Study They provide a prevalence rate of a disease at a point in time (point prevalence) or over a period of time (period prevalence) The total population is the denominator for these prevalence rates The study describes prevalence rate by personal characteristics (e.g., age & sex), geographical areas and time frame If cross-sectional studies are done serially over a certain period, they can provide time trend of disease prevalence 1/24/2017 7

8. Analytic (Comparative) Cross-Sectional Study A cross-sectional study is an observational study in which exposure and disease are determined at the same point in time in a given population Often deal with exposures that can not change, such as blood type or other invariable personal characteristics Cases in a cross-sectional study will over represent cases with a long duration of illness and under represent those with a short duration of illness 1/24/2017 8

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10. association between increased cholesterol level and CHD, we are left with several problems First , we are identifying prevalent cases of CHD rather than incident (new) cases may not be representative of all cases of CHD 1/24/2017 10

11. Second , the presence or absence of both exposure and disease was determined at the same time in each subject it is not possible to establish a temporal relationship 1/24/2017 11

12. Cross-Sectional Studies : Example 1/24/2017 12

13. Uses of Cross-sectional Studies Assessment of Health Status of a Population Trend Analysis (by serial cross-sectional surveys) Secular trend, Cyclic changes, Seasonal variation, Epidemics Health Care Planning prioritization, target population & resource allocation Clues about Disease Causation & Prevention Hypothesis generation 1/24/2017 13

14. Cross-sectional Study Strengths Relatively feasible and not too time-consuming , since there is no follow-up period (though random sampling in a large population can be expensive and problematic) We can study several diseases and/or exposures ; thus, it is useful for screening new hypotheses We can describe disease frequency and health needs of a large population; thus, it is useful for health planning 1/24/2017 14

15. Cross-sectional Study Weaknesses Potential temporal ambiguity (exposure and disease) It is inefficient for studying rare or highly fatal diseases or diseases with short durations of expression 1/24/2017 15

16. Case reports and case series 1/24/2017 16

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19. Advantages of Case Series Useful in hypothesis formation, describing "clinical experience“ Easy and inexpensive to do in hospital settings Can constitute the case group for a case-control study Disadvantages of Case Series With no comparison group , no formal assessment of relationship b/t exposure and outcome 1/24/2017 19

20. 1/24/2017 20 THANK YOU!!