Uses and Misuses of Statistics Chapter 1.5 Uses and Misuses of Statistics

Use vs. Misuse Describe data Compare two or more data sets Determine if a relationship exists between variables Test hypotheses Make estimates about population characteristics Sell products that don’t work properly Attempt to prove something true that is really not true Grab our attention by evoking fear, shock and outrage

Describing Misuse “There are three types of lies – lies, damn lies, and statistics” “Figures don’t lie, but liars figure”

Suspect Samples Using very small samples “three out of four dentists recommend Crest toothpaste” If only four dentists were surveyed, that could just be chance. The result could be quite different if 100 were surveyed

Volunteer Samples It is important to know how the subjects were selected Studies using volunteers have a built in bias because Particular socioeconomic background (unemployed) Spending time in another environment (college students and retirees) Generalizing results to both men and women Opinion polls that require phone or mailed response

Convenience Samples When intact groups are used for a sample, they may not be representative of the entire population (classroom) When all customers within a certain time frame are used for a sample, they may not be representative of the entire population (time)

Ambiguous Averages There are four commonly used terms that are loosely called averages. (mean, median, mode, and midrange) Depending on the data set, these can vary greatly

Changing the Subject Statistical distortion can occur when different values are used to represent the same data. For example, a politician might say “During my administration, expenditures increased a mere 3%” While someone running for the same position might say “during my opponent’s administration, expenditures increased a whopping $6,000,000”

Detached Statistics A claim that used detached statistics is one in which no comparison is made. For example, “our brand of crackers has one-third fewer calories”… than what?

Implied Connections Many claims attempt to imply connections between variables that may not actually exist. For example: “Eating fish may help to reduce your cholesterol” “Studies suggest that using our exercise machine will reduce your weight” “Taking calcium will lower blood pressure in some people”

Misleading Graphs

Faulty Survey Questions Survey questions can be phrased in ways the influence the way people answer them For example: a survey question like “Do you think the Union School District should build a new football stadium?” If it were phrased “Do you favor increasing school taxes so that the Union School District can build a new football stadium?”

So are statistics good? Yes, when used properly…. It’s like a car. If you use it to get to where you need to go, then it’s good. If you use it to run over people you don’t like, not so good…

Biased or Unbiased? Why? Eight citizens are asked their opinions about what trash should be collected. A phone-in survey is taken by a radio station to see how many listeners enjoy jazz in the morning. Every fortieth student who enters the school is asked to name their favorite sport. Ten students are randomly selected to participate in a survey about home computer usage.

Biased or Unbiased? Why? 5. Each math class randomly selects two students do represent their class on an advisory panel being assembled by the principal. 6. A shirt manufacturer wants to check quality control of their products. The plant manager decides to check every 5th shirt inspected by Inspector D. There are 15 inspectors in the plant. 7. A survey is conducted at the local shopping mall about household products used on a daily basis.

For example http://www.youtube.com/watch?v=FP6ZP0DM1po http://www.politifact.com/