Nigerian (Yoruba) version of Disabilities of the Arm,Shoulder and Hand questionnaire (DASH-Y): Cross-cultural adaptation and initial validation

Abstract

Introduction

The Disabilities of the Arm, Shoulder and Hand (DASH) questionnaire is a widely used upper extremity outcome measure. However, it is yet to be translated into any of the major languages in Nigeria, thus limiting its utility in the Nigerian clinical setting. The aim of this study was to cross-culturally adapt the DASH questionnaire into Yoruba, a major Nigerian language and investigate its initial validation.

Methods

The English version of DASH was adapted into Yoruba through forward–back translations, experts’ committee meetings, pretesting and cognitive debriefing interview in accordance with the guidelines recommended by the developers of DASH. Fifty-two purposively selected patients with upper extremity musculoskeletal disorders participated in a cross-sectional survey. Factor analysis was performed to ensure structural validity of Yoruba version, and construct validity was investigated with Spearman rank correlation coefficient.

Results

The Yoruba version of DASH has semantic, idiomatic, linguistic and conceptual equivalence with the English DASH. Thirty linear components were identified within the data set. Principal factor analysis of the Yoruba DASH revealed a seven factor scale, having fulfilled all the necessary conditions. The Kaiser-Meyer-Olkin measure of sampling adequacy was 0.61, and Barlett’s test of Sphericity was adequate and significant (χ² (1066) = 435, p = 0.001). Significant correlation (r = 0.994, p = 0.001) exists between scores obtained on English and Yoruba versions of DASH.

Conclusion

A cross-culturally adapted, valid Yoruba version of DASH is available for use in in south western Nigeria and other similar populations.

Keywords

Cross-cultural adaptation outcome measure validity arm disability Nigeria

Introduction

Musculoskeletal disorders (MSDs) are leading causes of long-term disability, with substantial impact on quality of life (QoL) and use of health resources. Overall cost of MSDs was estimated to be about 214.9 billion US dollars, of which 38% was spent on hospital admission and 21% on nursing home care.¹ There is no information on the economic cost of MSDs in Nigeria. The prevalence of MSDs has also been reported among different occupational groups in Nigeria.^2–7 The upper limbs (shoulder, arm, hand and wrist) constitute a large proportion/percentage of the body parts affected by MSDs.⁸ The point prevalence of upper extremity MSDs ranged from 1.6 to 53%, while 12-month prevalence ranged from 2.3 to 41%.⁹ Few studies have investigated the prevalence of upper extremity MSDs in patient populations in Nigeria. These studies are hospital-based. Oyedele et al.¹⁰ reported that 12.75% of patients who attended two major hospitals in Ibadan during a three-month period, presented with hand pain.

The management of MSDs includes pharmacological and non-pharmacological modalities. Physiotherapy, which is often aimed at drawing upon a range of non-pharmacological modalities, plays a significant role in the effective management of MSDs.¹¹ Effective physiotherapy management of MSDs requires the use of outcome measures to evaluate the effectiveness of treatment interventions, monitor patients’ progress, ensure accountability and predict patients’ prognosis.¹² Many outcome measures are used in the assessment of symptoms (impairments), aspects of wellbeing, functioning (disability), general health perceptions, QoL, reports and ratings of healthcare of individuals with MSDs, particularly of the upper limb.¹³ Some of these outcome measures include: the upper extremity functional index,¹⁴ shoulder pain and disability index,¹⁵ Croft disability questionnaire¹⁶ and Disability of the Arm, Shoulder and Hand (DASH) questionnaire.¹⁷ The DASH questionnaire is a valid and reliable instrument that was jointly developed by Institute for Work and Health and the American Academy of Orthopedic Surgeons Outcomes Research Committee in an attempt to develop a uniform outcome measure that reflects the effect of upper extremity diseases and injuries on upper extremity function.¹⁷ It is a region-specific instrument that can be used as either a one-time measure or to monitor change over time.¹⁸ Furthermore, the DASH has been shown to be reliable and valid in patient populations with upper extremity disorders.^19,20 It is, thus, a standardized instrument in assessing the level of disability among individuals with upper extremity MSDs and will be very relevant in a population like Nigeria, which has a high prevalence of MSDs.

