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Data Analysis for Praxis I: Pre-Professional Skills Test Study Guide (page 2)

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Updated on Jul 5, 2011

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.

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