1. Sampling The complete set of people or objects that information is collected from is called the population. Information is normally taken from a small part of a population. This is called a sample of the population. It is important to choose the sample without bias. The sample size needs to be large enough to be representative, but small enough to be manageable

2. Sampling Random Systematic Cluster Stratified

3. Random sampling In a random sample, every member of the population has an equal chance of being selected. –Numbers chosen from a hat. –Random number tables. –Random numbers are generated using a scientific calculator.

4. Random number tables

5. Systematic sampling In a systematic sample, every member of the sample is chosen at regular intervals. A sample chosen in this way can be biased, if low or high values occur in a regular pattern.

6. Cluster sampling The population is divided into smaller groups. These smaller groups are called clusters. One or more clusters are chosen using random sampling. This is called cluster sampling. The sample is then every member of the clusters chosen.

7. Stratified sample A population may contain separate groups or stata. Each group needs to be fairly represented in the sample. The number from each group is proportional to the group size. The selection is then made at random from each group.

8. Simple Random Sampling – this gives every piece of data the same chance of being selected. Stratified Sampling – this is where you select an appropriate amount from smaller groups within the population Systematic Sampling – You use a regular pattern to select from a list Cluster Sampling – Split the population into clusters and then randomly select some cluster to sample fully. Quota Sampling – you get told how much to sample and where Convenience – ask the first 50 you meet Opinion Polls – use a combination of cluster and quota sampling Sampling

9. Stratified Sampling Example YearNumber of pupils 10198 11120 12101 A school has the number of pupils listed below in its year groups. It wishes to carry out a survey of 40 pupils. They choose to do this by stratified sampling. How many pupils from each year should they ask the survey to?

10. Stratified Sampling Year Number of pupils Fraction of school Number to be used 10198 11120 12101 Total419 A school has the number of pupils listed below in its year groups. It wishes to carry out a survey of 40 pupils. They choose to do this by stratified sampling. How many pupils from each year should they ask the survey to?

11. Stratified Sampling Year Number of pupils Fraction of school Number to be used 10198 11120 12101 Total419 A school has the number of pupils listed below in its year groups. It wishes to carry out a survey of 40 pupils. They choose to do this by stratified sampling. How many pupils from each year should they ask the survey to?

12. Stratified Sampling Question YearNumber of pupils 9225 10250 11200 A school has the number of pupils listed below in its year groups. It wishes to carry out a survey of 60 pupils. They choose to do this by stratified sampling. How many pupils from each year should they ask the survey to?

13. Stratified Sampling Solution YearNumber of pupils FractionAmount needed 9225 10250 11200 Total675 A school has the number of pupils listed below in its year groups. It wishes to carry out a survey of 60 pupils. They choose to do this by stratified sampling. How many pupils from each year should they ask the survey to?

14. Questionnaires A questionnaire is a set of questions used to obtain data from individuals. The questionnaire itself should: Be clear Start with easy questions Be obvious where the answer should be recorded Be able to be answered quickly Be as brief as possible

15. Questionnaires Individual questions should: Be short Use simple clear language Be unambiguous Be free from bias Not leading… e.g. do you agree with… Be useful & relevant