Alg 2/Trig Honors – Stats Unit Day 8 Statistical Studies Alg 2/Trig Honors – Stats Unit Day 8

Surveys Surveys are relatively easy to conduct, provide quick results, and can often provide interesting/captivating media headlines. Keys to using a survey for collecting data: Quality of Questions Selecting Participants

Quality of Survey Questions Quality of Survey Questions – Loaded questions, leading questions, confusing questions Sample Survey Question: “Do you like the cafeteria’s food?” Versus “For each of the following items offered by our cafeteria, identify whether you:” a. Like the Item b. Do NOT like the Item c. Have never tried the Item

Quality of Survey Questions “Don’t you think that a small increase in property taxes is a worthwhile investment for improving the quality of education for our children?” Versus “Our town is considering a 4% increase in property taxes to raise funds for a new school to be built. What is your opinion on the proposed increase in property taxes? 1 2 3 4 5 Strongly in favor In favor Neutral Oppose Strongly oppose

Selecting Participants  How are participants selected? Random, Convenience, Volunteers, Compensated 1936 Election - Alf Landon versus Franklin D. Roosevelt – Literary Digest Poll versus George Gallup Ideally, survey results are used to generalize about the larger population. To do requires sampling a large enough portion of the population and doing so in an appropriate way

Observational Studies Observational Studies do not attempt to impose a treatment or influence the responses of those being studied (A survey is really one type of observational study)    Sample Observational Study Researches investigate the link between hours of sleep the night before an exam and performance on the exam

Observational Studies - Correlation The main disadvantage of an observational study is that a cause-and-effect conclusion cannot be drawn from any observed relationship.   Correlation does not imply causation! Correlation Examples: There is a positive correlation between ice cream sales and drowning accidents There is a positive correlation between the number of books in a home and the earnings potential of a child http://www.businessinsider.com/number-of-books-in-home-impacts-childs-future-2016-7 There is a positive correlation between the number of people killed by venomous spiders in a year and the number of letters in the winning word of the National Spelling Bee Spurious Correlations - http://tylervigen.com/spurious-correlations

Experiments An experiment imposes a treatment to see how it impacts the response. If an experiment is well-designed and conducted, experiments enable a cause and effect conclusion to be made.    Designing a good experiment: Include a large enough sample size Choose subjects that accurately represent the target population Assign subjects randomly to the treatment and control groups Controls for possible confounding/lurking variables Is ethical