Dr. Wilkins randomly assigns subjects to one of two groups. He is interested in the effects of caffeine on anxiety levels. He gives subjects in the first group an extra two cups of coffee a day for six months. The second group receives an extra two cups of decaffeinated coffee a day for the same time period. Importantly, subjects do not know whether they are being given regular or decaffeinated coffee. By providing one group with decaffeinated coffee, Dr. Wilkins is trying to account for which potential element of the experiment?

The placebo effect

Explanation:

The placebo effects is an improvement in the area of health and behavior that is measurable and cannot be attributed to a treatment or medication. From the example in the question, coffee drinking may cause participants to become anxious, just because they are of the belief that coffee would make them anxious. Hence the decaffeinated coffee would not allow the subjects know the type of Coffee they are taking, this can help Dr. Wilkins to control this effect.

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modern american cars are not available due to trade restrictions

giant impact theory - the moon was formed from the collision between earth and another mars-sized body.

colliding planetesimals hypothesis - the moon was formed from the same cloud of material as earth.

capture hypothesis - the moon was locked into orbit by earths gravity as it was passing by it.

accretion hypothesis - the moon was formed from collisions and combining of planetesimals.

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