First, let define and distinguish the terms Population, and Sample

– If the data consist of all possible observations of a certain phenomenon, we call it Population

– If the data contains only a part of these observations, we call it Sample

Often, we need to represent a set of data in terms of a single (or a few) number

These are what we usually call Descriptive Statistics

Which kind of number we choose depends on the particular characteristics we

want to describe

- We start considering those measures which describe the center or middle of a set of

data, the measures of Central Location

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