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7 
Sampling methods What different sampling methods are possible? What are the advantages and disadvantages of each method? Remember the aim: The sample must be representative of the population Once we have a sample the data should be checked for errors (cleaned data) Description of sampling method and justification of sampling method choice (practice) 

For AS 2.9 you need to know about different sampling methods Discussion of sampling methods (for statistical insight rather than execution) 

Description 
Advantages 
Disadvantages 




In the assessment do a simple random sample (discuss how)


Reasons for sampling: Include time and cost considerations, lack of access to the entire population and the nature of the data collection or test, eg: A blood test verses the breaking strain of fishing line. Features of a good sample, There is no statistical requirement that a sample be a proportion of the population; a well designed sampling process is more likely to produce a representative sample than a large sample poorly selected sample. It is randomly chosen: each member of the population has the same chance of being included in the sample. Cleaning the data checks for data errors (eg 3.4m or 340cm) 