A student’s study found a strong correlation between grip strength and VO₂max.

Outline why the student should treat their results with caution.

Explain how the following study design element can be applied in an experimental method: control group.

Explain how the following study design element can be applied in an experimental method: placebo.

there is no justification for the two to be related ✔

a correlation can be used to see whether there is a relationship/connection between the change in one variable and another ✔

a correlation does not necessarily indicate that the changes are causal e.g. grip strength and VO₂max may be correlated but that does not mean that the increase of one causes the other ✔

other variables may be acting on one or both of the related variables (and affecting them in the same direction) ✔

Credit reference to internal validity only once.

the control group is the group that does not receive the treatment ✔

e.g. if a study was investigating the effect of warm-up on performance the control group would not complete a warm-up ✔

control group allows comparison point for independent variable / internal validity✔

a placebo is a substance / piece of equipment which in every way appears to be like the real substance / equipment being tested ✔

e.g. a study into the effect of sugar on reaction times could use a pill that looks and tastes like the sugar pill being tested but is not sugar ✔

treatment and control groups are assigned randomly ✔

groups are compared pre- and post- testing ✔

Poorly answered question, most candidates found this a difficult question to answer and did not understand what was expected of them. The most common response was that 'correlation does not mean causation'. Few candidates were able to make a second valid point. 

Candidates have a good understanding of why a study design has a control group, but few candidates were able to explain how a control group is used within a study. Most candidates referred to control groups being used to compare groups. However very little scientific terminology, such as 'independent variable', were used. 

Similarly to 6(b)(i), many candidates were unable to explain how a placebo is applied to the study design. Many answers were vague and lacked scientific language.