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Frequency Distribution
Shows how data are partitioned among several categories (or classes) by listing the categories/classes along with the number of data values in each of them. Ex: Daily commute times in LA
Frequency
The number of original values in a data class that fall into that class.
Lower class limits
The smallest numbers that can belong to each class
Upper class limits
The largest number that can belong to each of the classes.
Class boundaries
The numbers used to separate classes, but without the gaps created by class limits.
Class midpoints
The values in the middle of the classes, can be found by calculating the average of the lower class limit and the upper class limit.
Class width
The difference between two consecutive lower class limits in a frequency distribution. Calculated by max data value - min data value, divided by the number of classes.
What are the steps to manually create a frequency distribution?
Select the number of classes, usually between 5 and 20.
Calculate class width and round it up to a convenient number
Choose the first lower class limit by using either the minimum value or a convenient value below the minimum.
Using the first lower class limit and the class width, list the other lower class limits.
List the lower class limits in a vertical column, then determine the upper class limits.
Tally the data to determine the frequency distribution in each class
Relative frequency distribution or percentage frequency distribution
A frequency distribution where the frequency is represented with decimals, or percents
Cumulative frequency distribution
Gives the frequency of the class, plus all classes above it. Final frequency should match the total frequency.
Histogram
Graph consisting of bars of equal width drawn adjacent to each other. The horizontal scale represents classes of quantitative data values, and the vertical scale represents frequencies. The heights of the bars correspond to frequency values.
Dotplot
a graph of quantitative data in which each data value is plotted as a point (or dot) above a horizontal scale of values. Dots representing equal values are stacked.
Stemplot or Stem-and-leaf plot
represents quantitative data by separating each value into two parts: the stem (such as the leftmost digit) and the leaf (such as the rightmost digit).
Time-Series graph
A graph of quantitative data that have been collected at different points in time, such as monthly or yearly. Reveals information about trends over time.
Bar graph
Uses bars of equal width to show frequencies of categories of categorical (or qualitative data). Th bars may or may not be separated by small gaps.
Pareto chart
A bar graph for categorical data, with the added stipulation that the bars are arranged in descending order according to frequencies, so the bars decrease in height from left to right. Shows the relative distribution of categorical data so that it is easier to compare the different categories
Pie Chart
Graph that depicts categorical data as slices of a circle, in which the size of each slice is proportional to the relative frequency for the category.
Frequency Polygon
Depicts frequency distribution data that uses line segments connected to points located directly above class midpoint values.
Relative Frequency Polygon
Depicts relative frequency distribution data that uses line segments connected to points located directly above class midpoint values.
Center
A representative value that shows us where the middle of the data set is located.
Variation
A measure of the amount that the data values vary.
Distribution
The nature or shape of the spread of the data over the range of values (such as bell-shaped).
Outliers
sample values that lie very far away from the vast majority of the other sample values
Time
Any change in the characteristics of the data over time
