simple random sample
individuals from a population are chosen so that each individual has an equal chance of being selected
systematic sample
members from a larger population are selected according to a random starting point but with a fixed, periodic interval
stratified random sample
members of the population are grouped then members from each group are randomly selected
cluster sample
members of the population are grouped then a set number of groups are randomly selected
bias
refers to the tendency of a process that tends to over- or under-estimate the value of a population parameter
convenience sampling
choosing individuals that are easiest to reach
voluntary response sampling
individuals choose themselves by responding to a survey or willingly participating in an experiment
undercoverage
occurs when some part of the population is not sampled at all or at a smaller proportion than seen in the population
nonresponse bias
occurs when some subjects won’t respond or participate
response bias
subjects may lie or mislead, intentionally or unintentionally
control
efforts made to minimize lurking variables
replication
the use of enough subjects to reduce chance variation
experiment
a treatment is deliberately imposed on individuals in order to observe their responses
observational study
individuals are observed and variables of interest are measured without any attempt to influence responses
treatment
a specific experimental condition applied to the subjects of an experiment
parameter
a numerical characteristic of a population
population
the entire pool from which a statistical sample is drawn
statistic
a numerical characteristic of a sample
sample
a small part or quantity intended to show what the whole is like
census
a sample that consists of the entire population
explanatory variable
variable that might help predict or explain changes in the response variable
response variable
the variable that measures the outcome of a statistical study
confounding variable
an extraneous variable that is associated with both the explanatory and response variables - makes it difficult to determine whether changes in the explanatory variable cause changes in the response.
experimental units
item or individual to which a treatment is assigned (sometimes called subjects),
placebo effect
describes that some subjects in an experiment will respond favorably to any treatment, even if it's inactive.
blinding
in an experiment, the subject does not know which treatment they are receiving
double blinding
neither the subjects nor those who interact with them and measure the responses know which treatment the subject is receiving
block design
the design of an experiment where the groups are known before the experiment that is in some way going to affect the results...block those groups together
matched-pairs design
common experimental design for comparing two treatments that uses blocks of size 2.
random sample
using a chance process to determine which members of a population are chosen for the sample.
random assignment
use of a chance process to assign experimental units to treatments - attempt to eliminate extraneous variables
prospective study
an observational study that selects observational units at a point in time and gathers data about them both at that time and into the future.
retrospective study
an observational study in which observational units are selected at a point in time and data about them gathered in the past.