Development and evaluation of the Automotive ...

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International Journal of Industrial Ergonomics 36 (2006) 141–149 www.elsevier.com/locate/ergon

Development and evaluation of the Automotive Seating Discomfort Questionnaire (ASDQ) Dannion R. Smitha, David M. Andrewsb,, Peter T. Wawrowa a

Ergonomics Department, Schukra of North America, 360 Silver Creek Industrial Dr., R.R. #1 Tecumseh, Lakeshore, Ont., Canada N8N 4Y3 b Department of Kinesiology, 401 Sunset Ave, University of Windsor, Windsor, Ont., Canada N9B 3P4 Received 29 August 2005; accepted 29 September 2005 Available online 28 November 2005

Abstract The purpose of this study was to develop and evaluate an assessment tool capable of quantifying subjective occupant discomfort in automotive seating. To date, the majority of questionnaires present in the automotive seating industry have been designed using questionable developmental methods with suspect statistical rigor. The Automotive Seating Discomfort Questionnaire (ASDQ) was developed with statistically significant levels of readability, scale reliability, and face validity, using proven methods for questionnaire development. Methods included key informant interviews, several pilot tests, and an experimental assessment that involved the subjective evaluation of 3 identical front driver-side seats in 5 different seat positions over 3 sessions. The ASDQ was administered along side an established automotive seating questionnaire to showcase increases in performance through differences in methodologies, scale usage, and variable content. The ASDQ was shown to possess significant levels of reliability (po0:05) and internal consistency. A between questionnaire comparison revealed significantly correlated subject responses (R2 ¼ 0:715), as well as significant differences between similar questionnaire variables. The choice of measurement scale, increased variable content, establishment of face validity, and thorough experimental methods resulted in the ASDQ measuring the construct of automotive seating discomfort in a more comprehensive manner then previously developed industry questionnaires. It was concluded that the ASDQ reliably and repeatedly measures the construct of automotive seating discomfort, contains face validity, has established a foundation for construct and content validity development, and provides a comprehensive objective measure of occupant discomfort in automotive seating. Relevance to industry This study provides a rigorous questionnaire development process for the automotive seating industry. The resultant questionnaire can be used in the evaluation of automotive seat designs. r 2005 Elsevier B.V. All rights reserved. Keywords: Automotive seating; Discomfort; Questionnaire; Visual analog scale

1. Introduction An automotive seat represents a work environment which must optimally position the occupant to perform the task of driving, meet various safety requirements, and be acceptable to the driver’s comfort needs. It is this last point that is the most difficult to measure and satisfy, but is regarded as the main criteria by which seats are judged. Corresponding author. Tel.: +1 519 253 3000x2433; fax: +1 519 973 7056. E-mail address: [email protected] (D.M. Andrews).

0169-8141/$ - see front matter r 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.ergon.2005.09.005

Thus, automotive seat development is an iterative process resulting in several prototype builds, with each build followed by a subjective evaluation of seat comfort (Kolich, 2004). In the automotive seating industry the goal is to have seats that are more comfortable than competitive seats. However, comfort is a subjective construct that is difficult to interpret, measure, and specifically define due to its psychophysical nature (Shen and Parsons, 1997). This ambiguity is reflected in Random House Webster’s College Dictionary definition: ‘‘relief in affliction’’ and ‘‘a state of ease and satisfaction of bodily wants, with freedom from

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D.R. Smith et al. / International Journal of Industrial Ergonomics 36 (2006) 141–149

