Health surveys are based on probability samples of defined populations.
Interviewers who are not care givers approach households, providers or patients and compile information using a structured protocol.
An advantage of this procedure is that it collects information that can be projected to estimate the conditions, care and results for a defined population.
Surveys use the same protocol for each member of the sample—thereby improving the validity of comparisons.
A disadvantage is that the structured protocol may not allow interviewers to compile the full array of information needed to replicate the actual diagnoses or treatment records obtained from clinical observations.