I am getting way to academic here, but from this book
A population is
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The collection of all outcomes, responses, measurements, or counts that are of interest
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Obviously nobody has such information as not all gun uses are even recorded. The next best thing is to take a sample which is
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A subset of the population
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The book goes on to say
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Sample data can be used to form conclusions about populations. Sample data must be collected using an appropriate method, such as random selection. If it is not collected using an appropriate method, the data are of no value
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The Italics are the authors and not mine. This is chapter one page 5. It is harder to use stronger language than "of no value"