ACT Science: Interpretation of Data

The ACT Science section might be unfamiliar to those who have studied for the SAT. But don’t worry! This section is like a mix of the reading and math sections with a sprinkle of science concepts. From the ACT prep guide, the content can range from biology and chemistry to Earth/space sciences like geology. You don’t have to be a pro in any of these fields in order to answer the questions. You’ve simply got to understand the importance and relationship of what the passages are talking about on top of the knowledge you already have.

This topic is one of the four scores you'll get for the science section of the ACT. Let's see what ACT wants you to do for this topic: "This category asks you to manipulate and analyze scientific data presented in scientific tables, graphs, and diagrams (e.g., recognize trends in data, translate tabular data into graphs, interpolate and extrapolate, and reason mathematically)."

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So this topic focuses on the how and what scientific data is trying to present. First, you should see an example of each data presentation: tables, graphs, and diagrams.

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When you first see these, make note of their features. Below is an example with the table from before.

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Note which table it is. Does it correspond to the information given in a specific passage? Or does it correspond to another figure? Noting which table is important because questions can refer to a specific table (“According to Table 1…”). See what is being measured and its units. This is important because time could be measured in minutes or hours, but it was measured in seconds here. The same goes with speed: it could have been measured in meters per second but it is feet per second in this table. Also make note of other details, such as how many trials there are. Lastly, in this table, the average (or mean) was kindly given, but you’ll likely have to solve for that on your own.

As you can see, there’s a lot to take in from just the table! Now, let’s go over some features of a graph.

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This graph also has units, but they’re shown alongside what’s being measured on the x- and y-axes. The x-axis shows the time elapsed after dosage in hours, while the y-axis shows the mean blood plasma concentration in nanograms per milliliters. You should also make note of the intervals along the axes. Here, time is measured in factors of four, while the mean blood plasma concentration is measured in five. Be careful of these when answering questions! Since graphs are a visual representation of tables, they have a key that makes it easier to see when there’s a lot being compared.

As for diagrams, you should carefully read the passage it corresponds with because it explains what the diagram is trying to represent.

Now that you’ve reviewed the features, let’s talk about the relationships/trends between the values of one variable and the values of the other variable. 

The first way this is described is with correlations. You can have a positive (or direct) correlation, a negative (or inverse) correlation, and no correlation.

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This graph is a good example of a positive correlation ✅. As the peak erosion rate increases, the percentage of wind erosion exposed increases. Even though both are increasing, they’re increasing at different rates. Specifically, Peak D has a stronger positive correlation than Peak C.

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This graph shows both negative correlation ❎ and positive correlation. At first, both types of drug delivery had a negative mean symptom score as time went by. But at a certain point, the mean symptom score began to increase. Be sure to notice these changes because you could be asked about them! As for a no-correlation graph, the point would look scattered.

Let’s see some trends in another type of graph.

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In this bar graph, there’s no line to show you a correlation easily, but you can look closer to see that there’s a trend. You see that there are seven fish species, A to G, and their survival rate is measured in two things: unfiltered water and bacteria-filled water.  All the fishes survive differently in either water. One thing you can easily notice is which fish species has the greatest survival rate and which one has the lowest survival rate.

Before we move on, let’s quickly review some helpful mathematical relationships and equations. Below is a good summary of several types of graphs.

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The equations for each can be used to find relationships in tables, as well!

Now that you know how to point out important information and trends from tables and graphs, you will learn to translate from one presentation to another. This can be tables to graphs or graphs to tables!

Let’s see an example below:

You first have to look at the table this question is asking about.

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First, let’s note some features from this table. You can see that the peak section height is measured in meters, and the percentage of the year that the peak section is exposed to wind has no units. It’s clear that the peak section height is increasing, but let’s see the trend in the percentages.

As you can see, the percentage of the year exposed to wind increases as the peak section height increases. Make note that some intervals increased more than others.

Let’s look at the answer choices:

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You know that there is a positive correlation between the x and y values, so you can immediately cross out B and D since the line is going down. Both A and B have the positive correlation we’re looking for, but only one can be right!

Graph C shows that as the peak section height increases, the percentage increases roughly the same amount each time. Graph A, however, says the increase in percentage went from a little bit to a lot, hence why the arrows get steeper. It also says that the percentage would decrease when it gets to 6 meters.

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But this cannot be true since the analysis of the table shows that when the height increases, the percentage does, too. So, the correct answer is C!

See, it’s not as hard as it may first seem! You’ve just got to know enough about what you’re given to correctly shift it.

