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Test PrepACTScienceData Representation

ACT Science Skill Review: Data Representation

Most Science tests will include three Data Representation passages. Thankfully, these are usually shorter than any of the other types. Still, to be successful on these, you must be able to interpret the data and, before you can do that, you must first determine what is being represented. Once you understand that, you must determine what the depicted values mean. Are there any units of measurement? If there are more than one, how does one unit of measurement relate to another? Finally, you must look for trends in the data.

Data Representation passages can be broken down into further subgroups:

Graphs and Charts

There are many types of graphs and charts. They have actual values and units of measurement for precise and direct interpretation. The key to understanding these figures is determining what the variables (the “things” that are changing) are. There are two kinds of variables: independent (not affected by other factors or variables) and dependent (affected by other factors or variables). The dependent variables are often represented in some relation to one another. This is where you must observe the trends (how one variable relates to another). One of the most valuable uses for graphs is to “predict” data that are not measured on the graph. This happens in one of two ways:

  • Extrapolation: By extending the graph, along the same slope, above or below measured data
  • Interpolation: By predicting data between two measured points on the graph.
Here are just a few common examples of the types of graphs and charts that you may see on the Science test:

Line Graphs (Linear or Curved)
A line graph is a good way to look at how one variable changes with respect to another variable. Just by looking at a line graph, you should be able to see whether a trend exists (either over the complete graph or within a specific range). In the graph below, the trend observed is that as time has passed, the concentration of CO_2 has steadily increased.


Bar Graphs
Bar graphs are great for looking at differences amongst similar things. Bar graphs show stacks of numbers of things right next to each other than can be compared instantly. The height of each stack can tell you the number of things, either approximately by the numbers on the vertical axis or exactly by a number label on the stack. According to the bar graph below, Germans represent the ancestry of the greatest number of U.S. residents.


Pie Charts
Think of a pie chart as a pizza pie, with each slice representing a percentage of the whole pie. For instance, “high school” represents 28% of the whole pie in the chart below.


3-D Plots
A three-dimensional plot can connect three variables together. In the plot below, there are three axes representing the three different variables.


Tables contain the raw data from an experiment. Tables of pure numbers can be difficult to interpret. It is up to you to put the raw data into some form (usually a chart or graph) that makes it easier for you to observe the trends.


For instance, if you were to take the chart above and convert it into a graph, you would observe the figure below:


Instead of a chart or a graph, sometimes the test will give you an illustration that will have text within the picture, but usually not with any specific explanations. You are expected to be able to follow a chart or interpret a diagram. Below is an example of a basic illustration of photosynthesis. You should be able to get the main idea out of the picture.


Key Tips

Follow this short procedure to extract a lot of information from any graph. Although an infinite variety of data can appear in graphical form, this same procedure can apply to when reading any kind of graph or chart:

  • Describe the graph: What does the title say? What is on the x-axis? What is on the y-axis? What are the units used?
  • Describe the data: What is the numerical range of the data? What kinds of patterns can you see in the data?
  • Interpret the data: How do the patterns you see in the graph (or chart) relate to other things you know?


Questions 1-3 are based on the following passage.

The types of cancer most prevalent in the United States (or in any country of the world, for that matter) have not been constant. Changing lifestyles, changing behavior, and changing public awareness of the risk factors for cancer over the years have caused different forms of cancer to increase or decrease in importance. This activity gives you a “snapshot” of the important forms of cancer, using data from 1999.


  1. According to the data, which of the following is the most prevalent form of cancer?

    A. pancreas
    B. rectum
    C. lung
    D. colon
  2. Women have a greater overall prevalence for cancer according to the data above. Which form of cancer truly accounts for that observation?

    F. ovary
    G. cervix
    H. breast
    J. thyroid
  3. According to the data, which of the cancer types below also affect men?

    A. ovary
    B. corpus uteri
    C. breast
    D. cervix

Answers and Explanations

  1. The correct answer is D. Of the group listed—pancreas (25,000), rectum (379,000), lung (397,000) and colon (877,000)—colon cancer has the largest number.
  2. The correct answer is H. Of the total number of cancer occurrences in women (4,903,000), almost 40% (2,044,000) is due to breast cancer.
  3. The correct answer is C. A number of males (13,000) were afflicted with breast cancer, whereas men were not affected by any of the other types of cancer listed.


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