Figures are critical components of how scientists share their research findings. And they pop up in all sorts of places - scientific publications, news articles, posters, talks. Sometimes a figure consists of a single graph (which can be daunting to interpret on its own) but more often than not they are large panels with multiple data types (e.g. images, models, graphs) that can be overwhelming at first glance. Because figures are so central to how we communicate science, it is important to be comfortable with interpreting and critically evaluating them. Here we’ll use an example of a figure from a cell biology paper to practice some strategies for breaking down a figure.
Intro to Our Cell Biology Example Figure
The figure below is from a primary research article published in a scientific journal. It contains three different types of information - schematics, images, and graphical data - that are all grouped together for a reason. It is a relatively simple figure, but even so there are a lot of details you could dive into in order to evaluate the it. We won’t go through every detail of the figure or address every possible question one could ask about it, but hopefully the strategies below provide a systematic approach to interpreting a scientific figure and get you thinking about the types of questions to ask.
Figure 1 from Irgen‑Gioro, et al. 2023, licensed under CC BY 4.0.
Interpreting a Scientific Figure in 3 Steps
1. What is the question?
Every figure started with a question and the figure is the authors’ way of trying to show you the answer to that question. In order to interpret the figure, it helps to know what the question was and the conclusion that the author is trying to convey. There may be multiple small questions wrapped into one figure, but each piece is likely contributing to some larger question that ties them all together.
What is the question that the example figure is trying to address? The first place to look is the Figure Legend - the bit of text associated with the figure itself. The start of a figure legend is often a statement describing the overall conclusion the author wants you to take away from the figure. In the example, I highlighted this statement in yellow. The statement is written as a conclusion, but we can reframe it as a question - Can fixation change the apparent liquid–liquid phase separation (LLPS) behaviors of proteins?
Before moving on to the next step, make sure that you understand the question and any key terms that may be unfamiliar. For this example, it would be important to know what fixation is and what liquid-liquid phase separation is in the context of biology.
2. What are the methods?
Next, try to determine how the authors went about addressing the question. Often (but not always) the figure legend will briefly describe what methods were used to generate the data shown in the figure. If the figure is in a paper, another place to look for this information is in the text around where the figure is cited in the article.
For this example, the figure legend nicely summarizes the whole experiment that the authors performed and includes important details such as: the different proteins expressed (EGFP- EWS(IDR), EGFP- FUS(IDR), and EGFP- TAF15(IDR)), the cell type used (U2OS), the experimental treatment (4% PFA for 10 min), the imaging method (confocal fluorescence microscopy), and their quantification strategy (measurement of apparent LLPS parameters before and after treatment). The schematics in the figure itself also provide information about the methods, by providing a visual representation of the three different proteins that they expressed.
At this point, you may need to pause again and do a little background research on the methods that were used. You don’t need to become an expert in them, but it is important to make sure you are at least familiar with the main goals and limitations of the methodology before you try to evaluate the resulting data. In this case, it may help to ask questions like what are those proteins they expressed? What is confocal microscopy and a maximum z-projection? How does PFA work? What do the three parameters they measured refer to?
3. Do the data make sense?
Once you know what the figure is trying to communicate and how the authors addressed their question it is time to evaluate. Put your Evaluating Graphical Data skills to work for assessing the graphs, but remember to consider other data types as well. How do any images relate to any graphs? Do the corresponding image and graphical data seem consistent? As you assess each part of the figure, keep track of the conclusion you draw from the data. At the end, ask yourself if you think the data answered the overall question of the figure. Does the data support the author’s conclusion?
For this example, you might ask yourself if you believe there is an observable difference between the Live Cell and Fixed Cell images. What differences do you notice? Do the graphs make sense with your observations? Does it make sense to show “% Change” and not the actual measurements for pre- and post-fixation for the three parameters they measured? Overall, do you think these data address the question of whether fixation changes the apparent behavior of proteins?
As with every skill, interpreting figures takes practice and, at first, you will probably need to take a lot of pauses to look up background information. For figures in publications, some of that background information will be in the main text of the article. So why not just read the article and refer to the figures as you go? Focusing on the figure and reading just enough of the article to collect relevant context allows you to evaluate the data in a more unbiased fashion so you can make your own interpretations. It is also good practice for when you encounter figures in other contexts.
Figures are places where scientists can bring multiple, complementary types of evidence together to try to answer a question. By establishing what question the figure is trying to address and the approaches the scientists took to address it, you can be better able to critically assess all of the data presented to form your own conclusions.
Reference
Irgen-Gioro S, Yoshida S, Walling V, Chong S (2022) Fixation can change the appearance of phase separation in living cells. Elife 11:e79903. https://doi.org/10.7554/elife.79903