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.