Observations or cases form the rows; common attributes or variables form the
columns
•
Categorical Data
Also called qualitative or nominal variables
Identify group membership
•
Numerical Data
Also called quantitative or continuous variables
Describe numerical properties of cases
Have measurement units
Size of bike (cm)
and
Amount spent ($)
are examples
•
Measurement Scales
Nominal – name categories without implying order (categorical). E.g. gender.
Ordinal – name categories that can be ordered (categorical). E.g. the good, the
bad and the ugly.
Interval – numerical values that can be added or subtracted (arbitrary
zero).E.g. temperature.
Ratio – numerical values that can be added, subtracted, multiplied or divided
(makes ratio comparisons possible, zero is not arbitrary). E.g. height.
Likert Scale (Ordinal – 5 to 7 Categories)
Recode:
building a new variable from another (recoding price into expensive
or inexpensive)
Aggregate:
reduce rows in a data table by counting or summing values within
categories
Time series – data recorded over time
Timeplot – graph of a time series showing values in chronological order
Frequency – regular time spacing of data in a time series (e.g., daily, monthly,
etc.)
Crosssectional – data observed at the same time
The distribution of a categorical variable is a list of values with its associated
count (frequency)
A frequency table summarizes the distribution of a categorical variable
A relative frequency table shows the proportion (or percentage) in each
category
Bar Chart
Uses horizontal or vertical bars to show the distribution of a categorical
variable
Is called a Pareto chart when the categories are sorted by frequency (popular
in quality control)
Becomes cluttered with too many categories
Is appropriate for ordinal categorical variables
The Pie Chart
Uses wedges of a circle to show the distribution of a categorical variable
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Commonly chosen to illustrate market shares or sources of revenue for a
company
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 Fall '07
 Cummings
 Normal Distribution, Standard Deviation, Variance, Probability theory

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