Population – Sample - Variable

Teaching – 10 sessions of 1H30 • Beforethelecture

– Review the book chapters posted on MyICN

• During the lecture

– Rapid presentation of the underlying theory – In-class exercises

• Afterthelecture

– Answer the remaining questions – Collect data

Session 01 Data and variables

Population – Sample - Variable

Population and sample

The set of all the elements (sometimes called statistical units, individuals or observations) we work on in statistics is called statistical population or simply population.

The total number of elements of a statistical population is called the size of the population, denoted by N.

Examples of populations :

the employees of a company, the companies of the CAC40, the inhabitants of a city, the pupils of a school or of a class, the set of all items produced by a machine during a given period, etc.

Sampling and samples

In practice it is often impossible to study the whole population. The reasons are :

•very high costs,

•the population is not completely known ,

•The inquiry takes too much time, etc.

In these cases we consider only a subset of the population called sample and

the selection procedure of the elements is called the sampling method.

The sampling consists of selecting, in a reference population or underlying population, a subset of elements – individuals, objects or cases – which are supposed to represent the population. A sample must be representative for its population.

The sample is caracterized by its size, denoted by n.

Sampling methods/procedures

Sampling Mehods

Convenience

Non- probability

Judgmental

Snowball

Probability

Simple Systematic Random

Sampling methods/procedures

• Non-probability sampling – sampling technique that does not use chance selection procedure but rather rely on the personal judgment of the researcher

• Probability sampling – a sampling procedure, in which each element of the population has a fixed probabilistic chance of being selected in the sample



The statistical characters

The elements of a given population have a certain number of characteristics called statistical characters.

Example:

In the case where the population is the set

...