Using controls

Question 1

Describe what is meant by a control group

Answer 1

- A control group is a standard to be compared with the experimental condition

Question 2

What are control groups used for

Answer 2

• The control group can be used to show the effect of a particular variable

Question 3

Explain how placebos act as a control in a drugs trial

Answer 3

• Placebos are substances that look and taste like the real drug, but do not contain the active ingredient.
• Placebos are used as a comparison, to show that the active ingredient is the thing having an effect rather than any psychological effect

Question 4

What are double blind trials and why are they used

Answer 4

• In double blind trials, neither the participant nor the scientist know which group has the placebo.
• Double blind trials reduce the chance of bias affecting the results

Question 5

Scientists investigated the effect of taking omega-fatty acids in fish oil on heart rate during exercise. They recruited two large groups of volunteers, A and B. For each group, they measured the mean heart rates at different intensities of exercise. The volunteers were then given capsules to take for 8 weeks.
Group A was given capsules containing omega-3 fatty acids in fish oil.
Group B was given capsules containing olive oil.
Group B was given capsules containing olive oil.
Explain why.

Answer 5

- To ensure results are due to omega-3/fatty acids (only)/ not due to something else in the oil;
Neutral: Idea of comparing groups/
results
- Placebo linked to mental / psychological effect;
Neutral: reference to a control group/ placebo (unqualified)

Question 6

Scientists investigated the effect of drinking tea and coffee on reducing the risk of developing one type of brain cancer. The investigation involved 410 000 volunteers and was conducted in 10 European countries over a period of 8.5 years.
Another group of scientists investigated the effect of caffeine on blood flow to certain parts of the brain. Volunteers were given different concentrations of caffeine solution to drink. A control group was also set up.

(i) Describe how the control group should have been treated.

Answer 6

1.Treated the same;
2. Accept decaffeinated
2. No caffeine;
2. Reject placebo.