Organizing and Graphing
Quantitative Data
Sections 2.3 – 2.4
Frequency Distribution for
Quantitative Data
Frequency Distribution for
Quantitative Data
• Lists all the classes (intervals) and the # of
values in each class (frequency).
• Class Boundary – midpoint between
upper limit of one class and lower limit of
next class.
• Class width = upper boundary – lower
boundary.
• Class Midpoint = lower limit + upper limit
2
Example:
Constructing Frequency
Distribution Tables
• Number of classes - usually 5-20.
• Class width.
– To approximate class width:
Largest value – smallest value
Number of classes
Example: Start with Data
Frequency Distribution of Data
Relative Frequency Distribution
Histograms
• Classes on x-axis, frequencies/relative
frequencies/percentages on y-axis.
Truncation
Relative Frequency Histogram
Polygon
• Graph formed by joining midpoints of bars.
Frequency Distribution Curve
• As the # of data and classes increase the
polygon becomes more of a smooth curve.
Shapes of Histograms
• Symmetric
Shapes of Histograms
• Skewed
Shapes of Histograms
• Uniform