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# Exam 3b - 1 In an observational study you are not giving...

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1. In an observational study you are not giving the subjects any type of treatment; you are just recording what you observe. In an experiment, you are giving the subjects a treatment and observing the effects of that treatment. 2. A retrospective study is an observational study in which you look at past data. Typically used when you are studying something that is unethical (such as drinking during pregnancy). A prospective study is an observational study in which you observe over a significant period of time. This is used when you want to study long term effects. 3. retrospective studies are usually unable to reach cause-and-effect conclusions. For example, we cannot conclude that physiotherapy definitively improves RTW outcomes among back-injured workers. This is because of confounding factors. 4. Considered the gold standard of study design, are prospective studies. They can provide evidence of cause-and-effect relationships and support changes in clinical practice or workplace interventions. In a randomized controlled trial, subjects are randomly assigned to receive the intervention or control treatment, and outcomes are evaluated after the intervention period. 5. Definitions a. Control: An experiment that isolates the effect of one variable on a system by holding constant all variables but the one under observation. b. Replicate: is the repetition of an experimental condition so that the variability associated with the phenomenon can be estimated. c. Randomize: is the process of making something random; this means: i. Generating a random permutation of a sequence (such as when shuffling cards). ii. Selecting a random sample of a population (important in statistical sampling). iii. Generating random numbers: see Random number generation. iv. Transforming a data stream (such as when using a scrambler in telecommunications). d. Block: is the arranging of experimental units in groups (blocks) that are similar to one another. For example, an experiment is designed to test a new drug on patients. There are two levels of the treatment, drug , and placebo , administered to male and female patients in a double blind trial. The sex of the patient is a blocking factor accounting for treatment variability between males and females .

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