Study design #2 - Questions and Answers

Question 1 Who is more likely to binge drink-male or female college students? The Harvard School of Public Health surveys random samples of male and female undergraduates at four-year colleges and universities about whether they have engaged in binge drinking. What type of study design is being used to produce data? Answer An experiment deliberately imposes some treatment on individuals in order to observe their responses. An observational study tries to gather information without disturbing the scene they are observing. Observational study Thus we have an observational study that will compare the proportions of two samples orienting from two independent populations. Note: The exercise prompt mentions that they "survey" random samples. However, this does not mean that the study is a survey, because the definition of a survey is "a general view, examination, or description of someone or something", thus it is possible that the data is collected by observing people and thus also WITHOUT specifically asking people questions, which means that the study is not necessarily a survey. Question 2 Refer to the Journal of Experimental Social Psychology (Vol. 45, 2009) study of whether buying gifts truly buys love. Recall that study participants were randomly assigned to play the role of gift giver or gift receiver. Gift receivers were asked to provide the level of appreciation (measured on a 7-point scale where 1 = "not at all" and 7 = "to a great extent") they had for the last birthday gift they received from a loved one. Gift givers were asked to recall the last birthday gift they gave to a loved one and to provide the level of appreciation the loved one had for the gift. The researchers wanted to know if the average level of appreciation is higher for birthday gift givers than for birthday gift receivers. a. Why is this study designed? b. Specify the key elements of the study: experimental unit, response variable, factor, and treatments. Answer (a) A designed study (experiment) deliberately imposes some treatment on individuals in order to observe their responses. An observational study tries to gather information without disturbing the scene they are observing. The participants were randomly assigned to play the role of gift giver or gift receiver. This then implies that the treatments gift giver" and "gift received" were imposed on the individuals, thus the study is a designed studty. (b) The experimental units are the individuals on whom an experiment is performed. Experimental units=Study participants A response variable (or dependent variable) is a variable that measures an outcome or result of a study. Response variable=Level of appreciation of gift The factors are variables whose levels are manipulated hy the experimenter and thus these variables are controlled by the experimenter. Factors: Giver or receiver The treatments are what the subjects are subjected to. Treatments: Giver and Reciever. Question 3 Define the following terms: a. Observational study, b. Designed experiment. Answer (a) In an observational study, researchers simply observe characteristics and take measurements, as in a sample survey. These reveal only association. (b) In a designed experiment, researchers impose treatments and controls and then observe characteristics and take measurements. These can help establish causation. Question 4 What is the difference between an observational and a designed study? Answer A designed study is an experiment in which the analyst controls the specification of the treatments and the method of assigning the experimental units to each treatment. An observational study is a study in which the analyst simply observes the treatments and the response on a sample of experimental units.