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Collecting Data

Collecting Data. Observational Study. In an observational study researchers don’t assign choices, they simply observe them. Observational studies are valuable for discovering trends and possible relationships .

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Collecting Data

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  1. Collecting Data

  2. Observational Study • In an observational study researchers don’t assign choices, they simply observe them. • Observational studies are valuable for discovering trends and possible relationships. • However, it is not possible for observational studies to demonstrate a causal relationship.

  3. Experiment • An experiment is a study that allows you to prove cause-and-effect relationship. • They manipulate factor levels to create treatments. • They randomly assign subjects to these treatment levels. • They compare the responses of the subject groups across treatment levels.

  4. Experiment • An experiment must have at least one explanatory variable, called a factor, to manipulate, and at least one response variable to measure. • A treatment is a combination of specific levels from all the factors that a subject receives.

  5. The 3 Principles of Experimental Design • Control to make sure all conditions are as similar as possible for all treatment groups. • Randomize to equalize the effects of unknown or uncontrollable sources of variation. No experiment is valid without randomization. • Replicate and apple the treatments to a number of subjects.

  6. Control • A group who receive no treatment is called the control group. • This gives a baseline to compare treatment groups. • To further control unseen variables, subjects in both the control and treatment groups are not allowed to know which group they are in. This is called blinding.

  7. Blinding • You may have heard of a placebo effect. • This is when people think they are getting a treatment and claim to have a change. • To control this, a placebo is used in an experiment. • This is a false treatment. Usually this is a fake pill. It is the easiest way to blind a subject.

  8. Blinding • When those receiving the false treatment or those doing the evaluating do not know who received what treatment we call it single-blind. • When both those receiving the treatment and those doing the evaluating are unaware of who received each treatment is called double-blind.

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