pain and anxiety’’ (Steinmetz, 1997). Measuring gradations of comfort is a difficult task since once a feeling of relief or satisfaction has been attained, providing a feeling of more contentment is intangible. In contrast, discomfort is a construct that is proposed to lie on the opposite end of a continuum and is thought to be easier for subjects to identify a degree of affliction. Supporting this assumption, numerous studies have chosen to explore occupant discomfort (i.e. Crane et al., 2004; El Falou et al., 2003; Kolich, 2000; Porter et al., 2003; Reed et al., 1991; Shen and Parsons, 1997). Given this wide body of supporting literature, discomfort has taken on numerous definitions, including that of Shen and Parsons (1997) as ‘‘a generic and subjective sensation that arises when human and physiological homeostasis, psychological well-being, or both, are negatively affected’’ and by Steinmetz (1997) as ‘‘an absence of comfort or ease; hardship or mild pain’’. This hardship or mild pain can be more readily identified, providing seat developers a target to eliminate that should translate into a more comfortable seat. Thus, the current challenge is to determine how physical seat properties and occupant perceptions contribute to the construct of discomfort. Items specific to the internal physical components of the seat have been identified through available anthropometric seat component data (i.e. thigh, buttocks), objective design standards (i.e. seat length, seat width), and recent related literature. This has resulted in 30 internal discomfort source items related to seating and formed the basis for questionnaire content (Table 1) (Giacomin and Quattrocolo, 1997; Goonetilleke and Feizhou, 2001; Gyi and Porter, 1999; Kolich, 2004; Kolich, 2000; Reed et al., 1991, 1994). The analysis of recent related literature also identified 3 key external factors known to contribute to occupant seating discomfort: seating duration, hand reach, and vibration (Blair et al., 1998; Jung and Choe, 1996; Reed and Massie, 1996). Reed and Massie (1996) showed that 82.5% of comfort score variance was accounted for after being seated for 20 min. Jung and Choe (1996) showed that inclusion of proper arm postures influence shoulder and hip position, forcing the subject to inadvertently assume different postures, which ultimately increases the realism of the simulation. Vibration has been shown to interact with discomfort on a continuum (Dhingra et al., 2003). Thus, when vibration levels are low, discomfort evaluations are dominated by physical seat characteristics and the effects of vibration are negated (Dhingra et al., 2003). These external factors must be controlled during questionnaire evaluation, in accordance with the reviewed literature, to increase experimental trial realism and overall questionnaire significance. Seat evaluation methods include ride-and-drive trials, where subjective evaluations are performed in a vehicle while driving, and/or seating buck simulations where the driving experience is recreated in a static setting (El Falou et al., 2003; Kolich, 2000, 2003; Shen and Parsons, 1997;

Table 1 Seating Discomfort Source Items by Questionnaire Iteration Initial

Intermediate

Final

Cushion width Cushion length Cushion firmness Side cushion support Mid cushion support Side cushion comfort Mid cushion comfort Cushion contour Cushion aesthetics Cushion pressure Trim comfort Trim touch Trim aesthetics Trim pressure Backrest height Backrest width Backrest firmness Side backrest support Mid backrest support Side backrest comfort Mid backrest comfort Backrest contour Backrest aesthetics Backrest pressure Lumbar stiffness Lumbar prominence Lumbar comfort Lumbar location Lumbar pressure Overall discomfort

Cushion width Cushion length Cushion firmness Cushion bolsters Cushion center Cushion contour Cushion aesthetics Cushion pressure Trim Trim friction Trim feel Trim aesthetics Backrest height Backrest width Backrest firmness Backrest bolsters Backrest middle Backrest contour Backrest aesthetics Backrest pressure Lumbar stiffness Lumbar prominence Lumbar support Lumbar height Lumbar pressure Overall discomfort

Cushion width Cushion length Cushion firmness Cushion bolsters Cushion center Cushion contour Trim Trim friction Trim feel Backrest height Backrest width Backrest firmness Backrest bolsters Backrest contour Lumbar stiffness Lumbar prominence Lumbar support Lumbar height Lumbar pressure Overall discomfort

In bold: reworded/incorporated into a new source item label. In italics: deleted item. Initial: thirty source items identified from a thorough review of literature. Intermediate: the resultant source items after initial key informant and pilot testing. Final: the final 20 source items with significantly associated questions and wording within the Automotive Seating Discomfort Questionnaire (ASDQ).

