9.2 Some basic definitions
Definition 9.1. A population is the entire group about which information is wanted — all minibuses in Lusaka, all maize farmers in Central Province, all patients at a clinic.
Definition 9.2. A sample is a subset of a population, chosen because examining every member is usually impossible.
Definition 9.3. Discrete data can take only separate, exact values, with nothing in between. The number of children in a family is discrete: it may be \(2\) or \(3\), never \(2.4\).
Definition 9.4. Continuous data can take any value in a range, and is limited only by the accuracy of the measuring instrument. Height, mass, time and temperature are continuous.
Note 9.5. The distinction is about what the quantity can be, not about what was written down. A mass recorded as \(57\) kg is still continuous data — the true mass is somewhere between \(56.5\) and \(57.5\) kg, and it was only rounded. This is why continuous data gets class boundaries ending in \(.5\) later in the chapter, and discrete data does not always need them.
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