To the best of our knowledge, there is no existing upper extremity outcome measure that has been developed or cross-culturally adapted for use in Nigeria. Our choice of DASH was based on its wide utility globally, region specificity for use in all upper extremity disorders and on the short period (between 8 and 10 min) for its completion especially in a busy clinical environment.^21–24 For measures to be used across cultures, the items must not only be translated well linguistically but also adapted culturally in order to maintain the content validity of the instrument across different cultures.²⁵ The familiarization and utilization of outcome measures by physiotherapists in Nigeria are low.²⁶ We decided to translate and cross-culturally adapt the DASH into Yoruba, a major Nigerian language (spoken by over 40 million people in southwest Nigeria) in order to facilitate the utilization of outcome measures in the Nigerian clinical environment and other similar populations in Africa. We also tested the initial construct validity of the Yoruba version using the description by Schellingerhout et al.,²⁶ in their systematic review on measurement properties of translated versions of neck-specific questionnaires. They described construct validity in three aspects of cross-cultural validity, structural validity and hypothesis testing.

Purpose of the study

This study was an initial step to cross-culturally adapt DASH into a Nigerian language, specifically Yoruba language, which is the predominant language in south west Nigeria and investigate its structural and construct validity.

Methods

This study’s protocol was approved by the University of Ibadan/University College Hospital research and ethics committee Ibadan, Nigeria (UI/EC/13/0144). The study was in two phases vis-à-vis cross-cultural adaptation phase and validity testing phase.

Cross-cultural adaptation phase

Approval to cross-culturally adapt English DASH into Yoruba language was obtained from the developers of DASH (Institute of Work and Health and American Academy of Orthopedic Surgeon). We followed the guidelines for cross-cultural adaptation by developers.²⁵ The steps involved in the adaptation process were: (i) forward translation of the English DASH into Yoruba language; (ii) synthesis of the Yoruba translations; (iii) backward translation of the synthesized Yoruba version into English; (iv) expert committee meeting to produce a pre-final Yoruba version; (v) pretesting among target population and (vi) expert committee meeting to produce final version.

Forward translation

The translation process involved two bilingual translators with different profiles and background. One translator was informed of the concepts being examined in the questionnaire, while the other translator was not aware or informed of the concepts being examined and was neither from a medical background nor working in a medical institution. The translators were requested to produce a written report of the translation they completed highlighting challenging phrases and uncertainties. They also summarized their rationale for their choice of words.

Synthesis

The two translators met to synthesize the results of the translations with a recording researcher. The synthesized translation was used for back translations.

Backward translation

Two independent translators who were totally blinded to the original process of translation translated the questionnaire back to English language hence producing two English versions.

Experts’ committee meeting

The members of the expert committee comprised four bilingual linguists, a methodologist, a physiotherapy clinician and a language expert who have published in the area of validation study and involved in translation studies. They were given copies of the English DASH, the two forward translations, the synthesized Yoruba translation and the two back translations together with corresponding written reports on the rationale for each decision at earlier stages. The committee reviewed and consolidated all the translations of the questionnaire and reached a consensus on any identified discrepancy. All the items (word by word) were assessed for conceptual, linguistic, semantic and idiomatic equivalence. This was to ensure the content validity of the Yoruba version and adequate comparison of it to the original DASH. Minutes of the expert panel meeting was also taken by one of the authors. The Pre-final Yoruba Version (PYV) of the questionnaire was produced by the panel of experts for pretesting.

Pretesting

The PYV was tested among 30 individuals with upper extremity MSDs, whose mother tongue is Yoruba and who were attending outpatient physiotherapy clinic of a tertiary health institution. Information on part(s) of the upper extremity affected and participants’ socio-demographic characteristics (age, sex, marital status and occupation) were obtained from the participants. Each patient was given the PYV, and a pretest questionnaire (also translated in Yoruba) was attached to it for debriefing. The pretest questionnaire sought to find out from the participants, if there was any ambiguity or lack of comprehension of any item in the translated Yoruba DASH Questionnaire.

