populations and sampling

• population: everyone or everything that could be involved in the investigation e.g. when investigating opinions of students in the school.
• census: a survey of the entire population
• sample: a smaller number from the population that you actually survey.the data obtained from the sample is then used to make conclusions about the whole population,so it is important that the sample represents the population fairly.
• sampling frame- a list of all the members of the population.this is where you will choose the sample from e.g. electoral roll,school register
• sampling unit: the people that are to be sample e.g. students in a school.
• biased sample: a sample that does not represent the population fairly.Example,if surveying students at a mixed school and the sample only contains girls.avoid bias by using sampling methods.
• census-advantages- unbiased,accurate,takes into account entire population
• census-disadvantages- time consuming,expensive,lost of data to manage,difficult to ensure whole population is used.
• sample-advantages- cheaper,quicker,less data to consider
• sample-disadvantages-may be biased,not completely representative.