Psychometric characteristics of PIMS—Compared to PDQ39 and PDQL—To evaluate quality of life in Parkinson's disease patients: Validation in Spanish (Ecuadorian style)

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  Analyze PIMS (Parkinson's impact scale) properties following the recommendations of the Scientific Advisory Committee of the Medical Outcomes Trust.An analytical cross-sectional study to evaluate the psychometric qualities and scale assumptions
  Parkinsonism and Related Disorders 14 (2008) 126–132 Psychometric characteristics of PIMS—Compared to PDQ-39 andPDQL—To evaluate quality of life in Parkinson’s disease patients:Validation in Spanish (Ecuadorian style) Marcos Serrano-Duen ˜as a,b,  , Soledad Serrano b a Neurological Service, Hospital Carlos Andrade Marı´ n, Ecuador b Medicine Faculty, Pontificia Universidad Cato´ lica del Ecuador. P.O. Box 17-03-A1694, Quito, Ecuador Received 29 March 2007; received in revised form 22 June 2007; accepted 10 July 2007 Abstract Objective:  Analyze PIMS (Parkinson’s impact scale) properties following the recommendations of the Scientific Advisory Committee of the Medical Outcomes Trust. Methods:  An analytical cross-sectional study to evaluate the psychometric qualities and scale assumptions of PIMS: quality of data,acceptability, reliability, validity, internal consistency, and construct validity. Results:  The sample included 131 patients with Parkinson’s disease (PD), of which 39 (29.7%) were women. Psychometric qualities andscale assumptions, all of them are suitable. Conclusions:  We therefore believe that PIMS is a useful and recommendable specific tool for measuring quality of life in PD patients. r 2007 Elsevier Ltd. All rights reserved. Keywords:  Metric properties; Quality of life; Parkinson’s disease; PIMS; PDQL; PDQ-39; Validity 1. Introduction Parkinson’s disease (PD) is a chronic, progressiveneurodegenerative disease that causes motor symptoms(rest tremor, bradykinesia, rigidity and loss of posturalreflexes), neuropsychiatric symptoms (depression, anxiety,dementia, apathy, psychosis), autonomic symptoms (urinaryincontinence, orthostatic hypotension and sexual dysfunc-tion, among others), and a set of signs and symptomsthat do not fit into the previous groups: dysphagia,drooling, seborrhea [1 – 3]. Its epidemiology shows an overall prevalence of 1 out of every 1000 inhabitants, anda specific prevalence of 1 out of every 100 inhabitants in the65+ age group [2,4,5]. The disease causes a progressive deterioration in diffe-rent aspects of a patient’s state of health and in his/herindependence and ability to function, producing a clearlynegative impact on health-related quality of life (HRQoL),which is broadly understood to mean the individualperception that a subject has as to the effect of the diseaseprocess and of its medical treatment on his/her life [6–8].Moreover, as recently pointed out [9], the very fact that it is a chronic illness entails the greater possibility of causing anegative impact on the quality of life.Specific scales have been designed to evaluate theHRQoL construct in patients with PD, among themParkinson’s impact scale (PIMS), which demonstratedsuitable values on first validation, both with respect tointernal consistency (0.89 Cronbach  a ) and to test–retestreliability (0.72) [10]. Another study on its psychometricproperties [11] that involved a sample of patients undermedical treatment also demonstrated suitable character-istics (0.87 Cronbach  a ; ICC 0.82). Construct validity andsensitivity to change as measured in stable patients throughUPDRS section II were equally suitable (  p o 0.0001).Later on [12], it was used to evaluate the quality of lifeof PD patient caretakers and again showed suitable ARTICLE IN PRESS$-see front matter r 2007 Elsevier Ltd. All rights reserved.doi:10.1016/j.parkreldis.2007.07.006  Corresponding author. Tel.: +59322542678. E-mail address: (M. Serrano-Duen˜as).  