Experts’ committee meeting

All the members of the expert committee considered the findings from the pretesting in order to produce the final Yoruba version of DASH (DASH-Y).

Validity testing phase

The participants for this study were 52 individuals with upper extremity MSDs who were newly referred for physiotherapy treatment in selected public hospitals in Ibadan. Written and verbal informed consent was obtained from participants. Participants were included in the study if they were aged 18 years and above, literate in both English and Yoruba languages and able to complete the questionnaire in both languages. The Yoruba speakers were those whose mother tongue is Yoruba. Participants with upper MSDs originating from neurological disorders or tumors were excluded. Information on part(s) of the upper extremity affected and socio-demographic characteristics (age, sex, marital status and occupation) were obtained from all participants. Copies of the DASH questionnaire were hand distributed to individuals with disability of the upper extremity for self-administration. Participants were asked to answer all sections, respond based on their ability to perform activities over the past week and give only one answer per question. No more than three items can be left unanswered to accurately calculate the score on the DASH. Each item on DASH has five response choices, ranging from ‘no difficulty or no symptom to unable to perform activity or very severe symptom’, and is scored on a 1 to 5 point scale. The scores for all items were then used to calculate a scale score ranging from 0 (no disability) to 100 (most severe disability). In order to assess the construct validity of DASH-Y, all the participants self-completed both English DASH and DASH-Y on the first visit during which they were assessed for treatment. Structural validity was also investigated based on the data obtained from the 52 participants.

Data analysis

Data analysis was done using SPSS version 20. Socio-demographic variables were summarized with percentages. Spearman correlation (r) was used to assess the correlation between the scores on the English and DASH-Y. Alpha level was set at 0.05. The structural validity of DASH-Y was investigated using factor analysis. Principal component analysis was used to extract factors. Independent factors were obtained using the Varimax rotation method.

Results

Translation

During the synthesis of the forward translations, due to the socio-cultural issues and for simplification purpose, item 1 (open a tight jar), item 7 (do heavy household chores (e.g. wash walls, wash floors), item 11 (carry an object (over 10 lbs)), item 18 (recreational activities in which you take some force … (e.g. golf, etc.)) and item 19 (recreational activities in which you move your arm freely (e.g. playing Frisbee, etc.)) were modified (Table 1). In the Nigerian context, a tight jar is not commonly used in our environment and not explanatory enough for a lay person, hence the item was modified as ‘open a well corked bottle’. Washing of walls is an activity that is not often performed by most Nigerians hence the phrase ‘wash wall’ was replaced with ‘fetching from the well’ which was considered as a heavy household chore that is commonly performed in the Nigerian environment. The unit of weight used in item 11 was considered not to be easily understood by an average Nigerian hence a 4 L gallon filled with water which appears equivalent to a weight of over 10 lbs was used. The word ‘golf’ is not friendly in the Nigerian culture hence an activity (Long tennis) that depicts the force or impact through the upper limb was used. Playing Frisbee was modified with activities that connote free movement of the arm. A synthesized forward translation of DASH into Yoruba was thereafter produced. During the expert committee meeting, there were discrepancies on item 1 (open a tight jar), item 5 (push open a heavy door), item 8 (garden or do yard work), item 15 (put on a pullover sweater) and item 26 (tingling (pins and needles) in your arm, shoulder or hand) which were resolved. The discrepancies included: item 1 (open a tight jar) ‘Si ideri agolo ti a de pa’. Agolo in this context is a tin that does not require maximum use of the hand. Item 5 (push open a heavy door) ‘Si ìlèkùn to gbopon’ does not correspond with the initial English word ‘push open a heavy door’. Item 8 (garden or do yard work) ‘Títúnàyíká, è $.$ yìnkùlé tàbí itagbangba $s .$ e’ only explains tidying the surroundings rather than also including gardening. Item 15 (put on a pullover sweater) ‘Wíw $o .$ a $s .$ $o .$ àwò $.$ lè $.$ kèamóoru-múni/amúni-làágùn’ cannot be interpreted by a lay person as pullover, the translation sounds complex. Item 26 (tingling (pins and needles) in your arm, shoulder or hand) ‘Gigunni bí abere ni apá, èjìká tàbí owó re’ only explains the pins and needle without the inclusion of sensation and feeling. These discrepancies and their resolutions are presented in Table 2. Following the resolutions, a consensus was reached, and a pre-final version was arrived at and used for pretesting.