Reed and Massie, 1996; Reed et al., 1994). Subjective ratings are collected mainly by questionnaires and/or verbal interviews. Numerous questionnaires are currently available to rate automotive seating comfort, however supporting evidence states most were created without research scrutiny and/or proper research design (Crane et al., 2004; Kolich, 2004; Kolich and Taboun, 2004). To date, the automotive seating industry does not have a gold standard questionnaire with which to measure the construct of seating comfort (Kolich and Taboun, 2004). Although a gold standard does not currently exist in the industry, the Automobile Seat Comfort Survey (Kolich, 2000) is the most established questionnaire in automotive seating literature. The Automobile Seat Comfort Survey (Kolich, 2000) has been shown to be a reliable tool in providing numeric ratings of occupant seating comfort. However, scale selection, variable omission, seat selection, and subject size used during the development of this questionnaire warrant further consideration. Following

ARTICLE IN PRESS D.R. Smith et al. / International Journal of Industrial Ergonomics 36 (2006) 141–149

that discomfort is continuous and should be measured on a continuum, a 7-point Likert scale, as used in the Automobile Seat Comfort Survey (Kolich, 2000), is unfavourable due to the intermediate anchors, implying that discomfort is a divisible construct and not continuous. However, this questionnaire has been used in Kolich (2000, 2003, 2004), and Kolich and Taboun, (2004) all returning significant results. Outside of the automotive industry the Quality of Health Care in Inflammatory Bowel Disease (QUOTE-IBD) questionnaire developed by van der Eijk et al. (2001) possesses a strong methodological background and statistically significant reliability and validity. Beyond the parallel of questionnaire development, the QUOTE-IBD is applicable to seating discomfort due to its use of a visual analog scale (VAS) to rate pain. VAS is a direct estimation method scale that is designed to elicit from a subject a direct quantitative estimate concerning the magnitude of an attribute (Streiner and Norman, 2003). This is accomplished by using a line of fixed length, usually 10 cm, with anchors located at the extreme ends and no words describing the intermediate positions (Streiner and Norman, 2003). This provides a continuum on which subject responses can be placed. As previously defined, the construct of discomfort encompasses both pain and psychological well-being. Thus, using a VAS, which is known to provide accurate quantitative estimates of both attributes, is optimal for evaluating automotive seating discomfort. The aims of the current study were to develop a questionnaire that has an acceptable level of readability as defined by a Flesch–Kincaid readability score, statistically significant (0:3opo0:8) questions containing key source items, and face validity as defined in Streiner and Norman (2003). Ideally, the questionnaire should have high levels of scale repeatability and contain reliable and internally consistent sub-scales. It is hypothesized that the established questionnaire will provide reliable estimates of discomfort between and within gender, day, and seat position factors. Ultimately, the developed questionnaire will measure the construct of seating discomfort with a level of detail that is currently lacking in the automotive seating industry, utilizing aspects of several established questionnaires in the literature. 2. Methods 2.1. Development of the automotive seating discomfort questionnaire (ASDQ) 2.1.1. Key informant interviews Thirty source items identified in the review of literature (Table 1) were tested using a key informant interview process as defined in Streiner and Norman (2003). These interviews consisted of product designers, project managers and engineers, an ergonomic specialist, and sales representatives, all familiar with the automotive seating industry.

