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3 cross sectional study
- 1. Cross Sectional Study Prof. Wei-Qing Chen MD PhD Department of Biostatistics and Epidemiology School of Public Health 87332199 [email_address]
- 14. Measure: Prevalence Example: RQ: What is the prevalence of chronic pain after hernia surgery? Exposure of interest : Hernia surgery Outcome of interest : Chronic pain (lasting for more than 3 months) Methods: questionnaire survey Sample: All patients who had a hernia procedure between 1995-1997 n=350 Results: Period prevalence chronic pain = 30% (CI 95% 24 - 36%) Point prevalence chronic pain = 25% (on day of survey)
- 17. Design of cross-sectional survey
- 19. Study Design Exposure (Risk Factor) Disease (Outcome) + + _ _
- 46. Analysis Grape Tomato Prevalence ratio = 52% / 19% = 2.6 (+) (–) DZ = Rash 183 43 95 88 8 35 (19%) (52%)
Notas do Editor
- This lecture seeks to provide you with a basic understanding of Cross-Sectional Studies, the most common observational study used by Epidemiologists. Additional textbook resources can be found in the following annotated bibliographies on my Web site: <UL> <LI><B><A HREF= “http://www.bettycjung.net/Biostats.htm”> Annotated Biostatistics Bibliography </A></B></LI> <LI><B><A HREF= “ http://www.bettycjung.net/Epi.htm”>Annotated Epidemiology Bibliography </A></B></LI> <LI><B><A HREF=“http://www.bettycjung.net/Methods.htm”>Annotated Research Methods</A></B></LI> <LI><B><A HREF=“http://www.bettycjung.net/Research.htm”>Annotated Research Practice (A - L)</A></B></LI> <LI><B><A HREF=“http://www.bettycjung.net/Researc1.htm”>Annotated Research Practice (M - Z)</A></B></LI> <LI><B><A HREF=“http://www.bettycjung.net/Stats.htm”>Annotated Statistics Bibliography </A></B></LI></LI></UL> Sources for this lecture include: L, Gordis (1996) Epidemiology , R.M. Page, G.E. Cole & T.C. Timmreck (1986) Basic Epidemiological Methods and Biostatistics , and W.H.O. (1990) Basic Epidemiology .
- Cross-Sectional studies are examples of applied research. Applied research is probably THE research approach taken by Public Health Practitioners in the course of their work. Because Public Health seeks to ensure the health of the Public, it does this by first trying to prevent problems before they occur. This is what Prevention is all about. And, if a problem has already occurred, Public Health Practitioners work hard to control the situation. If it affects a lot of people, and public health interventions, strategies, programs can address the problem, then surveillance systems will be developed and maintained. These systems help to keep the problem under control, by monitoring the problem as well as providing data to evaluate the effectiveness of the solutions (interventions, strategies, programs). These strategies seek to prevent the problem from occurring again. In fact, Public Health has been so successful in ensuring the Public’s health that it is sometimes taken for granted, until some disaster occurs. As a result, public health programs don’t always get the funding they can really use to remain vigilant. These issues are ones of Public Health Infrastructure, which Healthy People 2010 (US Public Health Service planning document) does address. So, in order to conduct applied research in Public Health, I think it is essential that there is an infrastructure that supports this type of research so Public Health can fulfill its mission to ensure the health of the Public.
- Ottawa ankle rule. XR if age > 55 yrs, unable to wt bear and bone tenderness on maleolus.
- NB Prevalence versus incidence (get over time) Relative prevalence - prev in group with RF compared to those without,
- Interpretation of data from a cross-sectional study such as this one must keep in mind a number of considerations. First, cross-sectional studies provide data on prevalence, not incidence. If incidence is our real interest, as it generally is for etiologic research, prevalence may not be a good surrogate. An important problem with prevalence data is that cross-sectional studies include only “survivors” and “stayers”. Rapidly fatal conditions will be greatly underrepresented in a cross-sectional study, compared to the total number of people who are affected during a given time interval. Also, conditions and characteristics associated with outmigration will also be underrepresented. In addition, for associations where causation is a possibility, it may be difficult to determine whether the “cause” preceded the “effect”. With the HIV seroprevalence survey there is the additional uncertainty about what population to apply the results to. Since a major objective in this instance was to find out if heterosexually-acquired HIV was present in NC, generalizability was less of a concern. Even so there was naturally interest in knowing whether these results might be mirrored in other STD clinics in the state, both in terms of the seroprevalence figures and also the associations, as well as whether these results would be similar in other subpopulations, such as injection drug users.
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- Is there systematic increase or decrease of RF? Is there systematic increase or decrease of RF? Child care increases liklihood of going to MDs office. NSSP increases liklihood of going to MDs office. Does child care increase risk of NSSP? Prevalence incidence bias. HLA-A2 affects survaival of children with leukaemia, not a RF for poor prognosis.