# AP Statistics : How to identify sources of bias in an experiment

## Example Questions

### Example Question #294 : Ap Statistics

What type of sample was used in the following scenario:

Brad wants to know about the shopping habits of teenagers. He goes to the local mall and everytime he sees a teenager he asks them to fill out his survey. He spends one hour collecting responses on the top floor of the mall and one hour collecting responese on the bottom floor of the mall.

Stratified random sample

Convenience Sampe

Cluster sample

Multistage sample

Simple random sample

Convenience Sampe

Explanation:

The correct anwer is a convenience sample because the sample is drawn from a population that is close, readily available, and convenient. The sample does not represent the shopping behaviors of all teenagers.

### Example Question #295 : Ap Statistics

Which of the following experiments has the least amount of bias?

A randomized double-blind experiment in which there are two experimental groups: Group A receiving a small dose of a particular drug and Group B receiving a large dose of a particular drug.

None of these examples contain any potential bias.

A survey of the number of people that watch online TV conducted using email.

A randomized double-blind experiment in which test subjects are assigned to either a placebo or a therapeutic agent that is used to improve metabolism.

A survey of how many people enjoy shopping conducted at a shopping mall.

A randomized double-blind experiment in which test subjects are assigned to either a placebo or a therapeutic agent that is used to improve metabolism.

Explanation:

The correct answer contains a control group and experimental group (placebo vs. therapeutic agent). Furthermore, it is randomized and double-blind.

The other incorrect choices introduce some form of bias - primarily selection bias in the two examples of surveys. The last example (the experiment with two experimental groups) does not have a control variable or placebo.

### Example Question #296 : Ap Statistics

A major chocolate company wants to test the effects of adding more sugar to their standard chocolate bar to see if customers enjoy it more.

They select 10 subjects to randomly participate in a taste test. They bring in samples of their original product, which is sold in tiny squares that says the company's name on them, and samples of the increased-sugar versions, which are plain chocolate squares of the same size. The company asked participants to taste both chocolates and rank how much they like them on a scale of 1 to 10.

Which of the following represents a possible source of bias in the study?

The original recipe has the company's name on it, but the new sample does not.

People may not all like chocolate to the same degree.

Some people may wish they were eating a different dessert.

There are not many taste-testers who are qualified to evalutate food.

There is no bias.