Types of data
There are two main types of data:
Quantitative
The answer is a number. Examples: number of brothers, height,....
Quantitative data can be discrete or continuous:

"Discrete data" has an exact value. Example: number of brothers.
"Continuous data" can take any value, or it may be between two possible values. An example is the height.

Qualitative
The answer is a word. Examples: hair's colour, civil status,....


Population an sample

All statistic study refers to a group of people or things called population.
The population's components are called individuals.
As it is not always possible to observe the total population, a part of the population is chosen.
It is called sample and the sample's election is very important because it has to be representative
of the total population.
The number of elements in a sample is called size.

EXAMPLES:

Situation: You are carrying out a survey on homework. You have to select a sample and ask 100 students.

There are (POPULATION):

1 ESO	80
2 ESO	100
3 ESO	140
4 ESO	80

Calculate the number of students you will ask for each group (the sample)

Total = 80+100+140+80=400

SAMPLE:

1 ESO	20
2 ESO	25
3 ESO	35
4 ESO	20