Target Population Definition The complete collection of all individuals to be studied Examples All high school students in CA The population of Chula Vista College graduates

Sample Definition A subcollection of members selected from a population Examples 1000 randomly selected high school students 5000 citizens of Chula Vista randomly selected from the phone book Target population Sample

Statistical Significance Definition Something is statistically significant if it is unlikely to happen by chance Examples Flipping a coin 100 times and getting 95 heads is statistically significant because it is unlikely to occur by chance. It would seem to indicate that the coin is biased/weighted. Flipping a coin 100 times and getting 60 heads is less statistically significant

Biased Sample Definition A sample that misrepresents the target population (i.e., certain members are more likely than others to be included in the sample). A biased sample is a non-random sample. Example Target population: citizens of Chula Vista Sample: obtained by randomly polling people outside of the In ‘N Out

Voluntary Response Definition One type of biased sample where respondents themselves decide whether or not to be included; also called a self-selected sample. Example Online polls – the respondents are “self- selected,” so motivated and opinionated people are over-represented (Napster poll)

Biased Questions Definition Questions that are leading; they often hint at the “best answer” Examples With all the gang killings and domestic disputes ending with gunfire, do you think there should be legislation passed to hinder gun ownership? (6 agreed; 4 disagreed) The Second Amendment guarantees citizens the right to bear arms. Should this right be compromised by legislation in the 21 st century? (1 Yes; 9 No) (

Correlation (Association) Definition The values of one variable are somehow associated with the values of another variable Examples People with fancier cars tend to have big bank accounts, so there is a correlation between someone’s wealth and the price of the car they drive At many colleges, there is a correlation between student grades and evaluations of professors (which are completed by the students)

Causation (Causality) Definition A change in one variable causes a change in the other variable Note: It’s really hard to prove causality because of all the lurking variables! Examples Buying a fancy car will not cause you to have more money in the bank, even though those 2 things are correlated. Studies show that smoking and pulse rate are linked. Is there a causality?

HEALTH OF A PERSON COST OF THEIR CAR There is a correlation between how healthy a person is and how much his/her car costs… How much money do they have? Do they have a good job (with health insurance)? …but not necessarily a causality. Instead, there are several possible “lurking variables” which effect both a person’s health and the cost of their car!