IN (FRAIL) OLDER PEOPLE, maintaining or improving

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1 1892 ORIGINAL ARTICLE Reproducibility and Validity of the Dutch Translation of the de Morton Mobility Index (DEMMI) Used by Physiotherapists in Older Patients With Knee or Hip Osteoarthritis Marielle P. Jans, PhD, Vera C. Slootweg, MSc, Cecile R. Boot, PhD, Natalie A. de Morton, PhD, Geert van der Sluis, BA, Nico L. van Meeteren, PhD ABSTRACT. Jans MP, Slootweg VC, Boot CR, de Morton NA, van der Sluis G, van Meeteren NL. Reproducibility and validity of the Dutch translation of the de Morton Mobility Index (DEMMI) used by physiotherapists in older patients with knee or hip osteoarthritis. Arch Phys Med Rehabil 2011;92: Objective: To examine the reproducibility, construct validity, and unidimensionality of the Dutch translation of the de Morton Mobility Index (DEMMI), a performance-based measure of mobility for older patients. Design: Cross-sectional study. Setting: Rehabilitation center (reproducibility study) and hospital (validity study). Participants: Patients (N 28; age 65y) after orthopedic surgery (reproducibility study) and patients (N 219; age 65y) waiting for total hip or total knee arthroplasty (validity study). Intervention: Not applicable. Main Outcome Measures: Not applicable. Results: The intraclass correlation coefficient for interrater reliability was high (.85; 95% confidence interval, 71.93), and minimal detectable change with 90% confidence was 7 on the 100-point DEMMI scale. Rasch analysis identified that the Dutch translation of the DEMMI is a unidimensional measure of mobility in this population. DEMMI scores showed high correlations with scores on other performance-based measures of mobility (Timed Up and Go test, Spearman r.73; Chair Rise Time, r.69; walking test, r.74). A lower correlation of.44 was identified with the self-report measure Western Ontario and McMaster Universities Osteoarthritis Index. Conclusions: The Dutch translation of the DEMMI is a reproducible and valid performance-based measure for assessing mobility in older patients with knee or hip osteoarthritis. Key Words: Activities of daily living; Aged; Geriatric assessment; Mobility limitation; Rehabilitation; Reproducibility of results. From TNO Healthy Living, Leiden (Jans, van Meeteren); ActiVite, Leiderdorp (Slootweg); Department of Public and Occupational Health, EMGO Institute for Health and Care Research, VU University Medical Center, Amsterdam (Boot), and Nij Smellinghe Hospital, Drachten (van der Sluis), The Netherlands; and Musculoskeletal Research Centre and School of Physiotherapy, La Trobe University, Victoria (de Morton), Australia. Presented to the Royal Dutch Society of Physiotherapy, November 13, 2009, Amsterdam, The Netherlands. Supported by a National Health and Medical Research Council of Australia (NHMRC) Post Doctoral Fellowship (ID ). No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit on the authors or on any organization with which the authors are associated. Reprints requests to Marielle P. Jans, PhD, University of Applied Sciences, School of Physiotherapy, Bolognalaan 101, 3584 CJ Utrecht, The Netherlands, marielle.jans@hu.nl /11/ $36.00/0 doi: /j.apmr by the American Congress of Rehabilitation Medicine IN (FRAIL) OLDER PEOPLE, maintaining or improving mobility is a common goal of therapy for physiotherapists. Monitoring mobility in older people demands reproducible and valid instruments. To assess mobility, 2 main approaches exist: self-report and performance-based measures. 1-3 Self-report measures rely on a person s perception and may be performed by using questionnaires. In contrast, performance-based measures rely on a rater s assessment of a person s performance of specific physical tasks. These measures may provide complementary information. 1-3 In older patients with knee or hip osteoarthritis, the selfreported questionnaire Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) often is used to measure physical functioning. 4,5 Performance-based measures frequently used in this population are the Timed Up and Go (TUG), 6 Chair Rise Time (CRT), 7 and walking tests. Disadvantages of these tests are that they provide information about only 1 component of mobility and nonambulant patients are unable to perform these tests, resulting in floor effects. 8 The de Morton Mobility Index (DEMMI) is a performancebased test recently developed to assess the mobility of older hospitalized patients. 9 The DEMMI measures transfers, static and dynamic balance, and walking and is a reproducible and valid test for accurately measuring mobility levels of older acute hospitalized patients. 9 Clinimetric properties of the English DEMMI have been investigated extensively in the hospital 9,10 and community settings. 11 Now the DEMMI has been translated into Dutch. The aim of this study was to examine the interrater reproducibility, validity, and unidimensionality of the Dutch translation of the DEMMI used by physiotherapists in daily clinical practice in a population of older patients with knee or hip osteoarthritis. 6MWT CI CRT DEMMI ICC MDC 90 TUG WOMAC List of Abbreviations six-minute walk test confidence interval Chair Rise Time de Morton Mobility Index intraclass correlation coefficient minimal detectable change with 90% confidence Timed Up & Go Western Ontario and McMaster Universities Osteoarthritis Index