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This served to omit ambiguous, jargon filled, and/or double-barreled questions existing in the questionnaire as well as to select an aesthetically pleasing layout. Flesch– Kincaid grade level readability tests were performed on all iterations of the ASDQ to ensure an appropriate level of readability (between grades 7 and 8). 2.1.2. Pilot testing Several pilot tests were performed in order to improve statistical significance and decrease error contained within the ASDQ. This process assisted in ensuring that appropriate levels of questionnaire readability, wording, aesthetics, and statistical significance of both question variable and resultant data was achieved and maintained in parallel with questionnaire modification. Three pilot tests were conducted. Pilot test #1 (N ¼ 11) consisted of volunteers using the ASDQ to evaluate a car seat in situ, as well as providing verbal feedback. Corresponding changes were made to improve question wording and levels of statistical significance. Pilot test #2, which was conducted with the same subjects (N ¼ 11) and seat/vehicle as pilot test #1, resulted in further revisions (sentence length, wording, and layout changes) to the ASDQ. Pilot test #3 (N ¼ 15) used a portion of the subject pool from the previous pilot tests as well as additional volunteers. A test/retest evaluation of a single seat was conducted with a separation period of 24 h. A factor analysis was conducted for questionnaire sub-scale identification. Specifically, a principal component analysis was used to show cumulative variance which established the number of sub-scales present as well as identifying both the main sub-scales and those variables associated within each identified sub-scale. Sub-scale internal consistency was calculated using a correlation method with resultant Cronbach’s a values establishing significance (a40:7). 2.2. Establishing the ASDQ—experimental trials 2.2.1. Subjects Eight male and 16 female subjects participated in all experimental trials (mean age, height, and mass were 36.3718.5 yr, 1.6870.09 m, and 74.5713.9 kg, respectively). Experimental procedures received approval from the University of Windsor Research Ethics Board and subjects provided written consent prior to participation. Subjects were randomly recruited from the Windsor area through an employment agency and compensated accordingly for their time. Experimental trials took place at the University of Windsor—Human Kinetics Building. 2.2.2. Experimental procedures Experimental trials were conducted over a 12-day period. Subjects were divided into 2 equal groups. Each subject participated on 3 separate days (labelled 1, 2, and 3) in a constant section (morning or afternoon) with two other subjects (Table 2). Each day was divided into 4


144 Table 2 Subject seat position protocol Group 1—Day 1 Calendar 1

Session

Seat

Calendar 2

Position

C Null

A Down-in

B Down-out

A Up-in

B Up-out

Position

Morning section 9:00–9:20 1 9:30–9:50 2 10:00–10:20 3 10:30–10:50 4 11:00–11:20 5 11:30–11:50 6

1 2 3 2 1 3

2 3 1 N/A N/A N/A

3 1 2 N/A N/A N/A

N/A N/A N/A 3 2 1

N/A N/A N/A 1 3 2

9:00–9:20 9:30–9:50 10:00–10:20 10:30–10:50 11:00–11:20 11:30–11:50

Afternoon section 1:00–1:20 7 1:30–1:50 8 2:00–2:20 9 2:30–2:50 10 3:00–3:20 11 3:30–3:50 12

4 5 6 5 4 6

N/A N/A N/A 6 5 4

N/A N/A N/A 4 6 5

5 6 4 N/A N/A N/A

6 4 5 N/A N/A N/A

1:00–1:20 1:30–1:50 2:00–2:20 2:30–2:50 3:00–3:20 3:30–3:50

Session

Seat C Null

A Down-in

B Down-out

A Up-in

B Up-out

13 14 15 16 17 18

7 8 9 8 7 9

8 9 7 N/A N/A N/A

9 7 8 N/A N/A N/A

N/A N/A N/A 9 8 7

N/A N/A N/A 7 9 8

19 20 21 22 23 24

10 11 12 11 10 12

N/A N/A N/A 12 11 10

N/A N/A N/A 10 12 11

11 12 10 N/A N/A N/A

12 10 11 N/A N/A N/A

The above is an example of subject and seat positioning protocol. There were 6 days (12 calendar) of total testing. Each 30-min session was divided into a 20-min condition time, where subjects occupied an assigned seat and watched a movie, a 3–7-min evaluation period, where both the ASDQ and Automotive Seating Comfort Survey (Kolich, 2000) were administered, and a 3–7-min stretch period, where subjects walked around to prevent muscular ache and stiffness.

