In the study by Yamamoto et al. (chimpanzee helping), the researchers needed a reliable procedure for testing the tool choice made by the chimpanzees.

Mark scheme

Marking points from the official mark scheme (May/June 2019). The mark or mark type is shown in brackets.

1. [1] 1 mark for definition
2. [1] 1 mark for linked example
3. reliability is about consistency = 1 mark
4. to be reliable, measures must measure the phenomenon in the same way each time = 1 mark
5. e.g. Yamatoto et al standardised the procedure, e.g. by always having the same 7 objects on the tray (as tools) at the start of a trial / trial always ended after 5 min if not appropriate tool transfer / maximum of 4, minimum of 2 trials per day / had 3 video cameras / only counted the first tool offered etc. = 1 mark for example
6. They made sure researchers measured helping in a similar way, i.e. were reliable, by using the same rules such as only counting the first tool offered = 2 marks
7. [1] 1 mark for identifying problem. (This can also be linked but does not have to be)
8. [1] 2nd mark for linked detail
9. There was a range of number of trials per day (maximum of 4, minimum of 2); (1 for identification)
10. So some chimps may have been more familiar/ less willing as they had had more / less trials; (1 for link)