psychometric properties. Nevertheless, one review of scalesmeasuring PD quality of life fails to mention it [13], andanother questions its soundness [14].To the best of our knowledge, no study has beenconducted to analyze any PIMS properties following therecommendations of the Scientific Advisory Committeeof the Medical Outcomes Trust [15]; much less anycomparative study with PDQ-39 [16] and PDQL [17] (considered the most reliable tools [13,14]) in the same sample of PD subjects, so that their similarities anddifferences can be evaluated, thus enabling a more exact judgment when choosing which tool to apply for measuringHRQoL.With this main objective, we designed this analyticalcross-sectional (one point) study to evaluate the psycho-metric qualities and scale assumptions of PIMS: qualityof data, acceptability, reliability, validity, internal consis-tency, and construct validity. Other goals were to comparePIMS, PDQ-39, and PDQL regarding some of theseproperties; appraise PIMS in the population studied bydichotomizing it into fluctuators and non-fluctuators,depressed and non-depressed, and patients with andwithout nervous tension; and finally, validate PIMS inthe typical Spanish of Ecuador. 2. Patients, materials, and methods We performed the translation–retrotranslation process along with asearch for the appropriate PIMS semantic equivalence, strictly followingthe recommendations for this transcultural validation [18 – 21], including a pilot study conducted in 20 subjects before obtaining the version that wasused in the study.The sample included 131 patients with PD, according to UKPDSBBcriteria [22]. They were chosen consecutively from among all theoutpatients visiting the Clinic of Movement Disorders of the NeurologyService at Carlos Andrade Marı ´n Hospital (HCAM), Quito, Ecuador.Patients with any serious concomitant illness were excluded, as werepatients with problems of aphasia, those that had CVD sequelae,blindness, amputation of any limb, or showing cognitive impairment(a score of six or higher on the SPMSQ). This is a methodology that hasbeen used before [23,24].The first evaluation included relevant demographic data, the degreethat daily activities were affected according to S&E [25], the staging of theillness according to H&Y [26], mood as per HADS [27], and frame of mind with Pfeiffer’s SPMSQ [28]. The degree to which motor functions were compromised was also quantified with SPES/SCOPA [29]. Finally, PIMSwas self-applied.Seven days later (ranging from 5 to 9), a second evaluation was carriedout with UPDRS [30] sections I–III, and PDQ-39 was self-administered tothe first 65 patients; while PDQL and the above-mentioned UPDRSsections were self-applied to the 66 remaining patients. Fifteen days later,(ranging from 14 to 18) the third valuation was done and PIMS was againself-applied.All the evaluations were done in the best functional state, known asON. The time taken in applying PIMS and SCOPA/SPES, on firstevaluation, and PDQ-39 or PDQL and the UPDRS (sections I–III), onsecond evaluation, was recorded.Parkinson’s impact scale [10] contains 10 items (Self (Positive), Self (Negative), Family Relationships, Community Relationships, Work,Travel, Leisure, Safety, Financial Security, and Sexuality), and it allowsthe patient to identify him/herself as having either stable symptomatologyor fluctuating symptomatology. In the latter case, he or she must fill inthe answers on their situation both in the best state and in the worst.When carrying out all the statistical analyzes in these patients, we did soby obtaining the mean between their best and worse situations.This study had the approval of the Teaching and Research Adminis-trative Office of the HCAM, and all the patients gave their informedconsent in writing. 