2 DUTCH TRANSLATION OF THE de MORTON MOBILITY INDEX, Jans 1893 METHODS Translation We used the forward-backward translation method recommended by Guillemin et al. 12 Two qualified translators independently translated the DEMMI into Dutch. Two other translators independently back-translated each translation into English. All translators were highly educated, translated the DEMMI into their mother tongue, and had no specific knowledge of osteoarthritis. Because physiotherapists are the users of the DEMMI, the Dutch translation subsequently was submitted to 3 physiotherapists working in a clinical setting to ensure that the translation was fully comprehensible for Dutch physiotherapists. Unclear instructions were clarified after discussion with the test developer (N.A.d.M.). The mentioned physiotherapists pilot tested the translation in a few patients. Measures of Mobility The DEMMI consists of 15 items, which include perform a bridge, roll onto side, lie to sit, sit unsupported in chair, sit to stand from chair, sit to stand without using arms, stand unsupported, stand feet together, stand on toes, tandem stand, walking distance, walking assistance, pick up pen from floor, walk backwards, and jump. The patient is asked to perform these items, and performance of each item is scored on 2- or 3-point response options, resulting in a maximum ordinal score of 19 points. By using a simple conversion scale located on the face of the original DEMMI, the ordinal score can be converted to an interval DEMMI score from 0 to 100, for which higher scores indicate greater independent mobility. 9 The DEMMI instrument includes a protocol with instructions per item. For the validity analysis, 4 other measures of mobility were used. The TUG is a functional test that requires a person to stand up, walk 3m, turn back, and sit down while being timed. 6 Studies showed good reliability and validity. 6,13 The CRT required patients to fold their arms across their chest and stand up from a chair. If successful, the test was repeated 10 times as quickly as possible while being timed. 7 It is a reliable and valid test to measure lower-body strength. 13 The 6-Minute Walk Test (6MWT) assesses the distance a person can walk on a measured walkway during 6 minutes. It is a reliable and valid method to determine aerobic capacity and gait velocity in older people The WOMAC is a self-reported questionnaire for patients with knee or hip osteoarthritis consisting of 3 dimensions: pain (5 items), stiffness (2 items), and physical functioning (17 items). Responses are based on a 5-point Likert scale, from worst to best. The raw sum scores were standardized (0 100). 4,5 The Dutch translation showed satisfactory reliability and validity in patients waiting for total hip arthroplasty. 5 Reproducibility Sample We examined the reproducibility of the DEMMI between 2 physiotherapists, independently assessing 28 consecutively eligible patients 65 years or older admitted to a rehabilitation center in The Netherlands approximately 5 days after orthopedic surgery. Patients with severe dysphasia, documented contraindications to mobilizations, or isolation for infection or for whom death was imminent were excluded from this study. One physiotherapist worked at the hospital in which the surgery had been performed and the other worked at the rehabilitation center where this study was conducted. Both physiotherapists were men who had more than 5 years of experience in clinical physiotherapy, but were using the DEMMI for the first time. Before the start of the study, the physiotherapists discussed performance of the DEMMI, but no formal training was given. After the first assessment and a 10-minute rest, the DEMMI was repeated by the other physiotherapist, blinded to the outcomes of the first test. Each physiotherapist was the first assessor in half the patients. The test order of assessing physiotherapist was arbitrary. Data were obtained as part of usual care. Validity and Unidimensionality Sample We investigated the construct validity and unidimensionality of the DEMMI in 219 patients 65 years or older waiting for total hip or total knee arthroplasty. Exclusion