Veterinary Epidemiology and Zoonosis

CROSS-SECTIONAL STUDIES (PREVALENCE, SURVEY)

• It is the simplest form of an observational study.
• It is based on the single examination of a cross section of population at one point in time and these things can be applied to the entire population. This study is more useful in chronic cases than short-lived cases.
• It is also known as prevalence study because prevalence can be obtained through this study. But this study does not give much information about the natural history of a disease and also incidence rate.
• This study investigates relationship between disease (or other associated health-related factors) and hypothesized causal factors in a specified population during a specified period of time.
• Animals are categorized according to the presence or absence of disease and hypothesized causal factors.
• Inference can be made about the association between the disease and the hypothesized causal factors.
  • Example: Heart valve incompetence (disease) and breed (factor).
• Technically cross-sectional studies provide a snap shot of events at a particular time.
• The point of time may range from instant to longer periods although all are treated as static point in time events.
• For the purpose of causal interpretation, cross-sectional studies are best suited to study the permanent factors such as breed, sex or blood type.
  • Example: Questioner based surveys. Studies relating to ancillary data to the results of immunologic, bacteriologic or toxicologic and slaughter house surveys.

Advantages

• Disease prevalence and proportions in the exposed and unexposed populations can be estimated.
• Relatively quick to mount and conduct.
• Inexpensive.
• Current records  can be used occasionally.
• No risk to subjects.
• Allow study of multiple potential cause of disease.

Disadvantages

• Unsuited for the study of rare diseases.
• Unsuited for the study of diseases of short duration.
• Control of extraneous variables may be incomplete.
• Incidence in exposed and unexposed cannot be estimated.
• Temporal sequence of cause and effect cannot be determined.