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Vocabulary of Statistics Part 3
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Data Collection - Surveys Telephone pros: less costly, more candid pros: less costly, more candid cons: no phone, no call list cons: no phone, no call list Mailed questionnaire pros: cover more area, less cost pros: cover more area, less cost cons: low response, inappropriate responses cons: low response, inappropriate responses Personal Interview pros: in-depth responses, pros: in-depth responses, cons: training, cost, bias cons: training, cost, bias
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Other methods of data collection Observation direct indirect indirect surveying records
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Four Methods of Sampling Random Systematic Stratified Cluster
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Random selected by using chance methods or random numbers put everybody’s name in a bucket and choose assign a number, use a random number generator
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Systematic Number each subject of the population, then select every nth subject. example: 1600 kids at MHS. We want a sample of 200. 1600 ÷ 200 = 8 Interview every 8 th kid.
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Stratified Divide the population into groups (called strata) according to some characteristic that is important to the study. example: you might want to only survey juniors.
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Cluster Use an entire, intact, group. example: every person who lives in a certain apartment building. example: every person in Mrs. Peddy’s third period class.
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These are not the only methods convenience sampling - whatever is convenient to the researcher (Wal-mart) sequential double sampling multi-stage
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Observational Studies The researcher merely observes what is happening or what has happened in the past and tries to draw conclusions based on these observations.
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Experimental Study The researcher manipulates one of the variables and tries to determine how the manipulation influences other variables. teaching note: situps
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In a true experimental study, subjects should be assigned randomly when random assignment is not possible (i.e. existing classrooms), the study is said to be quasi- experimental
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Independent Variable The variable that is being manipulated aka: explanatory variable
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Dependent Variable The resultant variable. aka: outcome variable.
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When doing an experiment you generally need two groups: treatment group: the one you are experimenting on control group: the one you are doing nothing to but observing
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Confounding Variable a variable that influences the dependent or outcome variable but cannot by separated from the independent variable.
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Misuse of Statistics
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3% of the students of Muskogee High School want school uniforms. 64% of the students of Muskogee High School want school uniforms. Which one is true?
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The pure and simple truth is rarely pure and never simple Oscar Wilde First get your facts; then you can distort them at your leisure Mark Twain There are three kinds of lies: lies, damn lies, and statistics Benjamin Disraeli
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Three out of four doctors recommend new Zimento
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Suspect Samples How many doctors were actually used? 4? 40? 100? 10,000? How were they chosen?
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Misleading Graphs
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51% agree 49% disagree
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Misleading wording in surveys Do you support bringing freedom and democracy to the people of Iraq? Do you support the unprovoked military action of the U.S. taking place in Iraq?
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Changing values to represent the same data The incumbent states, “During my tenure expenditures have only risen 1%.” The challenger states, “During my opponents tenure expenditures have risen $10,000,000.” Both statements are true, but one uses percentage and the other dollar amounts.
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Detached Statistics Our brand of crackers has one-third fewer calories. compared to what? Zimento works four times faster. faster than what?
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Implied connections EEEEating fish may help to reduce your cholesterol. SSSStudies suggest that using Zimento will help you reduce your weight. TTTTaking calcium will lower blood pressure in some people.
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Assignment Page 26 1 - 29
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