The next skill relates to the last question. Remember when you had to guess what the graph looked at 6 meters even though it wasn’t on the table? That’s called extrapolation, when you take what you already know to try to guess what might be! Questions like these ask you to guess a value outside of the given values in a table or graph. On the other hand, there are also questions that require interpolation, which is estimating the value between two points. These are easy to solve once you know the trend in the data.

Let’s start with an example that requires extrapolation.

For this question, the passage has only one table to refer to, which is shown below.

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Since the question is only asking about day 13 for Star 1, you don’t have to find the changes in Star 2, 3, or 4. We see that the x-ray distortion for Star 1 increased by 0.75 m every 3 days. Since day 13 is three days after day 10, you only need to add 0.75 m to the value on day 10 (3.25 m). So, 3.25 + 0.75 = 4.00 meters, which is answer J.

Let’s look at an example of interpolation.

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You can see the concentration of solute for six different dissolved substances is measured at different temperatures in Celsius. Since this question only focuses on HCl, the only columns you really need to pay attention to are circled.

The question asks you what the temperature of HCl is at 70 Celsius, but the given concentrations are at 60 C and 80 C. Since 70 C is right in the middle of 60 C and 80 C, all you have to do for this question is to find the middle value between the given concentrations, 55 g/100 g H2O and 48 g/100 g H2O respectively. The fastest way to do this is to add the concentrations and divide by 2: (55 + 48) / 2 = 51.5. Looking at the answer choices, 51.5 g/100 g H2O is answer choice J.

That’s how to extrapolate and interpolate, my friend! ⭐️

Now that you’ve learned a lot about what to do with one presentation of data, you’ll need to know how to compare and combine data from more than one of those.

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The question is asking to take information from Figure 1 and find its corresponding information in Table 1. The first thing you need to look at is which fish species had the lowest percent of survival when exposed to bacteria. Using the key, the darker colored bars represent the fish exposed to bacteria, and the smallest bar represents the lowest percentage of survival. You can see that fish species A meets both of these.

But the question is asking which habitat this fish species lives in, which can only be found in Table 1. Looking at Table 1, fish species A lives in shallow water with plants. This is answer choice B, which is the correct answer!

When you're taking a test, it is so easy to skip over important information when skimming the passages and questions. To prevent yourself from making a simple mistake that'll cost you a question, write all over your paper! 📝 Underline important parts of the question, circle the specifics, and cross out incorrect answers. You're not scored on what you write on the test booklet but on what you put in for your answer. So write away!

Because this topic focuses on data interpretation, you have to pay attention to the units of tables and figures. Specifically, make of whether the units given can be converted into larger or smaller units. Knowing basic unit conversion is helpful. A question may ask you a measurement in minutes based on a table with units in hours. The answers may trick you into choosing an answer in the table or figure units rather than what the question is asking about.

The nice thing about data interpretation questions is that they almost always state which table, graph, or diagram you can find the answer to. What out for the phrase "according to." If it's not stated, then the data presentation can still be easily found based on what the question is trying to find. For example, if the question is asking for temperature and time, and there is one graph measuring temperature and time and one table measuring concentration and time, you know that you have to look at the graph. Another tip is that the passage may be separated into sections based on the experiment. Each experiment likely has only one data presentation that shows the results. If a question asks about an experiment, then you know you have to look at the data presentation corresponding to that experiment.

Even though the ACT science section doesn't allow a calculator, you still have to calculate for some questions. This can be finding an average or midpoint in a table or graph. Don't rush through your calculations especially since you don't have a calculator. It can be really easy to make a simple mistake in trying to run against the clock.

Like any test, the ACT science exam sometimes likes to give answers to throw test-takers off course. This can be through answers that are very similar to each other (2 answers staring with "smaller than" and 2 answers starting with "larger than") or listing answers in numerical order but skipping a number (2, 3, 5, 6). Nevertheless, you should read the answers carefully so that you don't choose the answer that is wrong only because of one thing.

Time to review what you've learned! Since you need a combination of these skills for every question, these questions won't be separated by skill.

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Question 1) Practice question 7. The correct answer is choice B. This question is testing whether you can analyze a table. The question is asking what Sample 3 is made up of the most. Table 1 shows how much sand, clay, and silt make up a soil sample. Looking at Sample 3, it is made up of 25% sand, 35% clay, and 40% silt. The two largest percentages are clay and silt, so that is what makes up most of Sample 3.

Question 2) Practice question 10. The correct answer is choice H. This question is testing whether you can combine information from more than data presentation based on new information. The question is asking what size  the mineral particles would be in a sixth sample. Since the sixth sample was collected near where Sample 4 was collected, you can assume that their composition of mineral particles is similar. From Table 1, you can see that Sample 4 is made up of mostly sand (60%). You can’t know the size of sand particles from Table 1, but you can find it in Table 2, which says the size range is 2.0-0.6 mm. So, it is larger than 0.6 mm, but smaller than 2.0 mm. The only answer choice like that is answer choice H, the mineral particles would predominantly be larger than 0.06 mm.

