# chapter 2

Frequency

The number of values in a specific class of the distribution

Raw Data

Data collected in original form.

Frequency Distribution

The organization of raw data in table form, using classes and frequencies.

Pareto Chart

Used to represent a frequency distribution for a categorical variable, and the frequencies are displayed by the heights of the vertical bars, which are arranged in order from highest to lowest.

Pie Graph

A circle that is divided into sections or wedges according to the percentage of frequencies in each category of the distribution.

Time Series Graph

Represents data that occur over a specific period of time

Stem and Leaf Plot

A data plot that uses part of the data value as the stem and part of the data value as the leaf to form groups or classes.

Bar Graph

Represents the data by using vertical or horizontal bars whose heights or lengths represent the frequencies of the data.

Pareto Chart

Used to represent a frequency distribution for a categorical variable, and the frequencies are displayed by the heights of vertical bars, which are arranged in order from highest to lowest.

Lower Class Limit

the smallest data value that can be included in the class.

Upper Class Limit

The largest data value that can be included in the class.

Class Width

The distance between two sequential class limits. Found by subtracting the lower (or upper) class limit of one class from the lower (or upper) class limit of the next class.

Class Midpoint

The middle of the class. Found by adding the lower and upper class limits and dividing by 2, or adding the lower and upper class boundaries and dividing by 2.

Histogram

A graph that displays the data by using contiguous vertical bars of various heights to represent the frequencies of the classes.

Frequency Polygon

A graph that displays the data by using lines that connect points plotted for the frequencies at the midpoints of the classes. The frequencies are represented by the heights of the points.

Ogive (Cumulative Frequency Polygon

A graph that represents the cumulative frequencies for the classes in a frequency distribution.

Histogram

Graphed using the Class Boundaries and Frequencies. On the x-axis you will start with the lowest class boundary and end with the last upper class boundary. The frequency is graphed on the y-axis.

Xm

Class Midpoint

R

range

f

Frequency

Cf

Cumulative Frequency

n

Total Number of Frequencies

Sum (Greek letter sigma)

Data Presentation

When the data are qualitative or categorical, bar graphs can be used to represent the data. A bar graph can be drawn using either horizontal or vertical bars.

Range

The distance between the highest and lowest values in a data set. Found by subtracting the lowest value from the highest value.

positive slope

that there has been an increase from one time period to the next

negative slope

that there has been a decrease from one time period to the next

joint relative frequency

is the ration of the frequency in a particular category and the total number of data values

conditional relative frequency

numbers are the ratio of a joint relative frequency and related marginal relative frequency

marginal relative frequency

is the ratio of the sum of the joint relative frequency in a row or column and the total number of data values