Peer Review of “A Physical Activity Mobile Game for Hematopoietic Stem Cell Transplant Patients: App Design, Development, and Evaluation”

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Introduction 1.In general, this section is well written but could have included more details on interventions that have tried to promote physical activity in HSCT patients in other contexts to give a full lay of the land. 2. While the hypotheses around the reasons why the app might encourage walking are logical, it would have been good to include some references to support these, and some of the justification for app content might have been better placed in the Methods section. 3. It might have been good to give an indication of the likely target sample(s) (eg, in terms of age) and information on smartphone ownership in these groups because the population (particularly age range) can be very diverse.It would be interesting to get a sense of whether there was a particular target demographic in mind for this game.

Methods
1. Tied to the comment above, it was nice to see some formative survey work.Again, it would be interesting to get an idea of the age range and other demographics of the response sample and whether these are exactly in line with

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RenderX the target sample for this new game (eg, Candy Crush tends to be more popular among specific demographics). 2. Per the comment above, it was not immediately clear that this paper would describe testing with game experts and a nurse, rather than patients.This could be outlined early in the methodology. 6.The sentence on step counters, "To improve the accuracy of our step counters of our designed WW, we recruited 5 additional usability evaluators who were nursing informatics graduate students," could have been described in the Methods section, as it came out of the blue in the Results.
In general, clarity on who comprised the usability samples (survey respondents, testers, additional usability evaluators, and the actual target sample for the game) would enhance the paper.

Discussion
1. Discussion and conclusion are very short-it would have been good to describe more current findings in relation to other relevant studies.Another sample of 30 individuals (students and programmers) was described here, which seems like it might be planned work, but this was not entirely clear.Perhaps a flowchart or table with all of the planned steps and samples involved would be useful. 2. Per the general comment at the start, the focus seems very expert heavy, with only a brief evaluation with patients and a strong focus on usability rather than the impact on walking behavior.It would be important to trial the app in patients to determine whether it has an impact on walking behavior.
To what extent does it matter whether people find it usable and like it if it does not actually change the target behavior?
3. Table 1 looks like it discloses emails; this should be removed if they are genuine. 4. Aside from replicating the model of Candy Crush, was there any consideration for, or attempt to, include some of the key behavior change techniques that are important for physical activity change (eg, goal setting, self-monitoring, feedback)?I can imagine they are probably in there by default, but it would be nice to see which behavior change techniques map to which game features and if there was any consideration of a theoretical basis in the app development process. 5.The qualitative analysis is not mentioned until the Data Analysis section-what was the purpose and how was it carried out?It is worth acknowledging in the Methods to provide context.In addition, I found the sentence describing the qualitative analysis difficult to follow.Could this be simplified?