criteria were the same as for the reproducibility study. Five to 6 weeks before surgery, a physiotherapist screened each patient for mobility as part of usual clinical care. Five physiotherapists from the same hospital in The Netherlands performed the screening protocol, including the DEMMI, after 1 short training session. We discussed the feasibility of the DEMMI in an interview with participating physiotherapists. Statistical Analysis De-identified data were used in the analyses. Data were analyzed using SPSS 17.0 a for Windows for all analyses except the Rasch analysis, which was completed using RUMM2020. b To describe the characteristics of the patient population, we used descriptive statistics. Normal distribution of mobility measure scores was determined by using quantile-quantile plots and the Shapiro-Wilk test of normality. Reproducibility. Reproducibility can be distinguished into 2 concepts: reliability and agreement. 17 Interrater reliability of DEMMI scores was evaluated by using intraclass correlation coefficient (ICC) model Agreement between raters was investigated by using the method of Bland and Altman 19 and minimal detectable change with 90% confidence (MDC 90 ). 20 The Bland-Altman method 20 is based on analysis of differences between paired measurements of 2 physiotherapists. Mean difference is a measure of systematic bias between the 2 raters that should be close to zero. First, differences between paired measurements were plotted against their mean. Second, the 95% limits of agreement (ie, mean difference 1.96SD of the difference) were constructed. To investigate systematic differences, paired t tests were performed between raters. Because a practice effect in patients might result in higher scores in the second round of measurements (both raters conducted half the measurements in the second round), systematic differences between the first and second measurements also were investigated by using paired t tests. MDC 90 is defined as the minimal amount of change that needs to occur between repeated assessments in an individual to exceed the error of the measurement itself. 20 MDC 90 was calculated as SE of measurement. Validity. DEMMI scores were inspected for possible floor and ceiling effects by determining the percentage of patients with the lowest and highest possible scores. A floor or ceiling effect was considered if the percentage of persons scoring the lowest or highest scale score was 15% or greater, respectively. 17 We assessed 2 aspects of construct validity: convergent validity and known-groups validity. To examine convergent validity, Spearman correlation coefficients were calculated between DEMMI scores and other measures of mobility. We hypothesized that the DEMMI would have higher correlation with patients scores on other performance-based measures of mobility (TUG test, 6 CRT, 7 6MWT 14 ) than with patients scores on a self-report measure of mobility (WOMAC 4 ). To compare correlations, z tests were used. To examine known-groups validity, DEMMI scores of patients with an expected discharge to home after surgery were compared with those expected to be discharged to inpatient rehabilitation,

3 1894 DUTCH TRANSLATION OF THE de MORTON MOBILITY INDEX, Jans expecting a significantly higher DEMMI score in patients with an expected discharge to home. Known-groups validity was investigated by using the nonparametric Mann-Whitney U test. Unidimensionality. Rasch analysis was used to investigate the unidimensionality of the DEMMI (ie, whether the Dutch translation is measuring the 1 construct of mobility as per the English DEMMI). The Rasch model is a probabilistic model that asserts that item response is a logistic function of item difficulty and person ability. The Rasch model also was used to identify a hierarchy of difficulty in items ranked from easiest to hardest. In this study, overall fit to the model was reported if item trait interaction chi-square P was greater than.05 and then confirmed by using the t test procedure recommended by Tennant and Pallant. 21 Item fit residuals greater than 2.5 were used to identify multidimensionality or redundancy. For most purposes, a sample size of 100 would provide 95% confidence within 0.5 logits. 