Studied by 11 people
population
a group of individuals we want info about
census
collects data from every individual in the population
sample
subset of individuals selected from the larger population from which we collect data
sample survey
a study that collects data from a sample to learn about the population from which the sample was selected
bias
is shown if a study is likely to underestimate or overestimate the value you want to know
convenience sampling
selects individuals from the population who are easy to reach
voluntary response sampling
allows people to choose to be in the sample
random sampling
selects individuals using a chance process to determine which members of a population are included in the sample
single random sample (SRS)
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
sampling without replacement
an individual from a population can be selected only once
sampling with replacement
an individual from a population can be selected more than once
strata
groups of individuals in a population who share characteristics thought to be associated with the variables being measured in a study
stratified random sampling
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)
cluster
a group in the population that are near each other
cluster sampling (a type of convenience sampling)
selects a sample by randomly choosing clusters and including all members of the selected clusters in the sample (one section from each price point)
systematic random sampling
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
undercoverage bias
occurs when some members of the population are less likely to be chosen or cannot be chosen in a sample
response bias
when there is a systemic pattern of inaccurate answers to a survey question
nonresponse bias
when an individual chosen for the sample can't be contacted or refuses to participate
observational study
OBSERVES individuals and measures variables of interest but does not attempt to influence the responses
experiment
deliberately IMPOSES some treatment on individuals to measure their responses
explanatory variable
helps explain or predict changes in a response variable (what theyre DOING to the subject)
response variable
measures an outcome of a study (the EFFECT of what theyre doing)
confounding
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)
placebo
a treatment that has no active ingredient
placebo effect
when some subjects in an experiment respond favorably to an inactive treatment
treatment
a specific condition applied to the individuals in an experiment
experimental unit (EU)
the object the treatment is assigned (subjects when human)
factor
an explanatory variable that is manipulated and may cause a change in the response variable
levels
different values of a factor
control group
provides a baseline for comparing the effects of other treatments (often given a placebo)
single-blind
when EITHER the subjects or those who interact with them know which treatment a subject recieved
double-blind
when NEITHER subjects nor the people who interact with them know which treatment a subject recieved
comparison (part of CRCR)
comparing two treatments
random assignment (part of CRCR)
EU are assigned to treatments by CHANCE
control (part of CRCR)
keeping all other variables constant
replication (part of CRCR)
giving each treatment to enough EUs so that a difference in effects can be distinguished from chance variation
completely randomized design
when EUs are assigned to treatments at random
block
a group of experimental units that are known to be similar in some way that will affect results
randomized block design
the random assignment of treatments to EUs is carried out separately within each block
matched pair design
a design to compare 2 treatments using blocks with 2 EUs each.
type 1 of matched pair design
the two treatments are randomly assigned WITHIN the EUs
type 2 of matched pair design
each EU receives BOTH treatments in random order
sampling variability
refers to the fact that different random samples of the same size from the same population produce different samples
statistically significant
when the results are to unusual to be explained by chance (1-5%)
inference
can be made when samples are randomly selected
Note 
Flashcard (55)