S3 June 2009 Q1
1. A telephone directory contains 50 000 names. A researcher wishes to select a systematic sample of 100 names from the directory.
(a) Explain in detail how the researcher should obtain such a sample. (2)
(b) Give one advantage and one disadvantage of
(i) quota sampling,
(ii) systematic sampling. (4)
| Scheme | Marks |
|---|---|
| Randomly select a number between 00 and 499 (001 and 500) | B1 |
| select every 500th person | B1 |
| (2) |
Notes
1st B1 for idea of using random numbers to select the first from 1 - 500 (o.e.)
2nd B1 for selecting every 500th (name on the list)
If they are clearly trying to carry out stratified sample then score B0B0
| Scheme | Marks |
|---|---|
| (i) Quota Advantage: Representative sample can be achieved (with small sample size) Cheap (costs kept to a minimum) not “quick” Administration relatively easy | B1 |
| Disadvantage Not possible to estimate sampling errors (due to lack of randomness) Not a random process Judgment of interviewer can affect choice of sample – bias Non-response not recorded Difficulties of defining controls e.g. social class | B1 |
| (2) | |
| (ii) Systematic Advantage: Simple or easy to use not “quick” or “cheap” or “efficient” It is suitable for large samples (not populations) | B1 |
| Disadvantage Only random if the ordered list is (truly) random Requires a list of the population or must assign a number to each member of the pop. | B1 |
| (2) | |
| (6 marks) |
Notes
Score B1 for any one line
(i) 1st B1 for Quota advantage
2nd B1 for Quota disadvantage
(ii) 3rd B1 for Systematic Advantage
4th B1 for Systematic Disadvantage