INFO 370 - L07 - October 20, 2004
Notes by: Aaron, Yaptinchay, Sean, Prins

Tomorrow's lab to start @ 5PM
Google Talk in EE105 

Mean greater than median on a positive skew
Median greater than the mean on a negative skew

Central Limit Theorem:
    > Various distributions and means were taken from samples
    > 70-80 observations gives you a pretty good estimate of the mean
    

// Begin Slides
Generalization
    > Sample generalization: form a sample to the whole population
        ex. using info students to generalize UW students
    > Cross-population generalization: from one population to another
        ex. using UW students to generalize other university students

Evaluating Sampling Quality
    > How clearly was the population defined?
    > What methods were used to select the sample?
    > Do the cases selected represent the population from which they were selected?
    > Is cross-population generalization valid?

Factors Acting Against Quality
    > The sampling frame is incomplete
        - ex.: "Dewey defeats Truman" newspaper flop
        - people may have been left out
        - cell phone users nowadays
    > Low participation rate
        - self-selection bias
        - make sure your questions aren't too probing, personal, turns off and stops answering question
        - once subjects gets past 50% of the survey, momentum makes them finish and they are more willing to answer tougher questions
    > Unwarranted cross-population generalizations
        - include all socio-economical biases

Sample Size
    Factors determining the selection of size:
    > The degree of confidence required
    > The homogeneity of the population (they all respond in a similiar fashion)
    > The complexity of data analysis

Conclusion
    > Selecting units in such a way that what we learn about the sample holds true for the population
    > Sampling method determines the degree of generalizability


                        Random Samples *CHECK*
                        Non-random samples *X*
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