Kaleem is planning to investigate sleep and dreaming. He needs to find participants.

Mark scheme

Marking points from the official mark scheme (May/June 2018). The mark or mark type is shown in brackets.

1. 1 mark for identifying a representative sampling method (accept random, systematic, stratified). Plus 1 mark for detail.
2. random sampling; chosen so that each person in the population has an equal chance of being in the sample; e.g. giving every member of the population a number, putting them in a hat and selecting the first numbers/people who come out of the hat;
3. 1 mark for identification of a feature × 2
4. age (range);
5. gender (ratio);
6. recall of dreams;
7. sleep patterns;
8. health;
9. drinking habits;
10. work pattern;
11. 1 mark for identifying why the variable is important. 1 mark for elaboration/justification.
12. age: older/younger people might dream more/less; so an age-biased sample will be less valid/if all 'dream less' age, the sample of dreams will be small;
13. gender: males/females might dream more/less; so a gender-biased sample will be less valid;
14. whether they normally recall their dreams: if they do not, they will not be able to report dreams to Kaleem; so it will be difficult to collect data/the data will be less valid;
15. whether they normally drink alcohol: if they do, this could reduce the amount of REM sleep; so they will dream less than participants who do not normally drink alcohol;
16. whether they normally drink caffeinated drinks/coffee: if they do, this could reduce the amount of sleep; so they will dream less than participants who do not normally drink caffeinated drinks/coffee;