Two changes that occur together do not necessarily explain one another. Researchers com several poss explanations bec observed patt sometimes ref hidden influ rather th direct conne between eve within t same setting. For example, both sales of cold drinks and visits to outdoor pools might rise during warm weather. Buying a drink need not cause someone to swim. A third factor can affect both activities. To understand a relationship, investigators must consider the process that could connect the observations, rather than relying on the pattern alone.

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