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Chapter 2: Summarizing and Graphing
Data
More Basic Terms
Raw data --- numbers and category labels that
are collected, but not yet processed
Variable --- a characteristic that differs from
one individual to the next
Observational unit (observation) --- single
individual who participates in a study
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Explanatory and Response Variables
Many questions are about the relationship
between two variables.
It is useful to identify one variable as the
independent variable (explanatory variable,
predictor, covariate) and the other variable as
the dependent variable (response variable).
Generally, the value of the independent variable
for an individual is thought to partially explain
the value of the dependent variable for that
individual.
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Describing Qualitative Data
Class---a category into which qualitative data can
be classified
Class frequency---number of observations in the
data set falling in a given class
Class relative frequency---class frequency
divided by the total number of observations in the
data set
class frequency
class relative frequency = n
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Describing Qualitative Data
Numerical summaries for one or two
categorical variables
Count how many fall into each category.
Calculate the percent in each category.