sections with 6 sessions. Each session was 30-min in duration. Three identical front driver-side seats (A–C) from a 2003 model sedan, were used throughout the project. Seats A and B were equipped with identical Schukra brand 4-way plastic power lumbar support systems (motion capabilities up/down and in/out) while seat C was not equipped with a lumbar support system. The seats were individually mounted on identical custom base supports to mimic seat fastening in an automobile. All 3 seats were subjected to an evaluation to verify that the seats being used and the lumbar supports fitted in seats A and B were in fact identical. The report concluded that all 3 seats and the 2 lumbar supports had identical physical characteristics. The seats were situated in a row, 36 cm apart, to simulate a typical automotive seating design. Dividers were erected and hung between the seats during questionnaire response to restrict visual contact between subjects. A movie was played during each session, doubling as subject entertainment and as a distraction. Five seat positions were used (Table 2): Down-In (1), Down-Out (2), null (3,6), Up-In (4), and Up-Out (5). These labels corresponded with specific lumbar support positioning. ‘‘Up’’ refers to the lumbar support being located at the vertical maximum of its tracking. ‘‘Down’’ refers to the lumbar support being situated at the vertical base of its tracking. ‘‘In’’ refers to the lumbar support plastic in a non-engaged (no curvature present) position. ‘‘Out’’ refers to the lumbar support plastic in a maximally engaged (maximum curvature) position. Seat A was always in the ‘‘In’’ position and seat B was always in the ‘‘Out’’ position.

Seat A was used for seat positions 1 and 4, seat B for seat positions 2 and 5, and seat C for seat positions 3 and 6. All subjects experienced the null seat position twice a day where as the other positions were only experienced once. Seat C positions 3 and 6 (seat position 6 is the position label for the second instance each subject was assigned to the null seat position on a given day) were used to confirm uni-variate reliability between subject responses. Subjects were randomly assigned identifying numbers that corresponded with predetermined randomized seating positions for each session. Subjects were required to sit in the assigned seat continuously for 20 min and were instructed to position themselves in an everyday driving posture that included placing their right leg in an outstretched position to simulate interaction with the accelerator pedal. Every 4 min, subjects were asked to take their right arm and reach outwards to simulate realistic motions used to interact with an automobile instrument panel (i.e. radio, heat controls). The ASDQ and the Automobile Seat Comfort Survey (Kolich, 2000) were administered after each 20-min seating session. This timeframe allowed the seat foam to approach its base-line properties (Reed and Massie, 1996). [Note: the version of the Automobile Seat Comfort Survey used was an intermediate version that contained 3 extra variables all shown to have statistically significant reliability in Kolich (2000).] Questionnaire completion took subjects between 3 and 7 min. Subjects were instructed to vacate the experiment room for 3–7 min post-evaluation. During this time, each seat containing a lumbar support was manipulated to


2.2.3. Statistical analysis Visual analog scale scores from the ASDQ were measured and recorded. Answers from the Automobile Seat Comfort Survey (Kolich, 2000) were also recorded using the established Likert scale values from 3 to 3. Factor analysis and sub-scale calculations were established using the same methods as pilot test #3. ASDQ identified sub-scales and sub-scale repeatability (Cronbach’s a value) were compared to pilot #3 data as well as the double null seat position (seat C). A 2 (gender) 3 (day) 5 (seat position) mixed repeated measures analysis of variance (ANOVA) was performed on ASDQ discomfort scores. Tukey HSD post hoc analyses were performed to identify any significant differences (Statistica v. 5.0, StatsSoft, Tulsa, OK). Alpha was set at 0.05 for all comparisons. The scales used by the ASDQ and the Automotive Seating Comfort Survey (Kolich, 2000) were not equivalent. In order to directly compare scores between questionnaires, ASDQ VAS scores had to be converted into an absolute using the Likert scale values between 3 and 3, similar to that described in Kolich (2000). Variables common to both questionnaires were identified. A paired two-sample t-test for each response score was used to note significant differences between questionnaire scores.

