Sampling and Experimentation

Question 1: What are controlled and observational studies?

Answer 1: A controlled study, includes one or more treatment and control groups and attempts to examine the effects of one or more interventions on an outcome. The main emphasis of a controlled study is the implementation of an intervention.An observational study may or may not be a part of a controlled study. An observational study can examine random participant groups or intact groups (quasi-experimental). Observational studies focus on observation of different groups; this observation may occur after some intervention and thus serve as part of a controlled study, or it may occur separate from any type of experiment and/or randomization.

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Question 2: What are the two major characteristics of a well-designed and well-conducted survey?

Answer 2: The characteristics of a well-designed and well-conducted survey are the selection of sample units or clusters with probabilistic methods that can provide estimates of sampling error, and the absence of bias. A unit/participant is an element of the population (i.e., one person).A probabilistic method is consists of constructing a sample frame with a selection procedure and a data collection method. A sample frame may consist of the entire population or an identifiable subset of the population (i.e., names in a telephone directory, names from the DMV, social security numbers, electoral register). The sampling error is expressed as a confidence interval or a margin of error. For example, a 95 chance the mean is above the interval and a 2.5 A population in a survey is generally not homogeneous with respect to the observations being made; rather, it often consists of homogeneous subsets.

Question 3: Define the different types of surveys.

Answer 3: Different surveys vary in timing, sampling, mode of administration, and mode of data collection. The timing can be cross-sectional (data collected from sample units once), longitudinal (data collected from sample units at different intervals whose pattern is identical for each unit), and time-series (data collected from sample units at different intervals whose pattern may be different for each unit). The sampling may be simple random, stratified, systematic or clustered. In addition, sampling may be multi-stage, in which the sampling technique is repeated on increasingly smaller groups down to the sample unit. The mode of administration may be a researcher administered survey or a self-administered survey. The mode of data collection maybe telephone, mail, online, in-home, or mall intercept.

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