The practical application of prevalence data
In this step we’re going to examine how to:
Read the information below and think about the questions asked in each section.
Identifying good sources of population information
The Gambia is a small country, situated on the West Coast of Africa. In 1986 a population-based survey of blindness was conducted throughout the whole country. This was initiated by the Ministry of Health in The Gambia in collaboration with the International Centre for Eye Health and Prevention of Blindness programme at the World Health Organization.
The purpose of the survey was to provide baseline data on the prevalence of the major blinding eye diseases.
Ensuring that appropriate information is selected
The sampling strategy involved multi-stage random sampling ( will be explained later in the course), stratified by districts north and south of the river, by urban, peri-urban and rural communities, and by settlement sizes of less than and more than 300 persons. A total sample of 8,000 people was needed.
The researchers collected data was collected using a standardized eye examination protocol which included visual acuity testing and an eye examination.
• Question C. Why is it important to use a standardised examination protocol in an epidemiological survey?
• Question D. How do you think the researcher could make sure the protocol is used by all the staff carrying out the survey?
Understanding the relevance of prevalence data
Coverage of the survey was 94%. The data estimated the prevalence of blindness less than 3/60 was 0.7%. The prevalence of low vision was found to be 1.4%.