Question 3) Practice question 11. The correct answer is choice D. This question is similar to question 10, but you look at Sample 2 instead of Sample 4. Sample 2, according to Table 1, is made up of mostly clay (75%). Table 2 says that clay particles have a size range less than 0.002 mm. The only answer choice less than 0.002 mm is D, 0.001 mm.

Question 4) Practice question 14. The correct answer is choice F. This question is testing whether you can translate a part of the given table into a graph. Specifically, it wants you to find the corresponding substance that has the same trend as the graph. You can see from the graph that the temperature and concentration of this substance have a negative (inverse) correlation since increasing temperature causes the concentration to decrease. Now, all you have to do is see which substance from Table 1 follows this. The only substances that follow this are HCl and NH3, but only HCl is an answer choice.

Question 5) Practice question 19. The correct answer is choice D. This question is testing whether you can analyze the graph with the information given in the text. In the experiment summary, it says that the amount of carbon dioxide shows the level of fermentation. So, more carbon dioxide = more fermentation. Since the question is only asking for the highest level of fermentation after 1 day, you only need to look at the Day 1 column. You can see that test tube 5 has the greatest amount of carbon dioxide, with 86 mm, so it has the highest level of fermentation.

Question 6) Practice question 14. The correct answer is choice G. This question is testing whether you can determine how one variable changes according to another. The question is asking what happens to the temperature as the pressure increases. From the key, you can see that the pressure is the dotted line, while the temperature is the solid line. When the pressure is increasing (the dotted line is going up), the temperature looks like it is decreasing (going down). So the temperature only decreases as pressure increases.

Question 7) Practice question 34. The correct answer is choice F. This question is asking you to translate the given table into a graph. Looking at the table, you can see that as time goes by, the mass of all the rocks increases. From the experiment 1 passage, it says that an increase in mass indicates the rock is reaching the saturation point. This means the graph would have a positive (direct) correlation since the saturation increases as mass increase as time goes by. The only graph that looks like that is the first table, with the line going up.

Question 8) Practice question 6. The correct answer is choice J. This question is asking you to extrapolate a point outside of the table when given new information. Specifically, it says that at a new point 300 meters from the golf course, the average phosphate can be estimated from the table. Looking at Table 2, the distance from the golf course is measured every 100 meters. So, you first have to find the phosphate concentration averages at each distance. At 0 meters, the average is (35.6 + 42.3 + 46.9 + 57.0) / 4 = 45.45 mg/L. At 100 meters, the average is (31.8 + 29.4 + 30.1 + 37.9) / 4 = 32.30 mg/L. At 200 meters, the average is (25.3 + 24.6 + 25.5 + 24.2) / 4 = 24.9 mg/L. Since the averages are decreased at each distance, the average at 300 meters would be less than the average at 200 meters. The only answer that is less than 24.9 mg/L is 20.1 mg/L.

Question 9) Practice question 3. The correct answer is choice C. This question is asking you to analyze the new information given based on what you already have. You’re given a table with new measurements, and you’re told that these measurements are greater than those at one of the sites from Table 2. Let’s start by comparing the A2 column of both tables. Table 3 has 4.1 pinecones, and Site 2 has less pinecones (3.2 pinecones). For the A3 column, Table 3 has 6.4 pinecones, and Sites 1, 2, 4, and 5 have less pinecones. For the A4 column, Table 3 has 1.9 pinecones, and Sites 3 and 4 have fewer pinecones. For the A5 column, Table 3 has 0.3 pinecones, and only Site 4 has fewer pinecones. The Site that had fewer pinecones for most of the columns is Site 4, which is answer choice C.

Question 10) Practice question 38. The correct answer is choice F. This question is testing whether you can determine if there is a relationship between the variables and predict what might happen with changes. Specifically, you’re asked to predict what will happen to the pressure as depth increases. Looking at Figure 1, the depth axis on the left has increasing values as it is going down. This is the same for the pressure axis on the right. So, since both depth and pressure increase in value going down the axes, their relationship must be positive (direct). Therefore, when the depth increases, the pressure must increase as well.

That's an overview on interpreting data in ACT science section! Be careful not to rush through the steps because the details are important! Remember that all you need to answer a question is already there, so don't overthink the question.

Think of the data as a visual representation of the experiment results. If you can imagine each passage as another fun project you could do, it'll be easier to analyze the results!

Here is the collection of ACT practice questions where all of the examples in this guide came from!

Good luck on the rest your of ACT studies! 💖