Vocabulary of Statistics Part 3

Data Collection - Surveys Telephone pros: less costly, more candid cons: no phone, no call list Mailed questionnaire pros: cover more area, less cost cons: low response, inappropriate responses Personal Interview pros: in-depth responses, cons: training, cost, bias

Other methods of data collection Observation direct indirect surveying records

Four Methods of Sampling Random Systematic Stratified Cluster

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

Systematic Number each subject of the population, then select every nth subject. example: 600 kids at CHS. We want a sample of 100. 600 ÷ 100 = 6 Interview every 6th kid.

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.

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.

These are not the only methods convenience sampling - whatever is convenient to the researcher (Wal-mart) sequential double sampling multi-stage

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.

Experimental Study The researcher manipulates one of the variables and tries to determine how the manipulation influences other variables. teaching note: situps

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

Independent Variable The variable that is being manipulated aka: explanatory variable

Dependent Variable The resultant variable. aka: outcome variable.

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

Confounding Variable a variable that influences the dependent or outcome variable but cannot by separated from the independent variable.

Misuse of Statistics

3% of the students of Chatham High School want school uniforms. Which one is true?

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

Three out of four doctors recommend new Zimento

Suspect Samples How many doctors were actually used? 4? 40? 100? 10,000? How were they chosen?

What ‘ s the Problem Each of the following graphs is faulty!! Find the errors! Write some about the problem and how it can be fixed!

Misleading Graphs

51% agree 49% disagree

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?

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.

Detached Statistics Our brand of crackers has one-third fewer calories. compared to what? Zimento works four times faster. faster than what?

Implied connections Eating fish may help to reduce your cholesterol. Studies suggest that using Zimento will help you reduce your weight. Taking calcium will lower blood pressure in some people.