Chapter 7

sample

a collection of people or objects taken from the population of interest

population

a group of objects or people we wish to study

biased

a method is _____ if it has a tendency to produce an untrue value

statistic

a numerical characteristic of a sample

parameter

a numerical value that characterizes some aspect of a population

census

a survey in which every member of the population is measured

estimator

another name for statistic; the numbers that result are called estimates

confidence interval

gives a range of plausible values for our population parameter and a confidence level

precision

reflected in the spread of the sampling distribution and measured by using the standard deviation of the sampling distribution

sampling bias

taking a sample that is not representative of the population

margin of error

the amount, plus and minus, to the estimate; tells how far from the population value our estimate is

statistical inference

the art and science of drawing conclusions about a population on the basis of observing only a small subset of that population

voluntary-response bias

when the only people who respond to a poll are those who have strong feelings about the result

sampling distribution

the probability distribution of the sample proportion (p-hat)

Central Limit Theorem

CLT 1. random and independent 2. large sample (at least 10 successes and 10 failures) 3. big population (sample must be 10 times bigger than the sample size)

standard error

SE; the standard deviation of the sampling distribution

simple random sampling

SRS, draw subjects from the population at random and without replacement

measurement bias

comes from asking questions that do not produce a true answer

confidence level

expresses our level of confidence in the confidence interval

bias

measured as the distance between the mean value of the estimator (the center of the sampling distribution) and the population parameter

convenience sample

not a random sample; a sample that was collected conveniently

nonresponse bias

occurs when people selected to participate in the survey refuse to do so

without replacement

once a subject is selected for a sample, that subject cannot be selected again