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