Unit 1B Statistics Vocabulary

voluntary response sample

consists of people who choose themselves by responding to a general appeal

confounding variable

in an observational study provides an alternative explanation for the observed relationship between the explanatory and response variable determined in the study, thereby reducing the possibility of concluding a causal relationship between the explanatory and response variables of interest

statistical inference

provides ways to answer specific questions from data with some guarantee that the answers are good ones

population

the entire group of individuals that we want information about

sample

a part of the population that we actually examine in order to gather information

convenience sampling

chooses individuals easiest to reach

simple random sample (SRS)

of size n consists of n individuals from the population chosen in such a way that every set of n individuals has an equal chance to be the sample actually selected

design

[of a sample] refers to the method used to choose the sample from the population

bias

the design of a study that systematically favors certain outcomes

probability sample

gives each member of the population a known chance (greater than zero) to be selected

strata

the division of the population into groups of similar individuals

strata sample

to sample important groups within the population separately, then combine the samples

strata random sample

to choose a separate SRS in each stratum and combine these SRSs to form the full sample

multistage sample design

select successively smaller groups within the population in stages; each stage may employ an SRS, a stratified sample, or another type of sample

undercoverage

occurs when some groups in the population are left out of the process of choosing the sample

nonresponse

occurs when an individual chosen for the sample cannot be contacted or refuses to cooperate

wording of question

the most influence on the answers given to a survey

sampling frame

the list of individuals from which a sample is actually selected

observational study

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

experiment

a study in which a researcher assigns conditions, or treatments, to experimental units to explore an investigative question of interest about the population

experimental units

the individuals on which the experiment is done

subjects

when the experimental units are humand beings

treatment

a specific experiment condition applied to the units

factors

the explanatory variables in an experiment

placebo

a dummy treatment that can have no physical effect

control group

the group of patients who received the placebo treatement

randomization

the use of chance to divide experimental units into groups

completely randomized design (CRD)

all the experimental units are allocated at random among all the treatments

statistically significant

an observed effect too large to attribute plausibly to chance

probability model

a model used to calculate a theoretical answer

simulation

the imitation of chance behavior, based on model that accurately relfects the experiment under consideration

replication

repeat each treatment on large enough number of experimental units or subjects to allow the systematic effects of the treatments to be seen

double blind experiment

neither the subjects nor the people who have contact with them know which treatment a subject received

lack of realism

the subjects or treatments or setting of an experiment may not realistically duplicate the conditions we really want to study

block

a group of experimental units or subjects that are similar in ways that are expected to affect the response to the treatments

block design

the random assignment of units to treatments is carried out seperately within each block

match pairs design

a common form of blocking for comparing two treatments

survey

an observational study in which the data are collected from humans using a standard set of questions

response variable

an outcome measured on each experimental unit after the treatment has been administered

census

consists of recording information from all items or individuals in a population