Table 1.

Discrepancies identified and resolution to produce a synthesized version of the forward translations.

Discrepancies	Resolution
1. Open a tight jar, in this context, a tight jar is not commonly used in our environment and not explanatory enough for a lay man.	A well corked bottle was used because, it is quite explanatory to a lay man.
7. Do a heavy household chore (e.g. wash walls, wash floors): the discrepancy here is the washing of walls, in the Nigerian environment, people do not consider washing the wall as a common household chore for an average Nigerian.	Rather than using the context ‘wash wall’, fetching water from the well was used because it is a heavy household chore involving the shoulders and arms and commonly carried out in the Nigerian environment. The word ‘heavy’ was central to the resolution for the replacement. Some common household tasks such as cleaning windows, sweeping the floor will not connote a heavy task in the Nigerian culture. Fetching water from the well entails the heavy task of drawing water from the well.
11. Carry an object (over10 lbs), an example worth over 10 lbs was needed for easy understanding.	A four litre of gallon filled with water was used, which is also synonymous to a weight of over10 lbs.
18. Recreational activities in which you take some force or impact through your arm, shoulder or hand (e.g. golf, hammering, tennis, etc.).	The example of the word ‘golf’ is not friendly in the Nigerian culture, hence an activity that depicts the force or impact through the upper limb was used.
19. Recreational activities in which you move your arm freely (e.g. playing Frisbee, badminton, etc.).	Playing Frisbee is an uncommon activity in Nigeria, hence an activity that depicted free movement of the arm was used.

Table 2.

Identified discrepancies on the synthesized version (T12) and their resolution.

Discrepancy	Resolution (consensus)
1. Si ideri agolo ti a de pa. The ‘agolo’ in this context is a tin that does not require the maximum use of the hand. An object can be used to open the tin that was used in this context.	S $.$ í ìdérí ìgò bótù tí a dé pa was suggested and concluded on because it requires mobility of the hand.
5. Si ìlèkùn to gbopon. This is translated in English as ‘open a heavy door’, which does not correspond with the initial English word ‘Push a heavy door’.	‘Fi owó taari ìlèkùn to gbopon si’ was concluded on because it explains the word ‘push’.
8. ‘Títún àyíká, è $.$ yìnkùlé tàbí ita gbangba s $.$ e’ only explains tidying the surroundings rather than also including gardening.	‘Se isé oko nínú àgbàlá re’ was suggested and concluded on because it describes the actual meaning of the word ‘Garden or do yard work’.
15. ‘Wíwo $.$ as $.$ o $.$ àwò $.$ lé $.$ kè amóoru-múni/amúni-làágùn’ cannot be interpreted by a lay man as pullover. The translation sounds complex.	‘Wo $.$ as $.$ o $.$ òtútù alatorunwo’ was suggested and agreed on because it is explanatory enough to all participants.
26. ‘Gigunni bí abere ni apá, èjìká tàbí owó re’ only explains the pins and needles without the inclusion of sensation and feeling.	‘Níní ìmòlára gígún ni bí abé $.$ ré $.$ ní apá, èjìká tàbí o $.$ wó $.$ rè $.$ ’ was suggested and agreed on because ‘nini ìmòlára’ is a feeling or sensation.

