STAT 110 – Chapter 1 Definitions individuals – the objects described by a set of data variable – any characteristic of an individual observational study – observes individuals and measures variables of interest but does not attempt to influence the responses Æ the purpose of this type of study is to describe some group or situation sample survey – a type of observational survey in which a sample is selected and asked to respond to questions population – the entire group of individuals about which we want information sample – a part of the population from which we actually collect information, used to draw conclusions about the wholecensus – a sample survey that attempts to include the entire population in the sample experiments – deliberately imposes some treatment on individuals in order to observe their responses Æ the purpose of an experiment is to study whether the treatment causes a change in the response Chapter 2 Definitions biased – systematically favors certain outcomes convenience sampling – selection of whichever individuals are easiest to reach voluntary response sample – chooses itself by responding to a general appeal simple random sample 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
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