Release Date: June 26, 2015
Category: Scientific Writing
Author: Michelle S., Ph.D., E.L.S.
Figure legends are an often overlooked component of your publications, proposals, and posters. However, these short blurbs of text are a valuable part of your scientific writing because they have the responsibility to describe the most important part of any paper: the figures. Good figure legends can be the difference that takes your paper from a “necessary” read to an enjoyable one. By making your figures easy to understand, you save your readers time and give them a reason to like your work, both now and in the future. Here, we offer some tips on what to include in your figure legends to elevate the quality of your manuscripts.
Figure legends should support your figure entirely, meaning that the reader of your paper should be able to understand your figure, paired with its legend, without going to the results or methods sections to see what you say about your observations or how the experiment was done. By designing your figure legends to support your figure independent of the main text, your readers can quickly draw conclusions from your figures, and then return to the results section to compare their thoughts with yours. It allows the reader to have a more engaging experience with your research. If they can quickly interpret your figures on their own, they will likely read your text with more anticipation and interest. This is the sort of experience writers should strive to create for their readers.
So how do you write a great figure legend? One way to write a great figure legend is to think of it like a miniature abstract for the figure. There are four components that should be in every figure legend:
Title– The title of a figure legend should describe the figure, clearly and succinctly. A strong title is often written in active voice, and may summarize the result or major finding that you are drawing from the data in the figure (e.g., XX compound inhibits the growth of lung cancer cells). Titles may also be a descriptive phrase instead of a complete sentence, often stating type of analysis used (e.g., Flow cytometry analysis of CCR5-expressing cells.) If you have multiple panels in your figure (A, B, C, etc.), the title should encompass all the panels in some way. If you have difficulty coming up with a single title to describe all panels in a multi-panel figure, it may indicate that the panels do not fit nicely together. In this case, the panels could be separated into two or more smaller figures.
Methods– These methods are meant to be VERY brief and to describe the design of your experiment. Give only the details necessary to understand the figure. It may be the treatment given to cells or mice, if applicable. It may simply include the type of assay that the figure shows. Include details like the assay name (e.g., western blot, or RT-PCR), antibodies used (if any), and other information that is critical to understand the experiment without the reader needing to turn back to the methods section.
Results– Here, you provide a single sentence on the results shown in the figure. This component of the legend can vary a lot, and might be unnecessary if the title is a results-based statement already (like the first example title above). Regardless of whether your results are given in the title or later in the legend, be sure to include details about the biological replicates you performed, the sample size (n), and p-values if applicable. For example, if a two-panel figure demonstrates that a protease you are studying degrades a substrate, the results statement in the figure legend might say: “Coomassie staining (A) and western blot (B) show the degradation of [substrate] by [protease] in a dose-dependent manner. Results are representative of three biological replicates.”
Figure definitions and descriptions– Invariably, figures will contain symbols, lines, colors, abbreviations, error bars, scale bars, and other components that need to be defined and described properly. Make sure that you define these, and anything that might be non-intuitive about the figure, in the legend. Additionally, try to avoid using names/number of plasmids or strains generated in your laboratory as the labels in your figures/legends. These numbers are useful for your organization in the lab, and they should certainly be summarized in a table for the purposes of sharing plasmid/strains with collaborators after the paper is published. But they are a complicating step in the interpretation of the figure. If strain MS301 is actually a deletion mutant for a gene of interest (e.g., ptsH) it is better to label the figure and legend with “ptsH-null” than with “MS301.”
Overall, legends should be succinct but comprehensive. Aim for a length of 100-300 words. It can be preferable to use complete sentences as much as possible, but if you prefer phrases or sentence fragments, the same advice applies with regard to content and length. For consistency, use the same abbreviations, nomenclature and units in the figure that you used in your methods and results sections.
Verb tense is another important consideration for figure legends. Similar to the main text, methods and results are typically written in past tense (e.g., “Cells were treated with caffeine for 24 hours, and then harvested for analysis by western blot using α-phospho-MAPK antibodies”, and “Caffeine exposure increased the amount of phosphorylated MAP kinase”).
Finally, remember that certain journals have specific requirements for the figure legends they publish. Be sure to always review the instructions to authors for your desired journal. If their requirements or recommendations conflict in any way with the suggestions provided here, opt for their requirements. Some examples include high-impact journals like Nature, Science, and Cell. These journals have specific legend requirements, and if you are submitting to these journals, you should write your legends specifically to match their requirements. Regardless of the journal, carefully following the instructions to authors can help cultivate a good experience with the journal’s editors, improve the likelihood of acceptance, and develop a sound reputation for future publications in that journal.
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