3. Statistical analysis [15,21,31] 3.1. Quality of data Lost data should be less than 5% according to thesuggestion of Smith et al. [32]. 3.2. Acceptability Provide evidence that the scale has adequate variabilityin a range that is appropriate to its use: information of central tendency and dispersion, skewness, floor and ceilingeffects [33,34]. 3.3. Reliability (i) Internal consistency (the precision of a scale, based onthe homogeneity of the scale items at one point in time)using Cronbach  a : commonly accepted minimal standardsfor reliability coefficients are 0.70 for group comparisonsand 0.90–0.95 for individual comparisons. (ii) Test–reteststability (obtained by judging the reproducibility orstability of an instrument over time using ICC with 95%CI) values of 0.7 or greater are considered adequate [15]. 3.4. Validity This is defined as the degree to which the instrumentmeasures what it purports to measure. (i) Convergentconstruct validity explores the logical relationships thatshould exist with other accepted measures for the sameconstruct: using the Spearman  rho , values greater than 0.59are considered adequate [35]. (ii) Discriminative validity for‘‘known groups’’ based on the severity of disease (H&Y)was analyzed using the Kruskal–Wallis test.Patients were dichotomized as fluctuators and non-fluctuators (according to the criteria of Marsden et al. [36]),depressed and non-depressed, and anxious and non-anxious (cut-off point of 11 or more in the HADS Anxietyand Depression sections—according to the suggestion of the authors [27]). Differences between groups of patientsbased on the presence of fluctuations, depression, andanxiety were tested by means of the Mann–Whitney test.For all comparisons, we obtained mean values with 95%CI [31]. Then a comparison was done of similar attributesin the three scales employed: PIMS, PDQ-39, and PDQL. 4. Results The final sample was made up of 39 (29.7%) women and92 males with the following mean values: 68.8 years old; ARTICLE IN PRESS M. Serrano-Duen˜as, S. Serrano / Parkinsonism and Related Disorders 14 (2008) 126–132  127  illness duration of 7.8 years; 5.9 years in L-dopa treatment,and a dose of 767.3mg/day; level of compromise was66.7% on the S&E scale; total SPES/SCOPA score was26.5, with 69.2 on the UPDRS. There were six patients atH&Y stage 1.5, 25 at 2, 19 at 2.5, 70 at 3, and 11 at stages 4and 5. Thirty-six patients (27.4%) were fluctuators. TotalPIMS values were 18.3 in non-fluctuators and 25.4 influctuators (Tables 1 and 2).For our analysis we considered: (i) the 131 patients wereevaluated with SPES/SCOPA and PIMS; (ii) those withUPDRS and PDQ-39, 65 cases; and (iii) the evaluated withUPDRS and PDQL in 66 patients. 4.1. Quality of data and acceptability (i)  Quality of data : only PIMS item 10 had less than100% of the answers; we recorded 3.8% lost data. PDQLitem 36, also inquiring as to sexuality, had a lost data valueof 3.9%. Finally, we recorded 0.7% loss for PIMS item 2,3.9% for PDQL item 22, and 3.9% for PDQ-39 item 36. Insummary, the quality of the data was good. (ii)  Rangecoincidence  (possible vs. observable): The observed rangescoincide with what is expected for the minimum value; thesame thing does not happen for the maximum, since thatwould imply patients with very advanced illness andmaximum dysfunction in all the items of the scale.