Jacy is conducting a laboratory experiment to investigate the effect of eating chocolate on mood. She predicts that eating chocolate will make people happier than not eating chocolate. She has 20 participants.

Mark scheme

Marking points from the official mark scheme (May/June 2021). The mark or mark type is shown in brackets.

1. [2] Because (she is conducting an experiment so) she can be certain that the IV is the cause of changes in the DV; And Jacy is measuring happiness, the DV, in IV conditions of chocolate or none; In experiments confounding variables are controlled so the IV must be the cause of changes in the DV; In this case the only factor affecting mood should be the eating of chocolate;
2. [1] random allocation / assignment / randomisation;
3. [3] By allocating people randomly between the two levels of the IV, different (starting) moods should be spread evenly between the two conditions;
4. [3] So no other factors / participant variables / individual differences e.g. being bad tempered affect mood;
5. [3] So people in the sample have an equal chance of being in the control group or the chocolate group to even out individual differences;
6. [2] (An independent measures design is) where different participants perform in each level of the IV; Jacy has different participants in the control and chocolate groups / participants either eat chocolate or do not;