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220905P - STUDY DESIGN 2: CROSS-SECTIONAL STUDY

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Presented at a Webinar on Research Methodology in Health Sciences at Northern Area Armed Forces Hospital (NAAFH) on 5th September 2022. By Professor Omar Hasan Kasule Sr.  MB ChB (MUK). MPH (Harvard), DrPH (Harvard) Professor of Epidemiology and Bioethics 


LEARNING OBJECTIVES:

  • Cross-sectional studies: Definition and types (ecologic, prevalence, surveys).
  • Cross-sectional studies: Design, analysis, and interpretation.
  • Cross-sectional studies: Strengths and weaknesses.


KEYWORDS AND TERMS:

  • Cross-sectional study
  • Prevalence study
  • Ecological Study
  • Prevalence of the disease
  • Prevalence of the risk factor


DEFINITION OF A CROSS-SECTIONAL STUDY:

  • The cross-sectional study is also called the prevalence study.
  • Its objective is the determination of the prevalence of risk factors and the prevalence of disease at a point in time (calendar time or an event like birth or death).
  • Disease and exposure are ascertained simultaneously.


TYPES OF CROSS-SECTIONAL STUDIES:

  • A cross-sectional study can be descriptive or analytic or both.
  • It may be done once or may be repeated.
  • It may be that Individual-based studies collect information on individuals.
  • It may be group-based (ecologic) studies collecting aggregate information about groups of individuals.


USES OF CROSS-SECTIONAL STUDIES:

  • Community Diagnosis
  • Preliminary study of disease etiology
  • Assessment of health status
  • Disease surveillance
  • Public health planning
  • Program evaluation.


ADVANTAGES OF CROSS-SECTIONAL STUDIES:

  • Simplicity,
  • Rapid execution to provide rapid answers.


DISADVANTAGES OF CROSS-SECTIONAL STUDIES:

  • Inability to study etiology because the time sequence between exposure and outcome is unknown.
  • Inability to study diseases with low prevalence.
  • High respondent bias.
  • Poor documentation of confounding factors.
  • Over-representation of diseases of long duration.


DESIGN OF A CROSS SECTIONAL STUDY: 2x2 TABLE:


STATISTICAL PARAMETERS:

  • The following descriptive statistics can be computed from a cross-sectional study: mean, standard deviation, median, percentile, quartiles, ratios, proportions, the prevalence of the risk factor, n1/n, and the prevalence of the disease, m1/n.
  • The following analytic statistics can be computed: correlation coefficient, regression coefficient, odds ratio, and rate difference.