(iii)  Mean and median proximity : Although there is nocriterion that we know of for this, in our sample thedifference was 2.06% in non-fluctuating patients and0.21% in the fluctuators. (iv)  Floor and ceiling effect : Bothin the items and in the totals (for non-fluctuators andfluctuators), this was always less than the suggested 15%[34]. We obtained floor and ceiling effect values between1.1% and 2.8%, both in non-fluctuators and in fluctuators.(v)  Asymmetry : The standard criterion is that this should belocated between  1 and 1 [34]; we obtained values of   0.5(for non-fluctuators) and   0.17 (for fluctuators). 4.2. ReliabilityInternal consistency : in the first evaluation, an  a  valueof 0.88 was reached; in the second, 0.90 (Table 3). ARTICLE IN PRESS Table 1Descriptives of the sampleNo Mean (S.D.) Range Min. Max.No. of patients 131Gender, F/M 39/92Age (years) 68.8 (11) 55 41 96Disease duration (years) 7.8 (5.8) 29.5 0.5 30Years with L-dopa 5.9 (4.7) 22 0 22Dose (mg/day) 767.3 (370.4) 1500 0 1500Pfeiffer 1.7 (1.6) 6 0 6HADSA 9.3 (5.2) 20 1 21D 10.1 (5.1) 21 0 21SPES/SCOPATotal 26.5 (10.6) 48 8 56UPDRS (I. II. III)Total 69.2 (21.6) 100 25 125S&E 66.7 (16.8) 70 20 90PIMS (SI)Non-fluctuators 95 18.4 (7.4) 34 0 34Fluctuators 36 25.3 (5.8) 24 14.5 38.5S.D., standard deviation; SI, summatory index (total).Table 2Hoehn and Yahr staging distributionH&Y 1.5 2 2.5 3 4 and 5No. 6 25 19 70 11Gender F/M 3/3 9/16 5/14 19/51 3/8Age (years) 69.8 (12.2) 62.8 (10.6) 66.2 (8.1) 70.2 (10.7) 77.4 (11.4)Disease duration (years) 1.2 (0.6) 3.6 (2.3) 6.8 (4.1) 9.2 (5.8) 13.1 (7.2)Years with L-dopa 0.2 (0.5) 2.5 (2.3) 4.8 (2.6) 7.2 (4.3) 10.8 (7.2)Dose (mg/day) 208.3 (232.7) 545 (379.9) 750 (138.1) 862.8 (343.8) 1000 (353.5)Pfeiffer 1.3 (1.5) 1.1 (1.1) 0.9 (1.1) 2 (1.6) 3.2 (1.6)HADSA 7.3 (5.8) 6.1 (3.6) 7.4 (4) 10.5 (4.8) 13.7 (7.2)D 8.8 (7.6) 5.8 (4) 9 (3.5) 11.1 (4.4) 16.5 (4.7)SPES/SCOPATotal 12.3 (4.08) 15.8 (5.7) 21.8 (7.01) 29.8 (7.5) 46.1 (2.8)UPDRS (I.II.III)Total 33.6 (8.8) 48.5 (10.8) 59.5 (10.2) 75.3 (12.2) 114 (9)S&E 88.3 (4) 81.6 (6.8) 76.8 (5.8) 63 (10.1) 28.1 (7.5)FluctuatorsNo. 0 1 3 25 7PIMS (SI) 15.5 22.1 (4.9) 24.4 (5.4) 31.6 (5)Non-fluctuatorsNo. 6 24 16 45 4PIMS (SI) 14.3 (11) 12.9 (6.2) 17.1 (5.2) 21.1 (5.8) 30.5 (3.6)Mean values 7 S.D.; SI, summatory index (total). M. Serrano-Duen˜as, S. Serrano / Parkinsonism and Related Disorders 14 (2008) 126–132 128  The test–retest (ICC 95%) ranged from 0.91 (0.87–0.93) foritem 9 up to 0.97 (0.96–0.98) of item 10. The total valuewas 0.98 (0.97–0.98) (Table 4).The PIMS item correlation matrix had its highest valuebetween the Travel and the Safety items (0.751); the lowestvalue was between Community Relationships and Finan-cial Security (0.226) and the mean correlation value was0.450, which was similar to those previously reported[10 – 12]. When grouping the items into four spheres, i.e., Physical (mobility): items 6, 7 and 8; Psychological(emotionality): items 1 and 2; Socialization: items 3, 4 and10; and Economic-Working: items 5 and 9, the correlations(Spearman’s  rho ) were all greater than 0.53. 4.3. Construct validity (i)  Convergent validity  ( Spearman’s rho ): PIMS totalwas properly correlated, with values over 0.6 for the othertools that assess PD and state of mind (HADS; S&E;SPES/SCOPA and UPDRS). The only exception was withthe third section of SPES/SCOPA ( rho  0.57) (Table 5).