22 The Rasch analysis was conducted on the entire sample of 219 persons. RESULTS Translation The 2 forward-backward translations yielded no differences in the description of DEMMI items (see Appendix 1). Some instructions in the protocol for administration of the DEMMI have been described in more detail after consulting the test developer (N.A.d.M.). Reproducibility The 2 physiotherapists assessed 28 patients (26 women; mean SD age, 73 8y). Fourteen patients underwent total hip replacement, 7 underwent total knee replacement, and 7 underwent other orthopedic surgeries. Nine patients used a walking aid. The DEMMI had no missing data. DEMMI scores were normally distributed (W.946; P.161) and ranged from 33 to 67. The ICC model 2.1 for DEMMI scores between raters was.85 (95% confidence interval [CI],.71.93). Mean DEMMI scores for the 2 raters were and , with a mean difference of.64 (95% CI, 1.0 to 2.2). Figure 1 shows the difference in DEMMI scores between the 2 raters plotted against mean scores. The 95% limits of agreement between raters were 7.4 to 8.7. Mean scores for the first and second Difference between raters Mean score of raters mean Fig 1. Bland-Altman plot: differences in DEMMI scores between 2 raters plotted against mean scores. The straight line represents the mean difference between both assessments; dotted lines represent the 95% limits of agreement. Table 1: Absolute Percentage of Agreement Between the 2 Raters per DEMMI Item Item Agreement (%) Perform a bridge 93 Roll onto side 100 Lie to sit 86 Sit unsupported in chair 100 Sit to stand from chair 86 Sit to stand without using arms 96 Stand unsupported 96 Stand feet together 96 Stand on toes 86 Tandem stand 96 Walking distance 93 Walking assistance 82 Pick up pen from floor 89 Walk backwards 82 Jump 100 round of measurements were and , respectively. The mean difference was 1.4 (95% CI, 2.9 to 0.1). Using a pooled SD of 7.6, the SE of measurement was 2.9 and the MDC 90 was 6.7 points (95% CI, ) on the 100-point DEMMI scale. The absolute percentage of agreement between the 2 raters per item varied from 82% to 100% (table 1). Validity Characteristics of the 219 patients are listed in table 2. Mean SD DEMMI score was No patient obtained the lowest score (0 points) and 12% obtained the highest possible score (100 points). Scores of all performance-based measures were not normally distributed (DEMMI: W.954, P.001; TUG Table 2: Patient Characteristics for the Validation Study Characteristic No. of Subjects Value Women (%) Mean age (y) Planned operation 216 Total hip arthroplasty (%) 68 Total knee arthroplasty (%) 32 Arthroplasty at contralateral 29 side (%) 219 Place of residence 219 Home with stairs (%) 58 Apartment (%) 39 Nursing home/home for the elderly (%) 3 Expected discharge 207 Home (%) 66 Inpatient rehabilitation (%) 25 Unknown/other (%) 9 Mean DEMMI total score (range, ) Mean TUG test time (s) (range, 4 47) Mean CRT time (s) (range, 6 171) Mean 6MWT distance (m) (range, ) Mean WOMAC total score (range, 5 91) Mean WOMAC physical functioning score (range, 3 90) NOTE. N 219.

4 DUTCH TRANSLATION OF THE de MORTON MOBILITY INDEX, Jans 1895 Table 3: Spearman Correlation Coefficients ( ) of DEMMI Scores With Scores of Other Performance-Based and Self-report Measures of Mobility in a Population of Patients Waiting for Total Hip or Total Knee Arthroplasty Domain Measure No. of Subjects Performance based Self-report Correlation Coefficient ( ) TUG test CRT MWT WOMAC total score WOMAC physical functioning WOMAC pain WOMAC stiffness test: W.869, P.001; CRT: W.847, P.001; 6MWT: W.984, P.02). As listed in table 3, DEMMI scores had higher correlation with scores for the other performancebased measures of mobility (TUG test, CRT, 6MWT) than with the self-report measure WOMAC. The z tests showed that these differences in correlation coefficients were significant (P.05). A significant difference (Mann-Whitney U 1899; P.001) in DEMMI score was observed between patients with expected discharge to home after surgery (mean SD, 76 17) and those with expected discharge to a rehabilitation center (mean SD, 62 16). Unidimensionality Results of Rasch analysis indicated that the hierarchy of item difficulty of the Dutch translation of the DEMMI was similar to that of the original English version during DEMMI development in an older acute hospitalized population 9 (fig 2). The only item that did not have overlapping 95% confidence bands for item logit location was the item walking assistance. Tandem stand with eyes closed was the most difficult item and sit unsupported was the easiest item in both the Dutch and Australian data sets. In the Dutch sample (N 219), some overall deviation from the Rasch model was identified, with an item trait interaction P.004 ( ; P.004). However, the t test procedure recommended by Tennant and Pallant indicated unidimensionality with a point estimate of 1.04%. The items walking backwards (P.00; fit residual, 2.62) and sit to stand without using arms (P.00; fit residual, 3.14) showed mild deviation from that expected by the Rasch model. Feasibility According to the physiotherapists participating in this study, the DEMMI was safe and easy to administer (10 15min) and had minimal equipment requirements (chair and stopwatch). Instructions on the DEMMI were clear enough for