Sampling
A phenomena may be studied using one of two approaches: taking a census, or selecting a sample.
It is often nearly impossible to census a population due do limitations of time, money and access. Therefore, the majority of time scientists study a sample of the population, selected to represent the entire population of interest. Information about the population can be estimated from the sample if the sample is large enough to reliably represent the whole population and if the sample is selected without bias.
- Census: to measure every possible member of the population
- Sample: to measure some of the members of a population
It is often nearly impossible to census a population due do limitations of time, money and access. Therefore, the majority of time scientists study a sample of the population, selected to represent the entire population of interest. Information about the population can be estimated from the sample if the sample is large enough to reliably represent the whole population and if the sample is selected without bias.
- Simple random sampling: all members of the sample are chosen at random and are equally likely to be in the sample.
- Systematic random sampling: The first member of the sample is chosen at random then the other members of the sample are taken at pre-determined intervals (i.e. every 1 meter from the starting point).