Findings from debriefing interview

Thirty participants (18 males, 12 females) with disability of the upper extremity participated in the pretesting phase. The items in the pre-final Yoruba version of the DASH questionnaire were well understood by the participants. All of them confirmed that all the items were relevant to individuals with disability of the upper extremity. They all reported that there were no ambiguous or double-barreled words (Table 3). There were no issues of ambiguity. Only one item was not understood by a participant because the Yoruba sign used for a word was missing. This was included and this item was later understood by the participant. According to the recommendations of the developers of DASH, an item can only be replaced or modified if there are complaints from more than one participant during the pretesting hence the item was retained in the final version. However, six male participants reported that items 4 and 7 were not applicable to them. Three female participants also reported that they do not get involved in sporting activities and as such items 18 and 19 were not applicable to them. All the participants agreed that all the activities were relevant to individuals with disability of the upper limb. Following the findings from the debriefing interview and pretesting, the expert committee agreed all the items be retained in the final version; hence, the final version of Yoruba DASH was produced. Following the guidelines provided by the developers of DASH, final approval for the publication of the Yoruba DASH was given. The Yoruba version can be accessed at http://www.dash.iwh.on.ca.

Table 3.

Pretesting of Yoruba translation of DASH.

Section	Yes	No
1. Introduction
Is it easy to understand?	30	0
Does it clearly indicate the purpose of the study?	30	0
Are the response options easy to apply	30	0
2. Overall layout
Does the size of each letter make for easy reading?	30	0
Are the pages numbered clearly and stapled securely?	30	0
3. Main body of questionnaire
Is there any word you did not under stand in any of the questions?	1	29
Is the questionnaire of an appropriate length?	30	0
Are any questions unnecessary or irrelevant?	30^a	0
Is there any word that has more than one meaning to you?	0	30
Is there any question that is asking more than one question?	0	30
The total number of people that participated in the pretesting of the questionnaire was 30

Six males and three females reported that although all the items were relevant to individuals with disability of the upper extremity, some items (items 4 and 7 for the males and items 18 and 19 for the female) were not often applicable to them.

Structural validity (factor analysis)

Table 4 shows the communalities of all the 30 items on DASH-Y after extraction. All the items correlated at least 0.6 with at least one other item on the scale. The preliminary analysis of the DASH-Y revealed the Kaiser-Meyer-Olkin (KMO) measure of sampling adequacy with the Chi square result and Barlett’s test of Sphericity were adequate (0.6, χ² (1066) = 435, p = 0.001). Tables 5 and 6 show the principal component analysis; before extraction there were 30 items, 30 linear components were identified within the data set. Seven factors with eigenvalues > 1 were extracted from the 30 items. Table 5 reveals the component matrix of the variables before rotation. The matrix contains the loading of each variable on each factor. Figure 1 shows when the scree plot began to tail-off after the seventh factor before a stable plateau was reached.

Figure 1.

Scree plot of items on DASH-Y.

Table 4.

Communalities of items on DASH-Y.

Item	Initial	Extraction
1	1.000	0.77
2	1.000	0.82
3	1.000	0.82
4	1.000	0.75
5	1.000	0.60
6	1.000	0.77
7	1.000	0.77
8	1.000	0.71
9	1.000	0.77
10	1.000	0.60
11	1.000	0.76
12	1.000	0.77
13	1.000	0.85
14	1.000	0.67
15	1.000	0.68
16	1.000	0.76
17	1.000	0.60
18	1.000	0.65
19	1.000	0.46
21	1.000	0.73
22	1.000	0.65
23	1.000	0.73
24	1.000	0.75
25	1.000	0.63
26	1.000	0.80
27	1.000	0.70
28	1.000	0.78
29	1.000	0.70
30	1.000	0.74

Table 5.

Component matrix of the items on DASH-Y.

