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For example, when studying age-related brain changes, including more participants at both younger and older age ranges produces more reliable findings than random sampling or concentrating on middle-aged participants.

Pollsters usually attempt to obtain a representative sample through random sampling, where everyone has an equal chance of selection.

If random sampling is possible, then correlation between individuals within clusters reduces the effective population size, which suggests biologists could collect fewer samples to predict disease prevalence.

While my random sampling of stolen checks numbered just 20, the resulting confusion was enough to leave experts scratching their heads.

“What we are seeing is more visits from AHCA, and they want to look at every patient file. They used to do a random sampling but now they want every single record,” Gallagher said.