Study design

Key concepts:

• Randomization
• treatment
• explanatory variable
• sample

Types of Studies

• Experiments are studies that involve manipulating a treatment that each participant receives
  • typically treatments are randomly assigned(see Randomization) to participants
  • we then measure participants’ response to the treatment
  • The treatment is the explanatory variable
  • establish a cause-and-effect relationship
  • We need to control everything(confounding) that could change the response, except for the treatments (randomization of treatments is the best way to accomplish this)
• Observational Studies are studies that do not involve manipulating the explanatory variables for participants.
  • we are simply ”observing” what is going on without intervening
  • nearly all surveys are observational studies

Sample

We want our sample to be representative of our population

• this means that our sample is nearly the same as our population, only smaller
• a representative sample allows us to generalize our results from the sample to the pop.
• biased: a sample that is not representative

Random Sample

We can choose people at random from our population to reduce the chances of getting a biased sample. Usually it is the best way to get a representative sample