Item	Component
Item	1	2	3	4	5	6	7
1	.803
2	.752
3	.716
4	.681
5	.674
6	.666
7	.647	−.412
8	.632					.403
9	.631				−.443
10	.626
11	.603	.476
12	.586
13	.556
14	.555			−.541
15	.515		.457
16	.421
17	.404	.680
18		.671
19		−.655
20	.414	−.642
21	.455		−.610
22	.503		−.521
23			.513	.451
24			−.510
25	.515			−.644
26		−.479		.523
27						.453
28	.424	−.410				.439
29							−.510
30

Table 6.

Varimax rotated component matrix of items on DASH-Y.

Item	Component
Item	1	2	3	4	5	6	7
1	.870
2	.789
3	.786
4	.661
5	.492		.425	.404
6
7		.778
8		.678
9		.658		.460
10		.610
11	.469	.532
12			.841
13			.726
14			.695
15			.597			.437
16			.489		.410
17				.815
18				.783
19			.464	.542
20				.485			.409
21				.440
22					.850
23			.411		.642
24					.483
25						.709
26	.596					.633
27		.480				.632
28		.422				.621
29							−.717
30							.678

Before Varimax rotation, factor 1 had 21 items, while the other nine items were distributed within the other six factors (Table 5). After Varimax rotation, the items were better distributed within the seven factors. Factor 1 had a reduction from 21 items to 7 items (Table 6). The seven factors with eigenvalues > 1 explained 71.6% of the variance (Tables 7 and 8). Before rotation, the first factor accounted for 28.8% of the variance, and factors 2, 3, 4, 5, 6 and 7 accounted for 13.4%, 7.7%, 7.4%, 5.6%, 4.8% and 3.9% of the variance, respectively (Table 7). Varimax rotation showed that the first factor comprises seven items of activities of fine movements. The second factor comprises six items that relate with ability to dress, third factor comprises five items that relate to issues of functional ability, fourth factor comprises four items that deal with activities of daily living (chores), factor 5 comprises two items that deal with recreational activities, factor 6 comprises four items that deal with work activities while factor 7 comprises two items that relate to sexual activities. Table 8 shows the value of the rotated factor matrix in factor analysis which is a matrix of the factor loadings for each factor. This matrix contains the same information as the component matrix in Table 7 except that it is calculated after rotation. The first factor now accounted for 13.3% of the variance, and factors 2, 3, 4, 5, 6 and 7 accounted for 12.1%, 11.8%, 11.1%, 9.1%, 8.7% and 5.6% of the variance, respectively (Table 8).

Table 7.

Factor analysis without Varimax rotation of the DASH-Y.

Factor	Eigenvalues	%Variance	Cumulative%
F1	8.7	28.8	28.8
F2	4.0	13.4	42.2
F3	2.3	7.7	49.9
F4	2.2	7.4	57.3
F5	1.7	5.6	62.9
F6	1.4	4.8	67.7
F7	1.2	3.9	71.6

Table 8.

Factor analysis and Varimax rotation of the DASH-Y.

Factor	Eigenvalues	%Variance	Cumulative%
F1	4.0	13.3	13.3
F2	3.6	12.1	25.4
F3	3.5	11.8	37.2
F4	3.3	11.1	48.2
F5	2.7	9.1	57.3
F6	2.6	8.7	66.0
F7	1.7	5.6	71.6

Construct validity

Participants were 28 (53.8%) males and 24 (46.2%) females aged 43.33 ± 12.59 years. Twenty-eight participants (53.8%) were self-employed. Forty (76.9%) participants were married. None of the participants recorded the minimum disability score of 0 and maximum disability score of 100 on the DASH-Y, representing the maximum health status score (ceiling) and the minimum health status score (floor), respectively. There was a significant correlation between the scores obtained on the English DASH and DASH-Y (r = 0.994 (p ≤ 0.001).

