Bella is conducting a laboratory experiment to find out about people's fear of animals. She asks each participant if they have any phobias. If the participant says yes they are asked to leave. The remaining participants are shown photographs while their pulse rate is measured. The independent variable (IV) is whether the photographs are of animals with eight legs or animals with four legs.

Mark scheme

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

1. [2] 1 mark for identification/description of ethical guideline 'protection from harm' 1 mark for detail otherwise they could have been distressed by the pictures = 1 (detail) to avoid participants who would have been very scared doing the study = 1 (detail)
2. [1] 1 mark for reason (explanation or term) To avoid order / practice / fatigue effects; Otherwise participants might have been so scared by the 8-legged things they even found 4-legs scary;
3. [2] 1 mark for identifying advantage (can be generic) 1 mark for link reduces individual differences = 1 (generic) in an independent measures design all the people who don't like 8-legs might be in one group = 1 (link) the same group is tested on both species, so if some people dislike all animals it doesn't matter = 1 (link)
4. [4] 1 mark for identification of extraneous variable x 2 1 mark for detail × 2 The individual's previous experience with animals = 1(identification) Whether the participants own an 8/4 legged pet = 1 (identification) If a person owns a 8/4 legged pet they would be more positive towards them = 1 (detail) Whether participants have even been bitten by a 8/4 legged animal = 1 (identification) If a person has been bitten by a cat/spider they would be more negative towards them = 1 (detail) Whether participants live in an area with feral mammals/ dangerous 8-legged animals = 1 (identification) If there is a problem with local 8/4-legged animals they would be more negative towards them = 1 (detail)
5. [2] 1 mark for identifying disadvantage (can be generic) 1 mark for detail It only produces numerical / quantitative data = 1 (identification) So Cara and Bella cannot know how the participant really feels = 1 (detail) It only produces data about their physiological response = 1 (identification) whereas the emotional response might be different = 1 (detail)