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Unit Three (Observational Studies and Experiments (Vocabulary…

- - - - Convenience Sampling
        
        When you only sample people who are convenient to you. Example includes sampling people only at the library because you are at the library.
      - Voluntary Response Sampling
        
        This is when people choose themselves by responding to a general appeal. They show bias because usually people with strong opinions are most likely to answer. An example is an online internet poll, where people choose to answer.
      - Undercoverage
        
        This occurs when some groups in the population are left out of the process of choosing the sample. An example of this is a survey within households, which excluded homeless people.
  - - - Wording Bias
        
        The wording of questions is important. Confusing or leading questions can introduce strong bias, and changes in wording can greatly change a survey's outcome. An example of this is when asked if all illegal immigrants should be deported or if illegal immigrants who have worked in the US should be deported. The responses to this would be different. Also would be an example of bias.
      - Response Bias
        
        A systematic pattern of incorrect responses in a sample survey leads to response bias. An example of this is when asked the question: Have you visited the dentist in the last 6 months?, and the answer could be "Yes", even though they went 8 months ago.
      - Non-response
        
        This occurs when an individual chosen for the sample can't be contacted or refuses to participate. An example of this is when a student who was chosen to take a survey did not take the survey.
  - - - Example could be asking people what their favorite country is depending on what country that person is from or lives in.
      - Direction: Biases can operate in different directions. They can lead to an overestimation or an underestimation of the true answer.
  - - - Advantages: Tends to reduce sampling error. Includes an even amount of people from different backgrounds.
        Disadvantages: More cost and usually a smaller sample can be taken with this.
  - - - Advantages: Can allow a larger sample to be obtained at a lower cost and less time. Disadvantages: Increases sampling error because there could be many people taken from a survey from the same background, unlike a stratified survey.
- - - - Example: Find 100 women ages 25-35 who have been eating fish weekly and who are planning on becoming pregnant see if this has any effect on their babies.
  - - - Example: Find 100 women who do not eat fish. Assign 50 of them to a category of eating fish weekly and the rest to not eating fish at all and see the effects this has on their babies.
  - - - A lurking variable can lad to confounding because there is a third variable that explains why two variables are related or unrelated. This variable is not taken into account, leading to confounding. An example can be that the sales of Bruins tickets and snow shovels decline together. This can be explained by the fact that Bruins tickets and snow shovels will be purchased more in the winter.
  - - - Is the physical entity that can be assigned.
    - - Is an explanatory variable manipulated by the experimenter, also called an independent variable. Each factor can have levels, or different values of the factor.
    - - Combinations of factor levels.
    - - This is how the experiment is measured.
  - - - This will help to decrease experimental error.
    - - Ensures that the experiment is statistically valid. You need to have the subjects or experimental items randomly assigned.
    - - This allows comparison in the experiment from something that is known.