Discussion

This study is the first on translation and cross-cultural adaptation of DASH into any Nigerian language. Our results strongly indicate that the DASH-Y can be used for evaluating upper extremity MSDs among patients in Southwest Nigeria and other Yoruba speaking populations in West Africa. In forward translation of the DASH Questionnaire into Yoruba language, some examples on recreational activities in items 18 (golf) and 19 (Frisbee) are activities an average Nigerian is not familiar with. These activities are not culture-friendly in the Nigerian context. These observations are similar to those of Tongprasent et al.²⁴ in their study on cross-cultural adaptation of the DASH questionnaire in Thai. They reported that playing Frisbee was unrelated to the Thai culture. In this study, all English words and activities that were unfamiliar to the Nigerian environment were substituted with Yoruba words that are more appropriate in the context and that maintain semantic equivalence as the English words in the Yoruba version of DASH. Also, some English words had equivalent words in Yoruba language but had to be used as ‘loaned’ or ‘borrowed’ words, such words included bed as‘bé $.$ è $.$ dì’and bulb as ‘bó $.$ ò $.$ bù’. It is important to note that the modifications did not alter the meanings of the words in English DASH. The conceptual equivalence of the words was retained.

During the synthesis, the words that were replaced were in consonance with the process of cross-cultural translation of scales. In the cross-cultural adaptation process, items must connote the cultural inclinations of the target population. In this study, washing of walls is not commonly done in our culture (Yoruba); however, fetching of water from the well is a task as heavy as washing the wall; therefore, it was used to replace washing of the wall. All items of the DASH were understood by the respondents during the pretesting of the pre-final Yoruba version of the DASH and the debriefing interview. Some male participants reported that items on household chores were not applicable to them; this is not surprising viewing from the cultural perspective where most Yoruba men do not often get involved in food preparation or doing household chores. Similarly, females do not get involved in sporting activities as the society and culture see them as mothers who have to be responsible for family needs rather than participating in such sports.

Previous studies on the cross-cultural adaptation of DASH provided information on the time it took for the completion of the adapted versions^21–24; however, we did not take cognizance of the time for completion in this study. This is essentially important when the adapted versions are to be used in a busy clinical environment. Future studies on cross-cultural adaptation of DASH into other Nigerian languages should take note of the time taken to complete the adapted versions. According to Beaton et al.,²⁵ if two or more participants complained or made any addition, there is need for revision. In our study, since there was no question of ambiguity and use of double-barreled words from any of the participants, there was no need for revision as the participants understood all the items on DASH-Y.²⁷

Factor analysis according to Nunnally²⁸ quoted in Matsunaga²⁹ is ‘intimately involved with the question of validity and it is at the heart of the measurement of psychological constructs’. In other words, factor analysis provides a diagnostic tool to evaluate whether the collected data are in line with the theoretically expected pattern, or structure of the target construct and thereby determine if the measures used have indeed measured what they are purported to measure. The choice of principal component analysis was informed by the fact that the scale had already been established on an existing theory by the original authors of the English version, and there is no need for the exploratory factor analysis.^30–32 Kaiser³³ recommends accepting values of KMO greater than 0.5 as acceptable. Values below this should lead to either collection of more data or a rethink of which variables to include. The Barlett’s test of Sphericity revealed that p = 0.0001, a significant test that indicates that the rotation matrix is not an identity matrix; therefore, there are some relationships between the variables. For these data, the Barlett’s test is highly significant (p = 0.0001), and therefore factor analysis is appropriate.