physiotherapists to administer the DEMMI. DISCUSSION This was the first study of the reproducibility and validity of the Dutch translation of the DEMMI used by physiotherapists and performed in a population of older people with knee or hip osteoarthritis. Interrater reliability between 2 physiotherapists was good. There were no systematic differences between the 2 raters. The MDC 90 indicated that a patient needs to improve or deteriorate by 7 or more points for a physiotherapist to be 90% confident that a true change in patient condition has occurred. Interrater reliability between the 2 physiotherapists in this study was similar to the high reliability (Pearson r.94; 95% CI,.86.98) reported by the test developers in an older acute medical population and for which the physiotherapists had more experience with applying the DEMMI. 9 In addition, the MDC 90 was similar to that of 9.5 points (95% CI, ) found in the Australian study. 9 In this population, the DEMMI showed no floor and ceiling effects because no patient obtained the lowest score and less than 15% of patients obtained the highest score. The DEMMI showed higher correlations with scores for other performancebased measures of mobility in comparison to the correlation between the DEMMI and a self-report measure of mobility. These findings support the convergent validity of the DEMMI in older people with knee or hip osteoarthritis. The test developers found similar results with respect to validity in an older acute medical population. In their study, DEMMI score correlated higher with the performance-based measure Hierarchical Assessment of Balance and Mobility (r.91) than with the self-report measure Barthel Index (r.68) Logit location (95% CI) Dutch Australian -6 Fig 2. Item hierarchy of difficulty of the Dutch and Australian 9 DEMMI data, constructed by using Rasch analysis. -8 sit unsupported bridge stand unsupported sit to stand roll lie to sit distance walked stand feet pick up pen walk backwards sit to stand no arms walking assistance stand on toes jump tandem st eyes cl

5 1896 DUTCH TRANSLATION OF THE de MORTON MOBILITY INDEX, Jans Rasch analysis indicated that items in the Dutch translation of the DEMMI measure the same construct and the Dutch translation of the DEMMI is a unidimensional measure of mobility. The hierarchy of item difficulty was similar in the Dutch and Australian 9 populations despite being different clinical populations. The only difference was the item walking assistance, which was relatively easier to score in the Dutch study than the Australian study. This likely is a result of the different clinical populations between studies, in which walking independently for 50m was identified as a more difficult task in acute hospitalized patients than in patients with knee or hip osteoarthritis. The promising reproducibility, validity, and feasibility indicate that the Dutch translation of the DEMMI is useful to physiotherapists and researchers to measure mobility in older patients with knee or hip osteoarthritis. Study Limitations The obtained sample size of 28 in the reliability study, as well as the sample size in the original reliability study of the DEMMI (N 21), 9 generally were considered small for a reliability study with respect to the external validity of the findings. 17 However, a posterior power analysis showed that a sample size of 28 with 2 raters per subject achieved 80% power to detect an ICC of.85 under the alternative hypothesis when the ICC under the null hypothesis is.65 or lower. Furthermore, the lower limit of the 95% CI of the ICC was.71, which is higher than the recommended minimum standard of reliability. 17 Both studies of the DEMMI were conducted in a population of patients with a small range of diagnoses, and only 2 raters were involved in the reproducibility study. To get more insight into the clinimetric characteristics of the DEMMI in daily clinical practice, complementary studies are needed, performed in a clinical context in which the DEMMI will be used by a clinically relevant variety of raters. We also recommend reproducibility studies in patients with more diverse pathologic states and mobility problems and in other settings in which physiotherapists take care of older frail patients (ie, nursing home, rehabilitation center). Furthermore, more research is needed for test-retest reproducibility, responsiveness, and predictive value of the Dutch translation of the DEMMI. CONCLUSIONS This study provides evidence that the Dutch translation of the DEMMI is a unidimensional, reproducible, valid, and feasible measure of mobility for use by physiotherapists in older patients with knee or hip osteoarthritis. The simplicity and utility of the DEMMI make this instrument easy to fit into usual clinical care.