support for included source items. Cronbach’s a was above 0.8 for the 3 factors labeled as Trim, Cushion, and Lumbar sub-scales. 3.2. Establishing the ASDQ—experimental Factor analysis identified 4 significant levels in experimental data. An analysis of significant components identified these variable sub-scales as Lumbar, Trim, Backrest, and Cushion. Varimax rotated component values were used to assign each variable and its associated question to a sub-scale (Fig. 1). Notably, variable labels cushion bolster (q.7) and backrest contour (q.14) were grouped within two sub-scales. Each variable expressed a high rotation value for both stated factors as well as having a high correlation with all variables contained within that sub-scale. A significant difference between ASDQ discomfort ratings for seat positions 4 and 5 was found (p ¼ 0:043) (Fig. 2). All other main effects and interactions were not statistically significant. This supports that the ASDQ measures the construct of discomfort without bias and is responsive to subjective differences in perceived discomfort associated with physical components of the seat. Total Number of Variables

coincide with the predetermined seat positioning for each session as well as permitting subjects the opportunity to walk around and/or stretch before the next session. Subjects re-entered and repeated these procedures until all sessions were completed for that day. Once all 3 days were completed, subjects were verbally debriefed about the purpose of the study and thanked for their participation.

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7 6 5 4 3 2 1 0

α = 0.921*

α = 0.959*

α = 0.917*

α = 0.975*

1,2,3 Trim

4,5,6,7,8,9 Cushion

7,10,11,12,13,14 14,15,16,17,18,19 Backrest Lumbar

Questions Contained in each Sub-scale

3. Results

* Cronbach's α > 0.070 is significant.

3.1.1. Key informant interviews Key informant interview sessions resulted in a decrease of source items from 30 to 26 as well as numerous wording changes (Table 1). The resultant Flesch–Kincaid readability score was 7.2, thus a proper level of readability was obtained. Face validity requirements, as per Streiner and Norman (2003), were achieved. 3.1.2. Pilot testing A lack of correlational significance between key source items (po0:2) resulted in the deletion of 6 and the rewording of 3 items from the ASDQ. Both modifications resulted in increased questionnaire readability and statistical significance. Twenty source items found to contribute to the construct of seating discomfort were ultimately identified (Table 1). The final ASDQ Flesch–Kincaid value was 7.0. A factor analysis exposed 3 distinct factors, providing further

Fig. 1. ASDQ sub-scale variable by question breakdown. Cronbach’s a values for the 4 identified sub-scales were found to be significant. The total number of variables and the associated variable question identifiers contained within each sub-scale are presented.

Mean ASDQ Discomfort Score (/10)

3.1. Development of the ASDQ

5 4 p = 0.043 3 2 1 0 1

2

3 Seat Position

4

5

* Significant difference (p< 0.05) Fig. 2. Plot of meansseat position. A significant difference was found for subject response scores on the ASDQ between seat positions #4 and #5 using a mixed repeated measure ANOVA. All other seat position interactions were not found to be significant.


Of the 13 questions addressed in the Automotive Seating Comfort Survey, 10 were comprised of similar variables/ sub-scales found in the ASDQ (Table 3). A high between questionnaires subject response correlation was found (R2 ¼ 0:715). Between questionnaire values for sub-scale reliability addressing labels ‘Cushion’, ‘Backrest’, and ‘Entire seat’ were significant due to correlation coefficients of 0.64, 0.60, and 0.69, respectfully. When compared to converted ASDQ-relative scores (Fig. 3), Automotive Seating Comfort Survey scores were higher for 8 of the 10 interactions and possessed an average mean difference of 3.5% between questionnaire variable response scores. 4. Discussion The ASDQ (Appendix A) was developed with acceptable levels of readability, significant questions and wording, face validity, high levels of VAS repeatability, and reliable and internally consistent sub-scales. The ASDQ was not influenced by gender, but was sensitive to changes within the physical components of the seat. Subject perceptions on the ASDQ were shown to be consistent over time. The aim to include key variables contributing to the construct of automotive seating discomfort was supported. Face validity was established in the interview and review process in accordance with Streiner and Norman (2003). Pilot tests #1 and #2 resulted in the inclusion of only statistically significant questions and wording in the ASDQ. Readability levels were significant throughout development due to optimal Flesch–Kincaid scores.

