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A
population
is a collection of
units
of interest to us, a
variable
would be a
characteristic which could have different values for different units
Categorical or qualitative data—when the variable has no numeric content
Numerical or quantitative data—when the variable has numeric content.
Subtypes of numerical data:
a. discrete numeric variable—when the variable can assume only isolated
possible values—usually counts
b. continuous numeric variable—when the possible value of the variable fill
out a whole interval—for example physical measurements
Confounding variables
may exist. A confounding variable is a
hidden variable which is related to both of two variables which therefore turn out to be
related.
The purpose of random sampling is to assure that the sample is representative of the
population.
selection bias –in which some parts of the population are underrepresented
in the sample
Measurement bias—in which an instrument we use is faulty and introduces systematic
error into our data
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This note was uploaded on 04/29/2008 for the course MATH probstats taught by Professor Lukin during the Spring '08 term at Tulane.
 Spring '08
 Lukin

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