Seven Common Graphs In Statistics (Page 3 of 3) in pdf

In our example of the elderly in the United States, let’s say we had 4 categories, each with it’s own color:

Less than 10% (red), 10 to 11.9% (yellow), 12 to 13.9% (blue), and 14% or more (green). If 12.2% of

Arizona’s population is over 65 years old, Arizona would be shaded blue on our map. Likewise, if Florida’s

has 15% of its population aged 65 and older, it would be shaded green on the map.

Maps can display geographical data on the level of cities, counties, city blocks, census tracts, countries,

states, or other units. This choice depends on the researcher’s topic and the questions they are exploring.

Histograms

A histogram is used to show the differences in frequencies or percentages among categories of an interval-

ratio variable. The categories are displayed as bars, with the width of the bar proportional to the width of the

category and the height proportional to the frequency or percentage of that category. The area that each bar

occupies on a histogram tells us the proportion of the population that falls into a given interval. A histogram

looks very similar to a bar chart, however in a histogram, the bars are touching and may not be of equal

width. In a bar chart, the space between the bars indicates that the categories are separate.

Whether a researcher creates a bar chart or a histogram depends on the type of data he or she is using.

Typically, bar charts are created with qualitative data (nominal or ordinal variables) while histograms are

created with quantitative data (interval-ratio variables).

Frequency Polygons

A frequency polygon is a graph showing the differences in frequencies or percentages among categories of

an interval-ratio variable. Points representing the frequencies of each category are placed above the

midpoint of the category and are joined by a straight line. A frequency polygon is similar to a histogram,

however instead of bars, a point is used to show the frequency and all the points are then connected with a

line.

Distortions In Graphs

When a graph is distorted, it can quickly deceive the reader into thinking something other than what the data

really says. Probably the most common way that graphs get distorted is when the distance along the vertical

or horizontal axis is altered in relation to the other axis. Axes can be stretched or shrunk to create any

desired result. For example, if you were to shrink the horizontal axis (X axis), it could make the slope of

your line graph appear steeper than it actually is, giving the impression that the results are more dramatic

than they are. Likewise, if you expanded the horizontal axis while keeping the vertical axis (Y axis) the

same, the slope of the line graph would be more gradual, making the results appear less significant than they

really are.

When creating and editing graphs, it is important to make sure the graphs do not get distorted. Oftentimes it

can happen by accident when editing the range of numbers in an axis, for example. Therefore it is important

to pay attention to how the data comes across in the graphs and make sure the results are being presented

accurately and appropriately so as to not deceive the readers.

Seven Common Graphs In Statistics Page 3