One part of the investigation by Dement and Kleitman (sleep and dreams) involved a correlational study measuring a range of times spent in REM sleep and the number of words in the participant's dream narrative.

Mark scheme

Marking points from the official mark scheme (May/June 2020). The mark or mark type is shown in brackets.

1. [1] 1 mark for explanation (generic or linked) Because they were looking for the relationship between two variables = 1 Because they were looking for the relationship between time spent in REM and length of the narrative = 1
2. [2] 1 mark for disadvantage 1 mark for link correlations cannot find causal relationships = 1 (disadvantage) so they couldn't tell if REM sleep caused dreams / e.g. between REM and dreaming = 1 (link) the correlation was difficult to see = 1 (disadvantage) because there were only a few long REM phases = 1 (link) a correlation that was found may have been flawed = 1 (disadvantage) because the number of words in the dream narrative could depend on expressiveness = 1 (link)