Do you know the correct way to read a graph?

ACT graphing SAT
By Cal

Reading graphs correctly is an important skill to develop.

Not being able to read graphs won't just affect your scores in math and science. Literacy is at the core of the SAT and ACT, and each section tests literacy in different ways. In the reading section, you will be evaluated on your comprehension of prose. The English section tests conventions of writing and grammar. The math section tests fluency with numbers, functions, and shapes. The science subject matter introduces a different type of literacy — the ability to read and interpret scientific results. 

Why is it important to know how to read scientific figures? Just like reading a book, reading them in the correct way will make more sense. It's kind of like learning how to read in another language. English is read from left to right, Arabic and Hebrew from right to left, and Japanese and Korean, which can be read in columns from top to bottom.  

In science, there are three major types of data representation — graphs, tables, and diagrams. Many students lack a systematized and directional reading method, especially when these figures get complicated. What does that mean for you?  

Learning to read scientific figures before you take the test will give you an advantage, and improve your score. 

This type of literacy will help you become much more comfortable, quick, and accurate on the ACT Science and SAT Math or Reading sections. They all contain data representation. Of course, it will help you beyond the tests, too (more on that in my next post!). Literacy with graphs, tables, and diagrams helps in all fields of science, including everything from the social sciences to reading the newspaper.  

This is how to read a graph:  

  1. If there is a title, start by reading it. Like a book, the title might not make sense until the rest of the graph is read (note: most ACT graphs do not have a title; more on this below. 
  2. Observe all aspects of the x-axis. Read the x-axis label, units, and range.
  3. Observe all aspects of the y-axis. Read the y-axis label, units, and range.
  4. Note the sets of points, number of lines, or types of bars in the graph. Use the key, and read what each is labeled as.  
  5. Lastly, observe any trends in the graph.  

 

Trends are read like this: “As the [x-axis label] increases, the [y-axis label] goes up? Down? Stagnant? No clear trend?” It is also good to observe where any extreme values are — what is the largest x and y value? What is the smallest?  

These final assessments of trends and extreme values intuit the expected level of comprehension and actual questions the SAT and ACT ask about scientific figures.  

Some examples from the ACT 

Here is an example of a “normal” graph from the ACT that’s good to practice with. You can read it using the same order described above. 

Screen Shot 2024-10-03 at 1.59.48 PM

Here’s a trickier graph. The x and y axis are switched. In most data representation, the x-axis is normally reserved for the independent variable, and the y-axis displays the dependent variable. The ACT commonly switches the axes only with depth and height plotted as y. This is important to notice as CO2 is not “causing” depth, below. Plotting depth and height on the y-axis is a visually intuitive convention, and an allowable violation of graphing rules.  

Screen Shot 2024-10-03 at 2.00.34 PM

Here’s another ACT example; it’s more intimidating at first, but it’s still, just a graph! Although this looks more complicated, we’re dealing with three standard graphs that consist of x and y axes. You should follow the order of observing all aspects of the x-axis first, then the y-axis (here, on both sides), then trend.  

In this example, you may think the trend sounds like this: “as symbol eighteen O increases, depth decreases.” But remember, the trend should actually be read, “as depth decreases, symbol eighteen O increases.”  

 This is also a good figure to prepare yourself to see symbols or words you may not recognize — in this case, lowercase Greek delta δ. The symbol is never defined in the passage, and its correct identification does not affect the interpretation of the graph, or passage answers.  

Screen Shot 2024-10-03 at 2.01.33 PM

Here’s another just a graph! Like the figure above, this graph is the result of multiple graphs arranged together — four graphs with a common y-axis. This graph is an important example of why one should invest time in reading the axes labels, ranges, and units before embarking on interpretation. When you see an intimidating graph like this, you have the tools to read and understand the trends — you just need to follow the same steps as you would for any graph, starting with the first x-axis, “TSI (watts…” 

Screen Shot 2024-10-03 at 2.02.28 PM

What about SAT graphs? 

SAT graphs are much more likely to have a title, while most ACT graphs do not. The SAT graph title usually supplies essential information about the graph. If it was missing, the graph would be meaningless. Often, the title holds information that would normally be a part of the axes’ labels. 

This graph is missing a y-axis label, which has been placed as the title: 

Screen Shot 2024-10-03 at 2.03.42 PM

Here’s another. This graph has a vague y-axis label — “Amount…” From the title we learn that it is the amount of “Coffee Profits.” 

Screen Shot 2024-10-03 at 2.04.26 PM

Why is it important to read graphs in this way?  

 When I go over this with students, I usually save this in-depth explanation for last, so it's not information overload. Also, I feel after reading these figures, your brain is primed to receive this information.  

The reason that graphs are read in this order is informed by the design of the experiment and the scientific method. You should read the x-axis before the y-axis because the x-axis is the independent variable. This is the variable that was first manipulated by the scientists. How was it manipulated? This is explained in the units and range of the x-axis. Why were the scientists manipulating this variable? They wanted to study its effect on the y-variable, or dependent variable. How did they measure these effects? This is stated in the units and range of the y-axis. Did the scientists perform multiple trials in their experiment? This information is in the key of the figure.  

After you have grasped the experimental design, like the order of scientific experimentation, now you can fully appreciate the results or trends of the experiment. In essence: what happened? 

Once you have proficiency with graph reading, you usually naturally expand your curiosity about the results. You start to go beyond the simple “as x increases, y increases” observations, to notice more idiosyncratic patterns and trends. I find that acquired curiosity leads to intuition about the more difficult types of questions the ACT and SAT ask about figures.  

Who else reads graphs in this way?  

Scientists! OR people who are science literate. Even at the highest level of graph reading, people still have to read each element of the graph in this order. This is the way that results are presented in academic talks and at scientific conferences. The presenter will read the graph step by step to the audience in the order described above (I know because I have been there). When students have mastered this type of graph reading, they sound like professors! Good science is practicing science literacy.  

Cal graduated cum laude from the University of Connecticut with a BS in Ecology and Evolutionary Biology. She was a National Science Foundation (NSF) Graduate Research Fellow during her PhD in Biological Anthropology at City University of New York, and was an NSF-funded Postdoctoral Researcher at Arizona State University’s Center for Evolution and Medicine.

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