The validation of this study followed and applied a well-established process of cross-cultural adaptation [16], translation and back-translation, review, piloting, and psychometric evaluation.

First, the translation of MARS from English to French was conducted by two independent bilingual scientists (IS and LF). Following the review, discussion, and comparison of their two forward translations, they agreed upon a common pilot version of MARS-F. Second, this common pilot version was blind back-translated by two bilingual native English speakers with different educational backgrounds—a researcher in public health and educational sciences (ED) and a nonacademic professional (ADB). Third, the two bilingual scientists (IS and LF) compared the back-translated version with the original English version. After mutual discussion, they agreed upon the final French version of the scale (MARS-F). Finally, 6 other people (3 researchers and 3 nonacademic professionals) evaluated the comprehensibility of this finalized French version. Their comments were considered, and the final MARS-F version was thus created (Multimedia Appendix 1).

The inclusion process consisted of three different phases: searching, screening, and determining the eligibility criteria of nutrition health-related apps. The search for apps was conducted from March 10, 2021, to March 17, 2021, on the French Apple Store (iOS) and Google Play Store (Android). No truncation or use of logic operators (AND, OR, and NOT) was possible while searching in the Google Play Store and iOS Store. Hence, in order to select the nutrition health-related apps, the following search terms were used separately: “nutrition” (nutrition), “diététique” (dietetics), “alimentation” (food intake), “régime alimentaire” (diet), and “manger sain” (healthy eating). Apps were included if they were available free of charge or at least free of charge during 7 days from both the iOS Store and Google Play Store. Duplicate copies of apps between the two stores were excluded, resulting in a total of 63 apps (Figure 1).

To complete the evaluation process of apps, we used the rating methodology previously described by Stoyanov et al [8]. We made a video with an introduction of the French MARS scale, and an exercise on how to rate a nutrition mobile app (available on request to the corresponding author). Two individuals with a master’s degree in medical sciences (FC and PM), and who were fluent in both French and English, were instructed on how to serve as raters by watching the video. With a view to ensure that the raters were sufficiently trained, they were asked to download and evaluate 10 apps that were randomly selected from those meeting our inclusion criteria using MARS and MARS-F. Each app rater tested each app for at least 15 minutes before they carried out their evaluation. Raters then compared their individual rating scores for each app. When their individual rating scores varied by at least 2 points, they discussed their findings until they aligned their rating approaches and agreed on the score.

Among the 10 common apps, the mean scores of the dimensions engagement (t₁₀=–0.76, P=.44), functionality (t₅₃=–0.11, P=.90), esthetics (t₅₃=0.22, P=.82), and information quality (t₃₃=–0.35, P=.72) were equivalent in both versions. The internal consistencies of MARS (ω=0.86, 95% CI 0.56-0.96) and MARS-F (ω=0.78, 95% CI 0.32-0.94) were good and acceptable, respectively, and the MSA revealed strong scalability (H=0.47; SE=0.07).

The ICCs for MARS (0.88, 95% CI 0.79-0.93) and MARS-F (0.89, 95% CI 0.8-0.93) were high. The mean and SD scores of the items in MARS and MARS-F are presented in Table 1. The mean scores of the dimensions engagement (t₅₃=–0.34, P=.72), functionality (t₅₃=–0.47, P=.63), esthetics (t₅₃=.09, P=.92), and information quality (t₃₃=0, P>.99) were equivalent between MARS and MARS-F.

The internal consistency of MARS and MARS-F and their subscales is presented in Table 2. The internal consistency of the MARS dimension engagement (ω=0.82, 95% CI 0.79-0.87) was good. The internal consistencies of the dimensions functionality (ω=0.80, 95% CI 0.74-0.85) and esthetics (ω=0.79, 95% CI 0.73-0.88) were acceptable and that for information quality (ω=0.64, 95% CI 0.49-0.70) indicated questionable consistency. The internal consistency of the overall MARS score was good (ω=0.87, 95% CI 0.83-0.91).

For MARS-F, the internal consistencies were acceptable for the dimensions engagement (ω=0.79, 95% CI 0.72-0.83), functionality (ω=0.79, 95% CI 0.73-0.85), esthetics (ω=0.78, 95% CI 0.71-0.82), and information quality (ω=0.61, 95% CI 0.53-0.65). The internal consistency of the overall MARS score was good (ω=0.86, 95% CI 0.85-0.90).

The correlation coefficients between the corresponding dimensions of MARS and MARS-F ranged from 0.97 to 0.99. P values were adjusted for multiple testing according to Holmes’ method (Table 3). Correlations between the respective items are presented in Multimedia Appendix 2.

MSA results for both versions of the scale (ie, MARS and MARS-F) are summarized in the Table 4. MSA for MARS revealed strong scalability (H=0.37; SE=0.03). There was no violation of monotonicity because the item step response functions were nondecreasing functions; likewise, there was no violation of nonintersection because the item step response functions do not intersect. The internal consistency of this scale was acceptable (MS=0.88; λ-2=0.88; LCRC=0.89). MSA for MARS-F revealed good scalability (H=0.35; SE=0.03). The internal consistency of this scale was acceptable (MS=0.88; λ-2=0.89; LCRC=0.90). The scalability results of MARS and MARS-F are presented in Figure 2.

