Take a random scientific paper and look at Figure 3, without looking at the rest of the text. Can you understand what experiment each panel shows? Do you know what all the acronyms, different colored fonts, and symbols mean? Do you know what analysis was performed, how many replicates (biological and technical) the authors conducted, what statistical tests they used, the sample size, and the nature of the error bars? If so, then thank the figure legend.
Here are some suggestions if you want your figure legends to be truly legendary:
1. Give the figure a descriptive title that summarizes the main point of the figure (here’s where you can interpret the results!). Do not refer to panels in the title. Also do not define acronyms/initialisms in the title. However, you can describe the main conclusions of the figure in the title.
2. Do not interpret your results. In the rest of the legend, provide enough information that the reader can understand the experiment, interpret the data, and come to their own conclusions. But the author should not draw conclusions in the figure legends–you have the results and discussion for that.
3. Do provide enough description so the figure can stand on its own.
- Mention all panels–make sure the differences between panels are clear.
- Mention all lanes, samples, etc. (including the controls!)
- Name the methods used, but don’t provide a full methods section. (Make sure readers can tell what kind of data they are seeing and what the controls are).
- Define the meaning of any symbols, such as asterisks, letters, arrowheads, etc.
4. State your statistics, including the threshold for significance, statistical test used, and number of replicates. Also indicate the number of biological replicates, which values were compared in statistical analyses, and if the results are normalized to a specific value.
5. Define all acronyms/initialisms and use them consistently with the main text. Don’t use the same acronym to describe two different things (e.g., SD–standard deviation/short days). If needed, describe any features that the reader needs to understand, such as the meaning of a particular color. However, try to design your figure so this is not necessary.
6. Keep it brief. Yes, now that we’ve told you to include all this other stuff, you still need to be concise–we’ve seen 100–300 words as a good amount of text. Don’t state the obvious–“images of” and “are shown”.
Finally, keep in mind that different journals have different requirements for figure legends, so read the journal instructions for authors and look at other articles in your target journal to get a good feel for what they want in the legends!