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