a part of the population from which we actually collect information, used to draw conclusions about entire population
sample selected by taking the members of the population that are easiest to reach, can produce unrepresentative data
voluntary response sample
consists of people who choose themselves by responding to a broad appeal. Voluntary response samples are biased because people with strong opinions are most likely to respond
simple random sample (SRS)
of size n, consists of individuals from the population chosen in such a way that every set of individuals has an equal chance to be in the sample actually selected
table of random digits
a long string of digits 0-9 with two properties
1. each entry in the table is equally likely to be any of the ten digits 0-9
2. the entries are independent of each other, that is knowledge of one part of the table gives no information about any other part
occurs when an individual chosen for the sample can't be contacted or refuses to participate
when the subject tells the interviewer what they want to hear rather than what actually happened to gain approval
observes individuals and measures variables of interest but does not attempt to influence responses. Purpose is to describe some group or situation.
deliberately imposes some treatment on individuals in order to observe their responses. Purpose is to study whether treatment causes a change in the response.
when two variables cannot be distinguished from one another when determining their effects on a response
randomized comparative experiment
an experiment that uses both comparison of two or more treatments and random assignment of subjects to treatment
control, randomize, enough subjects
basic principles of statistical design
1. _____the effects of lurking variables on the response, most simply by comparing two or more treatments
2. ______ to assign subjects to treatments
3. Use _______ in each group to reduce chance variation in results
experiment in which neither the subjects nor the people who interact with them know which treatment each subject is receiving.