Experiments

In an experiment, independent variables or factors are manipulated so that we can see the effect on dependent variables
The subjects that you use for your experiment are called experimental units

what makes a good experiment

• You need to control the effects of external influences or natural variability.
  • have a control group, a neutral group that receives no treatments, or only neutral treatments
  • A placebo is a neutral treatment, one that has no effect on the dependent variable.
  • If the group taking a placebo doesn’t know that it’s a placebo, then this is called blinding, and it’s called double blinding if even those administering the treatments don’t know
• You need to assign subjects to treatments at random.
• You need to replicate treatments
  Confounding occurs when the controls in an experiment don’t eliminate other possible causes for the effect on the dependent variable.

experiment design

• completely randomized design. For this, you literally assign treatments to subjects at random. Completely randomized design is similar to simple random sampling. Instead of choosing a sample at random, you assign treatments at random.
• randomized block design. For this, you divide the subjects into similar groups, or blocks. Randomized block design is similar to stratified random sampling. Instead of splitting your population into strata, you split your subjects into blocks.
• Matched pairs design is a special case of randomized block design. You can use it when there are only two treatment conditions and subjects can be grouped into like pairs.

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