Table 3 Between questionnaire equivalent variable listing Automotive Seating Comfort Survey

ASDQ

A—lumbar support B—lumbar comfort E—back lateral support F—back lateral comfort G—seat back feel/firmness H—ischial/buttock comfort J—cushion length K—thigh comfort L—cushion lateral comfort M—cushion feel/firmness

17—lumbar support LMBR—lumbar sub-scale 11—backrest width 13—backrest bolsters 12—backrest firmness 8—cushion center 5—cushion length 4—cushion width 7—cushion bolsters 6—cushion firmness

A total of 10 similar variables contained within the Automotive Seating Comfort Survey (Kolich, 2000) and the ASDQ are listed with their between questionnaire equivalent.

2.5 2.0 1.5

*

*

*

*

Automotive Seating Comfort SurveyKolich (2000)

*

*

ASDQ - Relative Score

1.0 ASDQ - VAS Score

0.5 0.0 J5 K4 L7 M -6

3.3. Between-questionnaire comparisons

3.0

A B- -17 LM BR E11 F13 G -1 2 H -8

A Pearson correlation of 0.71 was found to be significant (p ¼ 0:05) for null seat positions 3 and 6. Thus, subject responses to the null seat position were similar throughout all trials. This supports that individual subjective perceptions of discomfort remain consistent over time and that the VAS contains a significant level of reliability.

Response Score

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Equivalent Questions * Significant difference (p < 0.05) between the Automotive Seating Comfort Survey and the ASDQ-Relative score using a t-Test: Paired Two Sample for Means. Fig. 3. Between questionnaire response comparison. ASDQ relative scoring is defined as ASDQ VAS scores converted into an absolute Likert scale score between 0 and 3 (as seen in Kolich, 2000) by dividing each score by 3.333. The resultant values were binned using a conversion protocol between 0 and 3 (i.e. 00.74 ¼ 0, 0.751.49 ¼ 1).

Ultimately, subjects responded that the ASDQ was easy to use and expressed little concern during response times, offering further support for the structure and layout of the ASDQ. To ensure trial realism, experimental set-up was controlled for internal and external factors affecting the occupant. Mandatory physical movements forced subjects to stay mobile during each session in accordance with Jung and Choe (1996). This considerably increased the realism of the study. The 20 min seat duration provided a realistic trial duration and supports the conclusion of Reed and Massie (1996) that 20 min is an acceptable duration for static automotive seating simulation. The absence of seat vibration from the experimental set-up allowed for the direct identification of contributing physical seat components to occupant seating discomfort. Thus, the experimental set-up was considered appropriate for performing automotive seating simulations. A significant difference was found between seat position 4 and 5. The differences between these positions offer an explanation for the identified main effect. Seat position 4 had minimal support where as seat position 5 maintained maximum support to the mid-region of the backrest. For most individuals this would result in the lumbar support system being placed in the thoracic region of the back, creating an opportunity to sense discomfort. No significant gender, day, gender vs. day, gender vs. seat position, and/or day vs. seat position effects were seen, providing evidence that a VAS was an appropriate choice to quantify the construct of discomfort. This was expected due to the high levels of scale reliability and response repeatability between gender, days, and seat position contained within the ASDQ. Between-subject variability (standard deviation) suggests that subjects have different perceptions of discomfort but are able to maintain this perception over time. Also, mean subject response averages


