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Week 4 (Repeated Samples and Sampling the Distribution of X ̄ (Based on…

- - - - Bigger samples are less spread out in the distribution of means
      - They are normal distributions
    - - Population variance = σ2
      - Because there is extra uncertainty in that we estimated the variance, s2, the t distribution has slightly fatter tails than the normal distribution.
      - The confidence intervals are discovered through the equation
      - Here t α ,n−1 is the critical value we choose in the t distribution.
      - α reflects the coverage of the confidence interval
      - n − 1 is the the degrees of freedom
- - - - The result of a survey are only as good as the design of the questions
      - Avoid preambles that might swerve the sample a specific way
    - - We need to ensure that our sample is representative of the population. There are two types of bias associated with this.
        
        Selection Bias
        
        This arises when sampling leads to unrepresentative set of people being included
        
        Non-Response Bias
        
        Even is a random sample is taken, non response bias can be a problem. The people who are willing to cooperate and fill in the survey may tend to give different answers to those who refuse to participate.