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Many people start their day with a jolt of caffeine from coffee or a soft drink.

Many people start their day with a jolt of caffeine from coffee or a soft drink. Experts agree that people who consume large amounts of caffeine each day could suffer physical withdrawal symptoms if they stop ingesting their usual amounts of caffeine "cold turkey," or all at once. A study from Johns Hopkins University in Baltimore, MD, asked if there was evidence in some people of a more serious addiction called caffeine dependence syndrome.

Twenty-seven volunteers were recruited through newspaper ads seeking people who believed they were psychologically and/or physically addicted to caffeine, but otherwise in good health. Of those 27 volunteers, 16 were diagnosed as being caffeine dependent, meaning that they exhibited signs of being physically addicted to caffeine (such as headaches, irritability, depression, muscle pain or cramping, anxiety, and/or dizziness). Of those 16 volunteers, 11 agreed to participate in a study on caffeine withdrawal. Caffeine withdrawal is the process or act of reducing or eliminating caffeine consumption.

Researchers measured each person's daily caffeine intake using that person's food diary. The experiment was conducted in two 2-day periods; each 2-day session was separated by 1 week. During one session, subjects received a set of capsules containing the amount of caffeine they normally consumed in one day. During the other session, subjects received placebos, which are capsules that look like the caffeine capsules but have no caffeine in them. The order in which each subject received the two different capsules was randomized. Reactions to caffeine withdrawal were noted using a questionnaire given to participants at the end of each study period.

The results of the study showed that 9 out of the 11 volunteer subjects exhibited withdrawal symptoms when they took the placebo. Symptoms the subjects exhibited were headaches, irritability, depression, muscle pain and cramping, anxiety, and/or dizziness. According to one researcher, "Caffeine exhibits all the features of a typical psychoactive substance that creates dependence, which had a significant impact on our subjects." In summary, the researchers suggested that the Food and Drug Administration (FDA) consider classifying caffeine as a dangerous substance. Also, the researchers noted that any products containing caffeine must have their access and distribution strictly controlled, specifically through local pharmacies using a doctor's prescription.

What research question was investigated?

What design type was used: observational, experimental, or qualitative?

How were subjects selected (or not selected) for the study? What (if any) impact did that process have?

What role did randomization play in this study? Specifically, did the researchers use randomization when selecting subjects for the study or when selecting the order in which the caffeine/placebo were given to the subjects?

In the study, neither the subjects nor the experimenters interviewing the subjects knew if the subject was receiving the caffeine pills or the caffeine free pills. Why might this be an important design element in the study?

The subjects' daily caffeine intakes were measured by evaluating their food diaries, where they recorded everything they consumed in one week's time. What potential biases could there be in this type of record that would affect the caffeine intake measurement?

Were the conclusions of the researchers reasonable considering the results of the study? Why or why not?

Is there anything in this study that leads you to believe that it lacks validity?

I came up with some answers but I'm not sure if they are correct

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