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

“There are three types of lies – lies, damn lies,

and statistics”

“Figures don’t lie, but liars figure”

Describing Misuse

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

Suspect Samples

It is important to know how the subjects were

selected Studies using volunteers have a built in bias

because1. Particular socioeconomic background

(unemployed)2. Spending time in another environment

(college students and retirees)3. Generalizing results to both men and women4. Opinion polls that require phone or mailed

response

Volunteer 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)

Convenience Samples

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

Ambiguous Averages

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”

Changing the Subject

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?

Detached Statistics

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”

Implied Connections

Misleading Graphs

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?”

Faulty Survey Questions

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…

So are statistics good?

http://

www.youtube.com/watch?v=FP6ZP0DM1po

http://www.politifact.com/

For example