Letter to the editor in response to the article of Sada, Abdullahi and Hassan (Hausa translation, cross-cultural adaptation, and assessment of psychometric properties of the motor activity log)

We read the published study by Sada et al. [1] with great interest which translated and cross-culturally adapted the 30-item Motor Activity Log (MAL-30) into Hausa and evaluated its psychometric properties in terms of internal consistency, test–retest reliability and construct validity among Hausa-speaking stroke survivors. We acknowledge the contribution of the authors. Indeed, the availability of the Hausa version of the MAL-30 is of grave importance to assess real-world arm use in the Hausa culture, a language spoken by about 60 million people worldwide [1]. However, we would like to comment on some important issues related to the methodology. First, though the authors stated to have followed the guidelines for the translation and cross-cultural adaptation process proposed by Beaton et al. [2], pilot testing and cognitive debriefing were not conducted to evaluate comprehensibility and acceptability. Pilot testing is one of the critical steps in cross-cultural adaptation process of a patient-reported outcome measure to ensure that the adapted measure is still retaining its equivalence in an applied situation [2]. Preferably, 30–40 subjects from the target setting should complete the new questionnaire and then be interviewed about the meaning of each questionnaire item and the chosen response. All problematic items, responses, statements, phrases and words are resolved at this step. Thus, this step confirms face validity and provides a rough measure of content validity [2]. Secondly, the rationale for the sample size calculation is uncertain. According to Terwee et al. [3], internal consistency using Cronbach’s alpha should be calculated from factor analysis with a minimum sample size of 100 subjects to ensure stability of the variance-covariance matrix. However, internal consistency was evaluated with 64 subjects. Although Rasch analysis for unidimensionality (internal construct validity) was performed, a larger sample size ( 100), however, is generally considered necessary to obtain robust and precise item parameter estimates [4]. Additionally, test–retest reliability and inter-rater reliability were only evaluated using the intraclass correlation coefficient (ICC). It should be noted that ICC is inadequate, since it only takes into account of subject’s variability, but not measurement error [3]. The calculation of standard error of measurement (SEM) and smallest detectable change (SDC) or limits of agreement are therefore recommended for pyschometric validation studies [3,5]. Lastly, in order to evaluate external construct validity, it is important to examine the extent to which the scores of the new questionnaire correlate with scores of other questionnaires in a manner that is consistent with theoretically derived hypotheses regarding the concepts that are being measured [3]. It can be also evaluated by examining difference between relevant known or extreme groups, also referred to as known-groups validity. According to Terwee et al. [3], construct validity is sufficient when 75% of the predefined hypotheses are verified. However, the authors have evaluated construct validity, without formulating a priori hypothesis, by comparing the scores MAL-30 obtained on the Hausa version with the scores obtained on the original English version which can lead to recall bias. Moreover, correlation with other related measures of upper limb function and or impairment such as the Wolf motor function test and Upper Limb Fugl–Meyer was not performed. So, the external construct validity is somewhat contentious.