Negative Controls

What was Dr. Johnson's initial hypothesis about caffeine?

• Caffeine decreases blood pressure

• Caffeine variability depends on the person

• Caffeine increases blood pressure

• Caffeine has no effect on blood pressure

Why was the initial experiment considered flawed?

• Use of decaffeinated coffee

• Incorrect blood pressure measurement

• Lack of a control group

• Too many participants

What did the revised experiment include to improve the study?

• All participants drank caffeinated coffee

• Increased number of cups of coffee

• Introduction of a decaffeinated coffee group

• Only water was given to participants

What additional control was introduced in the refined experiment?

• No controls were used

• Participants drank water

• Participants were given tea

• Participants drank energy drinks

What was the final conclusion about the effect of caffeine on blood pressure?

• Caffeine significantly increases blood pressure

• Caffeine has no effect on blood pressure

• Caffeine decreases blood pressure

• Results were inconclusive