Which ones are True? 1. A well-designed placebo allows an experiment to be conducted blind. 2. In a blind experiment, the subjects do not know whether they are in the treatment group or control group. 3. Using a random chance procedure to assign subjects to treatment or control reduces bias 4. Placebos are used so that even the people who do not receive a treatment can benefit from the study. 5. Placebos are used to randomly assign participants to treatment or control. 6. Controlled experiments can be randomized or nonrandomized. 7. In an observational study, the investigators assign the subjects to treatment or control.

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Researchers investigate how the presence of cell phones influence the quality of human interaction.  Subjects are randomly selected from a population and divided into an experimental group that is asked to leave their phones in the front of the room and a control group that are not asked to leave their cell phones at the front of the room.  Subjects are left alone for 10 minutes and then asked to take a survey designed to measure quality of interactions they had with others in the experiment.  What statistical test is appropriate?

Example: Assume that adults were randomly selected for a poll. They were asked if they "favor or oppose using federal tax dollars to fund medical research using stem cells obtained from human embryos.” Of those polled, 480 were in favor and 394 were opposed. A politician claims that people don’t really understand the stem cell issue and their responses to such questions are random responses equivalent to a coin toss. Use a 0.01 significance level to test the claim that the proportion of subjects who respond in favor is equal to 0.5. What does the result suggest about the politician’s claim? Following the hypothesis test steps, let’s first identify the claim and the null and alternative hypotheses: For this example, the original claim is that the proportion of the subjects who responded in favor is equal to 0.5 (half – since the politician compared their responses as equivalent to a coin toss). The symbolic form of the politician’s claim can be expressed as p = 0.5. Also notice…