were consistent throughout all analyses supporting the definition of discomfort to include ‘mild form of pain’ and as an appropriate measure for evaluating automotive seating discomfort. A large body of literature in which VAS scales were shown to be reliable and consistent supports these findings (Giacomin and Quattrocolo, 1997; Streiner and Norman, 2003; Tijhuis et al., 2003; van der Eijk et al., 2001). Comparisons between the Automotive Seating Comfort Survey and the ASDQ were positive. A relative score comparison between similar questionnaire variables resulted in an R2 ¼ 0:715. Two omitted Automotive Seating Comfort Survey variables (J, M) were shown to be significant and used in all between questionnaire comparisons. These findings support the use of a preliminary version of the Kolich (2000) Automotive Seating Comfort Survey. A factor analysis of experimental trial data identified ‘Lumbar’, ‘Trim’, ‘Backrest’, and ‘Cushion’ as significant ASDQ sub-scales. Sub-scale reliability (Pearson r40:8) was significant, confirming each sub-scale variable was homogeneous and allocated properly. However, a discrepancy between ASDQ pilot test #3 and experimental trial data was identified. Pilot test #3 identified 3 principal components whereas experimental trial data identified 4. Sub-scales ‘Trim’ and ‘Cushion’ had similar results, however, sub-scale ‘Lumbar’ differed dramatically between the 2 data sets. Pilot test #3 data resulted in backrest related seat components to be grouped into the ‘Lumbar’ sub-scale. Low sample size and an experienced population in pilot test #3 directly affected exposing only 3 out of 4 eventual sub-scales. Comparing data sets from the Automotive Seating Comfort Survey and pilot test #3 resulted in high correlation values and strong internal consistencies. Both data sets were also unable to show ‘Backrest’ and ‘Lumbar’ sub-scales as distinct. However, when sample size was increased in the ASDQ and an inexperienced subject population was solicited, ‘Lumbar’ and ‘Backrest’ subscales were shown to be significantly separate and distinct. This supports that sample size and seat selection had an impact on resultant questionnaire content. The lack of division between ‘Lumbar’ and ‘Backrest’ components and the lack of a ‘Trim’ sub-scale greatly diminishes the detail presented in questionnaire results. A between questionnaire comparison resulted in similar mean responses and minimal percent mean differences between ASDQ and Automotive Seating Comfort Survey subject response data. A significant correlation was found between comparable questionnaire sub-scales. These findings suggest that both questionnaires are measuring the same construct. However, differences between 6 of the 10 compared source item variables were found to be significant (po0:05). These differences are likely due to sub-scale structure variation between questionnaires. ASDQ VAS usage allowed subjects higher levels of freedom when establishing their perceived level of

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discomfort. The Automotive Seating Comfort Survey forced subjects to select an anchored point, removing subjective control and the freedom to provide an exact representation of their perceived discomfort. Since subjective perception was pre-defined in the Automotive Seating Comfort Survey, when a subject felt a level of discomfort between anchors, a forced decision was prompted due to an intermediate value being unavailable. Supporting this claim, questionnaire response scores were higher on the Automotive Seating Comfort Survey on 8 of 10 between questionnaire variable comparisons. The ASDQ allowed subjects to respond according to their own discomfort perception definition on a continuous scale, where as the Automotive Seating Comfort Survey pre-defines this perception through anchoring and forces the subject to respond in 1 of 7 defined ways. It is being suggested that the physical spacing between anchors in the Automotive Seating Comfort Survey produces a region of non-response that decreases the level of precision with which a subject is able to evaluate their perceived discomfort. This was seen to result in a lower level of detail present, the difference in overall number of variables used (ASDQ ¼ 20, Automotive Seating Comfort Survery ¼ 10), and overall questionnaire applicability and quality of results.

5. Conclusion The ASDQ contains significant questions and wording, readability, face validity, VAS repeatability, and reliable and internally consistent sub-scales. The ASDQ is sensitive to subjective perceptions of seating discomfort over time. The use of proper developmental methods resulted in a statistically significant, repeatable, reliable, and partially validated assessment tool for automotive seating discomfort. A between-questionnaire comparison exposed differences between a previously established questionnaire and the newly developed ASDQ. These differences support methodologies used and how the ASDQ is able to provide more detailed and comprehensive results than other questionnaires in the automotive seating industry. Therefore, it is concluded that the ASDQ is able to measure the construct of automotive seating discomfort in a reliable and detailed way as well as provide information on how areas of the seat contribute to overall occupant discomfort.

Acknowledgements The authors would like to thank Schukra of North America for their cooperation and funding throughout this project, Dr. Krista Chandler for statistical assistance.

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Appendix A. Automotive Seating Discomfort Questionnaire (ASDQ) (not actual size)

For full questionnaire please contact the authors.

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