ch 4

a group of individuals we want info about

collects data from every individual in the population

subset of individuals selected from the larger population from which we collect data

a study that collects data from a sample to learn about the population from which the sample was selected

is shown if a study is likely to underestimate or overestimate the value you want to know

selects individuals from the population who are easy to reach

allows people to choose to be in the sample

selects individuals using a chance process to determine which members of a population are included in the sample

a sample of size N is chosen in a way that every group of N individuals in the population has an equal chance to be in the sample

an individual from a population can be selected only once

an individual from a population can be selected more than once

groups of individuals in a population who share characteristics thought to be associated with the variables being measured in a study

selects a sample by choosing a single random sample (SRS) from each stratum (groups of similar people) and combining the SRSs into one overall sample (a ring around the stadium)

a group in the population that are near each other

selects a sample by randomly choosing clusters and including all members of the selected clusters in the sample (one section from each price point)

selects a sample from an ordered arrangement of the population by randomly selecting one of the first K individuals and choosing every Kth individual thereafter

occurs when some members of the population are less likely to be chosen or cannot be chosen in a sample

when there is a systemic pattern of inaccurate answers to a survey question

when an individual chosen for the sample can't be contacted or refuses to participate

OBSERVES individuals and measures variables of interest but does not attempt to influence the responses

deliberately IMPOSES some treatment on individuals to measure their responses

helps explain or predict changes in a response variable (what theyre DOING to the subject)

measures an outcome of a study (the EFFECT of what theyre doing)

occurs when two variables are associated in such a way that their effects on a response variable cannot be distinguished from each other (too similar)

a treatment that has no active ingredient

when some subjects in an experiment respond favorably to an inactive treatment

a specific condition applied to the individuals in an experiment

the object the treatment is assigned (subjects when human)

an explanatory variable that is manipulated and may cause a change in the response variable

different values of a factor

provides a baseline for comparing the effects of other treatments (often given a placebo)

when EITHER the subjects or those who interact with them know which treatment a subject recieved

when NEITHER subjects nor the people who interact with them know which treatment a subject recieved

comparing two treatments

EU are assigned to treatments by CHANCE

keeping all other variables constant

giving each treatment to enough EUs so that a difference in effects can be distinguished from chance variation

when EUs are assigned to treatments at random

a group of experimental units that are known to be similar in some way that will affect results

the random assignment of treatments to EUs is carried out separately within each block

a design to compare 2 treatments using blocks with 2 EUs each.

the two treatments are randomly assigned WITHIN the EUs

each EU receives BOTH treatments in random order

refers to the fact that different random samples of the same size from the same population produce different samples

when the results are to unusual to be explained by chance (1-5%)

can be made when samples are randomly selected