#statistics 

**Population** - any complete collection of observations or potential observations.

**Sample** - any smaller collection of actual observatiosn from a [[Data|population]].

***A sample must represent a population***.

## Population types
**Real population** - a population in which all potential observations are accessible at the time of sampling. E.g.: the ethnic backgrounds of all current employees of the U.S. Postal Department

**Hypothetical population** - a population in which not all potential observations are accessible at the time of sampling.

![[Pasted image 20230915172456.png]]

## Types of procedures used to collect a sample from a population
**Random sampling** - a procedure designed to ensure that each potential observation in the population has an equal chance of being selected in a survey (for large populations)

This randomness describes *the selection process*, and not the particular pattern of observations in the sample.
Casual / haphazard sample != random
Use random number tables/books

**Random assignment** - a procedure designed to ensure that each person has an equal chance of being assigned to any group in an experiment. (for small populations)
Also use random number tables/books

![[Pasted image 20230713124220.png]]