Do your students have trouble coming up with conclusions to a lab experiment? It may be because your students struggle to interpret graphs..
Results from REAL Science Challenge Vol 2 Contest 1 support this claim. According to test results, about 40% of grade 8 and 9 students cannot correctly draw a conclusion from a graph (Note: we refer to questions #13 and #18 from the contest for this stat). That’s 2 in 5 students (or 12 students out of a class of 30) who struggle with this important science skill. And although a 60% success rate can be seen as being pretty good, it’s not good at all considering these students are in grade 8 and 9. That means they’ve had roughly 8 years of science education – and still can’t interpret graphs.
In this post, we go over the basics of interpreting graphs and coming up with conclusions in 4 steps. We provide some sample graphs for your students to analyze along with a cheat sheet for download.
4 Steps to in helping to better interpret Graphs
1. Identify what the graph represents.
First, look to see if the graph has a title. If it does, it may help to determine the purpose of the graph.
Next, look at the graph and identify the variable or element plotted on the x-axis (the horizontal axis of the graph). Do the same for the y-axis (the vertical axis of the graph).
One can identify what the graph represents by filling in the blanks: “The graph shows the effect of <variable x> on <variable y>”.
2. Check the units and scales on both x- and y- axis.
In other words, what is the unit of measurement of both x- and y- axis? Are measurements in metres, seconds, kg (or another unit)?
And, how much is one line worth? If the x- or y- variable increases one step, how much is that worth?
3. For one value of x, find its corresponding value for y. Repeat for each value of x.
In other words, for each condition along the x-axis, see what the result of that condition is along the y-axis.
4. Compare values of y. Depending on the experimental design, one can either:
A. Compare values of y for each value of x against each other. This is useful to determine which value of x has the greatest (or lowest) value of y. For example, let’s say a graph shows calories burned as a function of exercise type (ie. Running, swimming, cycling, weight training, etc.). If we compare the y-values ( ie. Calories burned) for each x value (ie. Exercise type), we can determine which type of exercise burns the most (or least) number of calories.
B. Compare values of y for each value of x against the control. A control is typically an experimental trial that is identical to other trials with one exception: it lacks a “treatment” of X. For example, say we want to set up an experiment to see how well a new brand of dish soap cleans dishes. First, I run a trial where I soak dishes in just plain water. This is the control.. Then, I do the same thing but I add the dish soap into the water. In both cases, say I measure how well the grease washes off the plate after soaking. If we compare the results of both trials, then we can determine if the dish soap works at all to remove grease. If the results are the same between the control and experimental condition, then the dish soap works as well as water (ie. It doesn’t work) to remove grease from dishes.
Of course, we can always use a hybrid of A and B. In the dish soap experiment, we can also test other dish soaps in the experiment too. That way, not only can we see whether or not a dish soap is effective at removing grease, we can also determine which is the most effective.
In order to get better at drawing conclusions from graphs, students need to practice. It’s that simple. So, where can we get science graphs and data for students to analyze? I like to use Public Library of Science, which is one of a few websites that publish science research articles and allow free access to the journals and their use. Not only is there a variety of science articles on the site, there is a variety of ways scientists choose to represent their science data and graphs (not just bar graphs). I provide a handout that includes some graphs my students have analyzed from the PLOS site.
Drawing conclusions from graphs and data is one of the most important skills for students to be able to do. Students may struggle with this skill simply because no one has stopped to explain how to interpret graphs. Sometimes, it’s due to lack of practice. Sometimes, it’s both. Click the link below to sign up to our email list AND download the handouts to this post – which include the notes above as well as practice graphs.
Until next time, keep it REAL.