Unit 3 AP Stats Review

a procedure by which EVERY MEMBER of a population is selected for study

a sample w/ the essential characteristics of the population studied without any bias

list of all the members of population from which we can draw a sample

a sample in which every individual in the population has a known probability of being sampled

a sample in which ALL samples of size x have an equal probability of being drawn

a sample in which the starting point is chosen randomly, but afterwards the sample is drawn from some predetermined system/pattern (e.g. every 12th person)

sampling frame is divided into homogeneous groups, then random sample is drawn from each homogeneous group

sampling frame is divided into groups which are all the same/intended to be representative of the population; then, clusters are sampled randomly

a sample in which people choose whether or not to participate in the survey/respond (TENDS TO BE BIASED, VOLUNTARY RESPONSE BIAS)

sample drawn however is most convenient (TENDS TO BE BIASED)

individuals are selected intentionally to try to reflect different quotas of groups in the population, e.g. selecting x amount of teens to include because teens make up y proportion of the population (TENDS TO BE BIASED)

the tendency of a sample statistic to systematically over- or under-estimate a population parameter (e.g. our sampling method will regularly & systematically produce samples that misrepresent our data in the same way)

one part of the population being sampled is excluded/underrepresented

certain individuals (those who feel certain ways about the subject matter of the survey) will choose not to respond/to respond; the groups of individuals who respond/don’t respond are the same w/ respect to the variable of interest & thus we’ve under/overrepresented a group in our population

bias which occurs when the wording of the question(s) being asked influences the responses in a SYSTEMATIC way

the respondent might not want to give a truthful answer to the question (e.g. income questions); the respondent might not UNDERSTAND the question (ambiguous wording); the respondent might want to please the interviewer; the order in which options were listed might influence the answers of the respondent; etc.

this difference is too large to attribute to chance/natural random variation

a study in which researchers ASSIGN individuals to treatments/impose treatments on individuals

a study in which researchers observe individuals and record data but DON’T impose treatments

past; future

a variable that has an effect on the outcomes of the study but whose effects can’t be separated from those of the treatment variable

a situation in which all variables other than the one of interest are HELD CONSTANT across all treatment groups

randomization, replication, and control

equalize groups so that the effects of extraneous variables are equally distributed among groups

minimize effects of random chance on our results (e.g. ensure differences between results for our groups aren’t due to random extremity)

minimize confounding; ensure groups only differ with respect to variable of interest

subjects randomly assigned to treatment groups, treated; effects of treatments compared

an inactive treatment used when effects of treatment are compared to effects of no treatment (placebo only used for HUMAN subjects)

preventing a party in the experiment from knowing which treatment they received (single blind: either subject or evaluator doesn’t know; double blind: both subject and evaluator don’t know)

specify method of randomization, specify whether sampling w/ or w/out replacement, and (if using random digits table) specify what represents 1 [e.g. 01 is 1]

completely randomized experiment is performed WITHIN each block, results compared WITHIN blocks

two subjects similar to each other are paired, becoming a block, or one person becomes a pair & their before/after results are compared