1. Statistics

2. Definitions
A statistical study targets a set of people, objects or events called a population.
More specifically, studies deal with characteristics:
Quantitative or Qualitative variables.
A sample is a subset of a population. The size of a sample is the number of elements it contains.’
A sample is representative when it has the same characteristics as the population.

3. MAIN TYPES OF STATISTICAL STUDIES.
Census : A census is a statistical study in which the entire population (every member) is analysed using different variables. It is a measuring instrument for which the degree of certainty is high, but it requires on a tremendous amount of resources  human, material and financial.

4. MAIN TYPES OF STATISTICAL STUDIES.
Poll: A poll is a statistical study in which a sample of a population is analysed so that conclusions can be drawn concerning the whole population. Despite a degree of uncertainty, a well-conducted poll offers a sufficiently accurate picture of the situation. It is used when the target population is too dense or inaccessible.

5. MAIN TYPES OF STATISTICAL STUDIES.
Study: A more complete statistical study usually involving experts and various data-gathering methods is called a study. The latter is used when polls or censuses are insufficient or inadequate.

6. Collection Methods
 a written questionnaire, that a person fills out and returns to the poll
 a telephone interview,in which the pollster asks questions on the telephone
 a face-to-face interview, often takes place in public
 direct observation, in which the pollster, using an observation grid, records events or the behaviour of people
documentary observation, in which the data are collected to create a database
the use of mechanical or electronics devices and instruments