6 DUTCH TRANSLATION OF THE de MORTON MOBILITY INDEX, Jans 1897 APPENDIX 1: THE DUTCH TRANSLATION OF THE de MORTON MOBILITY INDEX (DEMMI)

7 1898 DUTCH TRANSLATION OF THE de MORTON MOBILITY INDEX, Jans

8 DUTCH TRANSLATION OF THE de MORTON MOBILITY INDEX, Jans 1899 References 1. Wittink H, Rogers W, Sukiennik A, Carr CB. Physical functioning: self-report and performance measures are related but distinct. Spine 2003;28: Reuben DB, Seeman TE, Keeler E, et al. Refining the categorization of physical functional status: the added value of combining self-reported and performance-based measures. J Gerontol A Biol Sci Med Sci 2004;59: Stratford PW, Kennedy DB, Riddle DL. New study design evaluated the validity of measures to assess change after hip or knee arthroplasty. J Clin Epidemiol 2009;62: Bellamy N, Buchanan WW, Goldsmith CH, Campbell J, Stitt LW. Validation study of WOMAC: a health status instrument for measuring clinically important patient relevant outcomes to antirheumatic drug therapy in patients with osteoarthritis of the hip or knee. J Rheumatol 1988;15: Roorda LD, Jones CA, Waltz M, et al. Satisfactory cross cultural equivalence of the Dutch WOMAC in patients with hip osteoarthritis waiting for arthroplasty. Ann Rheum Dis 2004;63: Podsiadlo D, Richardson S. The timed Up & Go : a test of basic functional mobility for frail elderly persons. J Am Geriatr Soc 1991;39: Cuska M, McCarthy DJ. Simple method for measurement of lower extremity muscle strength. Am J Med 1985;78: de Morton NA, Berlowitz DJ, Keating JL. A systematic review of mobility instruments and their measurement properties for older acute medical patients. Health Qual Life Outcomes 2008;6: de Morton NA, Davidson M, Keating JL. The de Morton Mobility Index (DEMMI): an essential health index for an ageing world. Health Qual Life Outcomes 2008;6: de Morton N, Lane K. Validity and reliability of the de Morton Mobility Index (DEMMI) in the subacute hospital setting in a geriatric evaluation and management population. J Rehabil Med 2010;42: Davenport S, de Morton NA. The clinimetric properties of the de Morton Mobility Index in healthy, community-dwelling older adults. Arch Phys Med Rehabil 2011;92: Guillemin F, Bombardier C, Beaton D. Cross-cultural adaptation of health-related quality of life measures: literature review and proposed guidelines. J Clin Epidemiol 1993;46: Hayes, KW, Johnson ME. Measures of adult general performance tests. Arthritis Rheum 2003;49(Suppl 5):S Harada ND, Chiu V, Stewart AL. Mobility-related function in older adults: assessment with a 6-minute walk test. Arch Phys Med Rehabil 1999;80: Bean JF, Kiely DK, Leveille SG, et al. The 6-Minute Walk Test in mobility-limited elders: what is being measured? J Gerontol A Biol Sci Med Sci 2002;57:M Kennedy DM, Stratford PW, Wessel J, Gollish JD, Penney D. Assessing stability and change of four performance measures: a longitudinal study evaluating outcome following total hip and knee arthroplasty. BMC Musculoskelet Disord 2005;6: Terwee CB, Bot SDM, de Boer MR, et al. Quality criteria were proposed for measurement properties of health status questionnaires. J Clin Epidemiol 2007;60: McGraw K, Wong S. Forming inferences about soms intraclass correlation coefficients. Psychol Methods 1996;1: Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1986;1: Stratford PW, Binkley JM, Riddle DL. Health status measures: strategies and analytic methods for assessing change scores. Phys Ther 1996;76: Tennant A, Pallant J. Unidimensionality matters! (A tale of two Smiths?) Rasch Measurement Trans 2006;20: Linacre J. Sample size and item calibration stability. Rasch Measurement Trans 1994;7:328. Suppliers a. SPSS, 233 S Wacker Dr, 11th Fl, Chicago, IL b. Perth RUMM Laboratory, 14 Dodonaea Ct, Duncraig, WA, Australia 6023.