Ch 3. Summarizing Univariate Data Using Graphs

What kinds of graphs can be created with qualitative data?

bar graph and pie chart

Bar graph

Contains horizontal/vertical bars whose heights and lengths represent data frequencies

Frequency distribution of a bar graph

table summarizes qualitative data and shows the frequency in each category

What type of data should you use bar graphs for?

use it for frequency, not for percentages

Pie chart

A circle divided into sections/categories according to the percent of frequencies in each category

What type of data should you use a pie chart for?

For relative frequency aka percentages

What kinds of graphs can be used to represent quantitative data?

Histogram, stem-and-leaf plot, box plt

Histogram

displays classes of data on a horizonal axis and frequencies of the classes on a vertical axis

Frequency distribution of histograms

organization of raw data in table form, using classes and frequencies, grouped into classes, each class has 2 values (class limits)

Lower class limit

Smallest value in the class

Upper class limit

The largest value in the class

Class width

The amount in between classes. Found by subtracting the upper/lower limit of one class from the upper/lower limit of the next class

Class midpoint

The average of the class limits. Take an average of the two values in the class.

Class boundaries

Numbers that are used to separate classes without creating gaps in the frequency distribution. Take an average of the adjacent upper class limits. Either add or subtract the class width to find the boundaries on the periphery of the table.

relative frequency

the ratio of the class frequency to the sum of all frequencies. (class/sum) = relative frequency

cumulative frequency distributiion

The sum of frequencies for that class and all previous classes. Frequency will get progressively larger.

Stem-and-leaf Plot

Uses part of data value as a stem and part of data value as a leaf

symmetric

both sides are mirror images

right skewed

cluster towards the lower end with a tail to the right

left skewed

cluster at the upper end with a tail to the left