Data Analysis for Praxis I: Pre-Professional Skills Test Study Guide

Bar Graphs

Whereas scatter plots are used to show change, bar graphs are often used to indicate an amount or level of occurrence of a phenomenon for different categories. Consider the following bar graph. It illustrates the number of employees who were absent due to illness during a particular week in two different age groups.

In this bar graph, the categories are the days of the week, and the frequency represents the number of employees who are sick. It can be immediately seen that younger employees are sick before and after the weekend. There is also an inconsistent trend for the younger employees with data ranging all over the place. During mid-week the older crowd tends to stay home more often.

How many people on average are sick in the 41–65 age group? To find the average, you first must find out how many illnesses occur each week in the particular age group. There are 41 illnesses in total for a five-day period (3 + 10 + 12 + 12 + 4 = 41). To calculate the average, just divide the total illnesses by the number of days for a total of 8.2 illnesses or, more realistically, 8 absences per day.

Pictographs

Pictographs are very similar to bar graphs, but instead of bars indicating frequency, small icons are assigned a key value indicating frequency.

In this pictograph, the key indicates that every icon represents 10 people, so it is easy to determine that there were 12 × 10 = 120 freshmen, 5.5 × 10 = 55 sophomores, 5 × 10 = 50 juniors, and 3 × 10 = 30 seniors.

Pie Charts and Circle Graphs

Pie charts and circle graphs are often used to show what percent of a total is taken up by different components of that whole. This type of graph is representative of a whole and is usually divided into percentages. Each section of the chart represents a portion of the whole, and all of these sections added together will equal 100% of the whole. The following chart shows the three styles of model homes in a new development and what percentage of each there is.

The chart shows the different models of homes. The categories add up to 100% (25 + 30 + 45 = 100). To find the percentage of Estate homes, you can look at the pie chart and see that 45% of the homes are done in the Estate model.

Broken Line Graphs

Broken line graphs illustrate a measurable change over time. If a line is slanted up, it represents an increase, whereas a line sloping down represents a decrease. A flat line indicates no change.

In the broken line graph below, the number of delinquent payments is charted for the first quarter of the year. Each week the number of outstanding bills is summed and recorded.

There is an increase in delinquency for the first two weeks and then the level is maintained for an additional two weeks. There is a steep decrease after week 5 (initially) until the ninth week, where it levels off again but this time at 0. The 11th week shows a radical increase followed by a little jump up at week 12, and then a decrease to week 13. It is also interesting to see that the first and last weeks have identical values.

This diagram shows a sequence of events to construct two new objects out of one pipe and a few other parts. First, the instructions show that the pipe must be cut into two pieces with a saw. The next two levels show how the assembly will take place, first adding the end pieces and then bolting in those pieces.

Diagrams could be used to show a sequence of events, a process, an idea, or the relationship between different events or people.

When you see a diagram, first ask what the purpose of it is. What is it trying to illustrate? Then look at the different labeled parts of the diagram. What is the function of each part? How are they interrelated? Take a look at the following diagram:

This diagram is a typical chart of how to start a new project. It starts (on the left), by learning about the assignment from the manager and then investigating several aspects of heading a project, including the client, resources, and budget. Once an overall picture is achieved you will then know how many people will be required for the project in order to create an accurate schedule for the project. There are also reminders and further protocols within the diagram in the links.

Now, take the skills you have learned or honed in this review and apply them to the next practice test.