The factorability of the 30 items on DASH-Y was investigated, and this revealed that all the items correlated at 0.5 and above with at least one other item on the scale. This suggests reasonable factorability.³⁴ The Kaiser-Meyer-Olkin measure of sampling adequacy was 0.61, which is above the recommended value of 0.6, and Bartlett’s test of sphericity was significant (χ² (1066) = 435, p = 0.001).³¹ The communalities were all above 0.5, thus confirming that each item shared some common variance with other items and be retained on the DASH-Y. Given these overall indicators, factor analysis was conducted on all the 30 items of the DASH-Y. This is in consonance with the findings of Veehof et al.,³⁵ Imaeda et al.,³⁶ Lee et al.³⁷ and Fayad et al.³⁸ in their studies on the Dutch, Japanese, Chinese and French versions of DASH, respectively. The component matrix of the variables before rotation in this present study revealed that the matrix contains the loading of each variable on each factor. However, all loadings below 0.4 were suppressed in the output. At this stage, seven factors have been extracted by Kaiser’s criterion, and the scree plot began to tail-off after seven factors before a stable plateau is reached. The rotated factor matrix shows that the question that loads highly on each factor helps us to identify what the construct might be helping to identify common themes. All items retained in each factor have a high loading (>0.5) in each of the factors. The loading of 21 items was over 0.6. These findings further validate the relevance of all the items on the DASH-Y. There could be seven themes in the Yoruba DASH. The unidimensional factor structure of the English DASH is challenged from our findings and those of Lehman et al.,³⁹ Forget et al.⁴⁰ and Novac.⁴¹ Lehman et al.³⁹ using both exploratory and confirmatory factor analyses reported a three factor model of the English DASH. They concluded that more research was needed to enhance the interpretability of DASH. Forget et al.⁴⁰ in their study on psychometric evaluation of DASH in a population with Duputyren’s contracture also reported that the items loaded on four factors though with one factor accounted for 60% of the variance. In our study, only one factor accounted for 29% before rotation. We presume that the cultural context of some items of the DASH-Y could have contributed to the seven dimension factor structure of the DASH-Y. Another plausible reason for this is the diversity of the patients with single or multiple upper extremity disorders of the upper limb whether at a point in time or many points in time. Our intention was not to categorize the patients into specific or multiple disorders; hence, it is possible that some patients could have distal disorders, while others had proximal disorders of the upper extremity. In cross-cultural adaptation of the DASH, it is important that the factor analyses of each adapted version should be explored. The implication is that the multi-factor domains should be considered when utilizing the DASH as a single construct score of upper extremity disability.⁴¹ The loading on factor 1 seems to relate to difficulty with fine movements of the hands, factor 2 relates with ability to dress, factor 3 relates to issues of functional ability, factor 4 deals with activities of daily living (chores), factor 5 deals with recreational activities while factor 7 relates with sexual activities. Since the DASH has to do with assessing disabilities of the shoulder, arm and hand, the sub themes show that it actually can measure what it is set out to measure and that it has seven domains within the 30 items.

The results obtained in this study showed that there was a significant correlation (p < 0.001) between the scores obtained on the English and Yoruba versions of DASH. This could also confirm that the linguistic equivalence of the Yoruba DASH was achieved during the cross-cultural adaptation process. To the best of our knowledge, no upper extremity outcome measure has been cross-culturally adapted or translated into any Nigerian language; hence, we can only discuss our findings based on studies conducted in other populations different from the Nigerian population. This correlation is similar to the study carried out by Fayad et al.³⁸ in the validation of French version of DASH with a correlation coefficient of 0.78 having good construct validity. A strong validity was thus indicated by the observed correlation (r = 0.994), which suggests that the Yoruba version of DASH is a valid translation of the English version. The Y-DASH is therefore a valid instrument for Yoruba-speaking patients with upper extremity musculoskeletal disability.

Translation of the DASH questionnaire into other major Nigerian Languages should be done with evidence of their psychometric properties provided in order to enhance its utility across various cultures in the country.

Limitations of the study

The scope of measurement properties assessed for DASH-Y is limited. Further testing of measurement properties such as reliability, responsiveness was not determined in this study. Another limitation is the small sample involved in the factor analysis of DASH-Y.

Conclusions

A Yoruba culturally adapted version of DASH (DASH-Y) is available for use in the Yoruba speaking population of Nigeria and in other similar populations. This finding is an initial attempt at providing the content relevance, content coverage and initial validation of DASH-Y. The strength of this study lies in the rigorous and demanding process of cross-cultural adaptation as required by the developers of DASH using the guidelines recommended by Beaton et al.²⁵ The Yoruba version of DASH can be accessed at http://www.dash.iwh.on.ca.

Footnotes

Acknowledgement

The authors acknowledge the input of all members of the expert panel (particularly Dr. B.O.A. Adegoke) for their thoroughness in following the recommended guidelines.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

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