This study aimed to develop and evaluate MARS-F to enable French health care professionals to assess the quality of mHealth apps. To our knowledge, this is the first cultural adaptation, translation, and validity evaluation of the original MARS in French.

Nutrition-related apps were identified using well-defined and selected search terms in both two app stores (Google Play Store and Apple Store). This was done to avoid methodological challenges such as ranking algorithms or irrelevant results because the indexing of apps is usually determined by a developer who is most interested in promoting the app.

With a view to provide a comparable interpretation of statistical indicators, the methodology was chosen to be similar to previous adaptations of the scale [2,8,14,26]. In addition, 63 apps were included, which is higher than the minimum sample size of 41 apps required to confirm that interrater reliability lies within 0.15 of a sample observation of 0.80, with 87% assurance [26]. We used the same strategy that led to the Italian version of MARS except that the team included apps by searching and screening across three app stores (Google Play, Apple, and Windows Stores). As per the validation of the German version of MARS, each search term was provided separately, as no truncation or use of logic operators (AND, OR, and NOT) was possible in the Google Play and Apple Store. In our study, two raters downloaded and then evaluated 10 apps that were randomly selected for training and piloting purposes as in the initial English version of MARS against 5 apps in the Italian [2], Spanish [13], and German development versions [14].

The interrater reliability of MARS and MARS-F were aligned, with overlapping CI values. The ICCs for MARS-F were also comparable to the Arabic (0.84, 95% CI 0.82-0.85) [15] and German versions of MARS (0.83, 95% CI 0.82-0.85) [14], and they were slightly lower than the Italian version of MARS (0.96, CI 0.90-0.91) [2] (Multimedia Appendix 3).

The internal consistency of the overall MARS score was good and that of MARS-F was acceptable for the dimensions engagement, functionality, esthetics, and information quality. The internal consistency of the German version of MARS was good for engagement and excellent for functionality and esthetics. On the other hand, the internal consistency of information quality was acceptable. For the Arabic version of MARS, the internal consistency was good for engagement and esthetics, good for information quality, and acceptable for functionality [15]. All Cronbach alpha coefficients were judged to be at least acceptable for the Italian version of MARS [2], and these values were high for the Spanish [13] version of MARS.

MSA results for MARS-F revealed a good scalability (H=0.35, SE=0.03), and the use of total MARS-F score was found to be appropriate. Additionally, we obtained a high correspondence between MARS-F and the original MARS [8], which demonstrates proven validity.

The same methodology was used for the validation of the German (apps targeting anxiety), Italian (primary prevention), Spanish (health and fitness apps), and Arabic versions (health and fitness apps). Our results were consistent with the findings of the research teams that developed and validated the Italian, Spanish, German, and Arabic versions of the MARS [2,14,15] (Multimedia Appendix 3).

The first possible limitation could be that the validation of MARS-F is based on the evaluation of nutrition-related apps, whereas MARS is applicable to mHealth apps. The second limitation could be attributed to the fact that MARS-F was elaborated by native speakers living in France. French speakers can have diverse cultures according to their country. Therefore, further adaptation could be required. The third limitation concerns item 19 on information quality. This item could not be rated because raters choose the response option “non applicable,” which allows raters to skip an item if the app does not contain any health-related information (eg, nutrition apps in this study). The same item was also excluded from all calculations in the Italian version of MARS because of lack of ratings [2]. This item evaluates the evidence-based literature relating to the nutrition app assessed, and it is worth noting that many apps have not yet been scientifically evaluated.

With 300 billion French-speakers worldwide [27], the translation of MARS could be of special interest. Owing to its wide use in the assessment of mHealth apps in the scientific literature, we chose to translate MARS into French to provide a reliable and understandable tool for health professionals to get an evidence-based sense of the quality and reliability of chosen mHealth apps. Other rating scales such as App Quality Evaluation (AQEL) [28], ENLIGHT [29], and the app evaluation model from the American Psychiatric Association [30] could also represent relevant tools to evaluate mHealth apps for further investigations. All these scales were created for the evaluation of mHealth apps, except AQEL that specifically evaluates nutrition-related apps [28]. Several studies have demonstrated that nutrition is one of the key factors in oral and general health [31]. It would be interesting to translate this scale into French and to evaluate the nutrition-related apps included in our study.

Alongside the assessment process of mHealth apps, the patient’s involvement in such processes should also be considered. The user version of the MARS (uMARS) [32] should be translated and evaluated for reliability and validity. Mobile technology represents an innovative opportunity to assist end users in improving their management of their chronic conditions. Such in-the-pocket devices could be adapted to the specific needs of populations. As an example, mHealth apps could be used for young people’s transition to adult care services [33], to support active adults [34], or to promote healthy aging [35]. mHealth apps are valuable for the primary and secondary prevention of chronic diseases, especially for controlling individual risk factors and preventing the snowball effect of chronic diseases with aging [31].

To conclude, MARS-F would be a crucial aid for researchers, health care professionals, public health authorities, and interested third parties, to assess the quality of mHealth apps in French-speaking countries. In addition, French app developers could use this French version as a tool to evaluate and improve the quality of their apps prior to market launch. MARS-F is an important cornerstone to app quality assessment with the purpose to identify reliable and valid apps for the benefit of end users.