The EARS was cross-culturally adapted to the Nepali language and the adapted N-EARS was validated. The N-EARS showed excellent internal consistency and good construct validity. The 6-items adherence behavior scale revealed the presence of only one factor with strong loading. The cutoff score was 17.5 with a sensitivity of 89% and specificity of 78%. The 6-item adherence behavior and 10-item reasons for adherence/non-adherence scale were highly correlated.
Heterogeneous participants with respect to age, gender, and diagnosis were involved in the study. The study site had easy access to the participants from urban, sub-urban as well as rural areas of Nepal. So, the participants comprised of diverse ethnicity and from various geographical regions.
Cross-cultural adaptation
The EARS was cross-culturally adapted to the Nepali language based on Beaton guidelines [7]. The forward and back translation as well as adaptation procedure revealed no content or language-related issues. Through pre-testing, good clarity and understandability of the N-EARS were demonstrated. In contrast to the findings of a study by Meade et al., where re-framing for some items was required [6], there was no need of refining or redefining any item or words while adapting to the Nepali language. The N-EARS was formatted in such a way so that it is concise, short, easy to administer, and looks attractive. In section ‘A’ of the tool, participants did not have any issues in understanding the questions. However, in agreement with the findings from the study by Meade et al., they had difficulty in completing the answers of the questions when exercises were not prescribed in appropriate dosage or, when prescribed dosage was not understood [6].
Reliability of N-EARS
The internal consistency was assessed to evaluate the degree of the interrelatedness among the items [14]. The internal consistency of N-EARS was excellent (a = 0.94) for 6-item adherence behavior [14, 15]. The internal consistency of the original English versions was 0.8 and that of the Brazilian version was 0.88 for 6-item adherence behavior [5, 11]. The present study demonstrated higher internal consistency (a = 0.94) of N-EARS than both English and Brazilian versions. An a value of 0.70 to 0.95 were considered acceptable values [16]. Therefore, the internal consistency of N-EARS of 6-item adherence behavior was comparable with the values of English as well as Brazilian versions and it was within acceptable range.
Since the recommendation was against adding up of items to calculate a final score in 10-items for reasons of adherence/non-adherence, we did not determine the internal consistency of the 10-items [5]. This was not established even in the original English version by Naomi et al. [5] and the Brazilian version by De Lira et al. [11].
Validity of N-EARS
The EFA demonstrated adequate construct validity of the 6-item adherence behavior scale of N-EARS. The 6-item adherence scale revealed a one-factor solution with a strong loading (75.84%) to exercise adherence. The factor loading was higher than that of the original version which demonstrated 71% factor loading [5] and other self-reported outcome measures [17]. We could not perform EFA on 10-item reasons for adherence/non-adherence as it could not fulfill the criteria of sampling adequacy (KMO < 0.60) [13], which was in contrast with the Brazilian version (KMO = 0.64) [11].
The ROC curve was used to analyze the predictive effect of the 6-item adherence scale [18]. The AUC of the total score of the 6-item adherence behavior scale was 0.91 which was statistically significant and suggested a predictive validity which is in line with literature evidence [18, 19]. The cutoff score of the tool was 17.5 with a sensitivity of 89% and specificity of 78% that discriminates adherent and non-adherent participants with respect to exercises. A study by De Lira et al., in the Brazilian version demonstrated a cutoff score of 17 with sensitivity and specificity higher than 80% [11]; findings that are comparable to the present study. We also compared our findings with a study by Wang et al., in which a similar scale for exercise adherence was used. The sensitivity of 87.2% and specificity of 76.3% reported in the stduy was similar to the findings of our study [18].
The cutoff score of 17.5 indicated that any individual obtaining score > 17.5 out of 24 on the 6-item adherence scale is said to be adherent to the prescribed exercises. However, the cutoff score has to be cautiously used during interpretation because without knowing the level of exercise that is necessary for treatment to be effective, a cutoff score in assessing exercise adherence may not be useful [5, 19]. The cutoff score, sensitivity, and specificity reflected a preliminary predictive validity, which was not established even in the original version of the EARS and was a limitation [5]. On the other hand, completely relying on the established guidelines with the back translation reflecting the same item content as the original version supported good face validity of the N-EARS [7, 10, 20].
The correlation between the total score of 6-item adherence behavior and 10-item reasons for adherence/non-adherence demonstrated the validity of the N-EARS. The strength of correlation has been used in describing validity in patient-reported outcome measures [6, 21]. The 6-item adherence scale demonstrated a strong correlation (0.6 to 0.8) with items 1, 2, 4, 6, 7, and 10 of 10-item reasons for adherence/non-adherence in the present study. The reasons for adherence/non-adherence in the participants of a study by Newan-Beinart et al. were item numbers 1, 2, 3, 4, 7, and 9 [5]. Thus, the 10-items adherence/non-adherence gives clear information on reasons for adherence/non-adherence to exercise on one-to-one analysis, which may vary from one participant to another.
Strengths and Limitations
The strengths of this study include: (i) the method of cross-cultural adaptation that followed the established guidelines giving a methodological strength; (ii) the reliability and validity were established on pre-diabetic who were healthy during the recruitment and on patients with various other health conditions as well. We could evaluate the feasibility of the N-EARS on healthy individuals who were recommended for exercises to prevent disease or remain fit and on patients who were prescribed exercises to treat their impairments or, activity limitations. Therefore, the reliability and validity were demonstrated in the heterogeneous group of participants; and (iii) the N-EARS yielded identical psychometric properties as original EARS.
Our study also has some limitations. First, the study had a small sample size. Due to the COVID-19 pandemic, the data collection was stopped, and a preliminary analysis was done with the sample that we had collected before the study was halted in March 2020. Since preliminary analysis met the criteria for sample adequacy, the final analysis was performed with the current sample. Second, participants had to recall how much they adhered to the prescribed exercises during the last two weeks while scoring exercise adherence level. Hence, there might be a possibility of recall bias during scoring. Finally, participants had to be literate in order to respond to the EARS. This is a limitation of the EARS in a context where illiteracy is an issue. An oral response version of the scale would probably be of interest for future research.