Reviewer response for version 1
This paper addresses an important gap in the available data regarding the biomedical workforce in the UK. 
Although larger studies are needed (both in the scope of the questions asked and with a larger and more representative population of respondents), this survey is a nice example of how members of the community can begin to address the gaps in existing data collection and dissemination efforts.
Abstract
Please include the number of respondents analyzed and mention something about how the survey was advertised/the target audience. 
(The caveats about survey responses necessarily being biased to those who were aware of it and cared enough to take the time to respond are buried fairly far into the discussion, and it would be helpful to make some reference to this a little earlier in the paper.)
Data presentation
Please state clearly throughout the text the number of responses analyzed in each category. 
(How many UK-based biomedical researchers responded to the survey? 
How many PhD student and postdoctoral respondents were there? 
Etc.)
It would be interesting to include a figure showing responses to the final question (how comfortable do you feel about your long-term prospects in research?"); 
as respondents had the option to select multiple answers, it would be nice to see the percentage selecting each of the possible answers.
For clarity, the colorblind, and those who still prefer to print papers in black and white, it would be preferable to directly label the data in figure 1, rather than using the key. 
Please label the percentage of respondents in each age group; and label graph axes. 
Though more typical for an infographic than a figure in a paper, I do like the text boxes highlighting the take-home message for each panel.
I also initially found the visual representation the hourly salary data somewhat confusing; it might make more sense to make the "hourly salary" its own panel, with bars for minimum wage, PhD, postdoc, and PI average hourly pay (rather than showing the minimum wage three times). 
The hourly salary numbers could be included in or above each bar.
Could you clarify the way average hourly wages are calculated? 
I noticed for grad students, you assumed a 48-hour work week, while for postdocs the assumption was a 45-hour work week, and I didn't see a number for PIs. 
Were the assumptions supposed to represent a "typical" respondent, or an average?
Future directions for the survey
I hope that data collection and analysis for this project will continue. 
I have a few minor suggestions, should the survey be revised.
- I found it somewhat confusing that the category for (predoctoral) graduate students appears to be "PhD researcher."
- While I understand the importance of keeping such a survey short, it might be helpful to collect some additional demographic data, such as gender, relationship/marital status (and if partnered, the partner's salary and discipline), and number of children.
Overall, this work addresses an important knowledge gap. 
I hope data collection will continue and that in future the survey questions can be expanded and the survey itself advertised more broadly.
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