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Cross-sectional study. 1. . Definition. A cross-sectional studies a type of observational or descriptive study the research has no control over the exposure of interest (e.q. diet). It involves identifying a defined population at a particular point in time

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definition

1.

Definition
  • A cross-sectional studies
    • a type of observational or descriptive study
    • the research has no control over the exposure of interest (e.q. diet).
  • It involves
    • identifying a defined population at a particular point in time
    • measuring a range of variables on an individual basis
    • include past and current dietary intake
uses of cross sectional studies
Uses of cross-sectional studies
  • Prevalence survey: The studies are commonly used to describe the burden of disease in the community and its distribution.
  • Describe population characteristics: They are also commonly used to describe population characteristics, often in terms of person (who?) and place (where?)
    • .e.q.
    • The British National Diet and Nutrition Survey or Nutrition and Health Survey in Taiwan
    • To describe various age groups in the population in terms of food and nutrient intake and range of other personal and lifestyle characteristics.
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Migrant study : Some migrant studies may full into the classification of cross-sectional studies. These studies give clues as to association between genetic background and environmental exposures on the risk of disease.
    • e.q. A study of the prevalence (percentage) of coronary heart disease
    • among men of Japanese ancestry living in Japan, Honolulu and the San Francisco Bay area
    • showed the highest rates among those who had migrated to the United States.
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KAP (knowledges, attitudes, and practices ) study:
    • KAP studies are purely descriptive and help to build up a better understanding of the behavior of the population, without necessarily relating this to any disease or health outcome.
  • Management tool: health service managers and planners may make use of cross-sectional survey to assess utilization and effectiveness of service.
  • Development of hypothesis: Hypotheses on the causes of disease may be developed using data from cross-sectional study survey.
limitation of cross sectional study
Limitation of cross-sectional study
  • It is not possible to say exposure or disease/outcome is cause and which effect.(不能判定因果關係)
  • Confounding factors may not be equally distributed between the groups being compared and this unequal distribution may lead to bias and subsequent misinterpretation.
  • Cross-sectional studies within dietary survey, may measure current diet in a group of people with a disease. Current diet may be altered by the presence of disease.
  • A further limitation of cross-sectional studies may be due to errors in recall of the exposure and possibly outcome.
design of cross sectional survey
Design of cross-sectional survey
  • The problem to be studied must be clearly described and a thorough literature review undertaken before starting the data collection.
  • Specific objectives need to be formulated.
  • The information has to be collected and data collection techniques need to be decided.
  • Sampling is a particularly important issue to ensure that the objectives can be met in the most efficient way.
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Fieldwork needs planning:
    • Who is available to collect the data ?
    • Do they need training ?
    • If more than one is to collect the data then it is necessary to assess between-observer variation.
  • The collection, coding and entry of data need planning.
  • A pilot study is essential to test the proposed methods and make any alternations as necessary.

* The steps are summarized in Fig 13.5*

dietary assessment in cross sectional studies
Dietary assessment in cross-sectional studies
  • Some characteristics of dietary assessment methods for cross-sectional studies
    • Measures an individual’s intake at one point in time.
    • Does not require long-term follow up or repeat measures
    • Valid
    • Reproducible
    • Suitable
    • Cost within study budget
dietary method application
Dietary method application
  • Food records using household measures have been used in cross-sectional studies.
  • The recall method attempts to quantify diet over a defined period in the past usually 24 hours.
  • The most commonly used dietary assessment method which attempts to measure usual intake is the food frequency questionnaire (FFQ).
analysis of cross sectional study
Analysis of cross-sectional study
  • Before starting any formal analysis, the data should be checked for any errors and outlines.
    • Obvious error must be corrected.
    • The records of outliners should be examined excluded
    • Checking normality of data distribution.
      • e.q. using the Kolmogorov-Smirnov Goodness of Fit Test.
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Standard descriptive statistics can then be used: mean, median, quartiles, and mode; measure of dispersion or variability such as : standard deviation; measure precision such as: standard error, and confidence intervals.
  • Mean can be compared using t-tests or analysis of variance (ANOVA).
  • More complex multivariate analysis can be carried out such as multiple and logistic regression.