(ii)  Analysis of ‘‘known groups’’ : (Kruskal–Wallis) thedifferent H&Y stages were properly discriminated, withvalues of   p o 0.0001 (Table 6).When performing analysis by dichotomizing patients intofluctuators and non-fluctuators, depressed and non-depressed,and anxious and non-anxious, PIMS produced values withappropriate confidence intervals that enabled distinguish-ing those groups (Table 7). 4.3.1. Comparison of PIMS with PDQL and PDQ-39 Parkinson’s impact scale was administered in a mean of 10.2 ( 7 1.7)min, compared to a mean of 23 ( 7 2.7)min forPDQ-39 and PDQL.A comparative analysis of internal consistency in PIMS,PDQ-39, and PDQL gave Cronbach  a  values for PIMS of 0.88 and 0.90, less than the 0.96 obtained for PDQ-39and the 0.97 for PDQL (Table 3). As to their qualities(convergent validity) and discrimination of known groups,PIMS obtained results similar to the other two scales(Tables 5 and 6). 5. Discussion As to PIMS psychometric qualities (scale assumptions),all of them are suitable: quality of data, acceptability,internal consistency, reliability, construct validity, andconvergent validity; all of whose values are within rangessimilar to those obtained with PDQ-39 and PDQL. It couldbe argued that the  a  values are discreetly lower, but weshould remember that the value of this coefficient isstrongly influenced by the number of items [37]. Followingthe observation of Schulzer et al. [38], the value of the  a  isin fact similar to the mean of all the possible correlations: a ¼ N   R /([ N   1]  R +1) where  R  is the mean of all the ARTICLE IN PRESS Table 3Internal consistency (Cronbach  alpha )Domains First evaluation Second evaluationMobility (3 items) 0.8727 0.873Emotional (2 items) 0.7842 0.7761Social (3 items) 0.7236 0.6913Work (2 items) 0.6823 0.6024PIMS SI (10 items) 0.8821 0.9015PDQL SI (37 items) 0.9798PDQ-39 SI (39 items) 0.9684SI, summatory index (total); a value at least 0.7 is considered indicative of adequate internal consistency.Table 4Reliability (intraclass correlation coefficients)PIMS (items) 95% ICC9 0.9131 0.8773 0.93854 0.9196 0.8865 0.94315 0.9286 0.899 0.94943 0.9368 0.9107 0.95522 0.9514 0.9313 0.96568 0.9515 0.9315 0.96577 0.9569 0.9392 0.96956 0.9584 0.9412 0.97051 0.9746 0.9642 0.982110 0.9764 0.9666 0.9833SI 0.9837 0.977 0.9885SI, summatory index (total).Table 5Construct validity (convergent rho spearman)PDQ-39 PDQL PIMSAge (years) 0.222   0.237 0.123Disease duration (years) 0.354   0.281 0.325Years with L-dopa 0.210   0.213 0.285Dose (mg/day) 0.510   0.334 0.427Pfeiffer 0.114   0.36 0.284S&E   0.674 0.793   0.74 HADSA  0.668   0.653 0.637 D  0.777   0.782 0.760 SCOPA/SPESA  0.676   0.841 0.723 B  0.747   0.824 0.780 C 0.455   0.71  0.577Total  0.720   0.856 0.772 UPDRSA  0.727   0.767 0.683 B  0.784   0.821 0.739 C  0.688   0.759 0.667 Total  0.745   0.823 0.729 PIMS  0.802   0.896  1Values greater than 0.59 (in bolds) are considered adequate (at level of 0.0001). M. Serrano-Duen˜as, S. Serrano / Parkinsonism and Related Disorders 14 (2008) 126–132  129  correlations and  N   is the number of items on the scale orquestionnaire. Therefore, with 10 items to obtain valuesthat verge on 0.9 compared to values of 0.96 and 0.97obtained on scales of 39 and 37 items—and consideringthat values over 0.7 are accepted for evaluatinggroups [15] —then the PIMS  a  coefficient is suitable andsufficient.It has been pointed out that depressive mood is one of the factors that most affects HRQoL [39 – 43]. Our results on comparing the depressive and non-depressive patientgroups permit us to confirm that fact: the 95% CI(9.2 (7.16  11.42)), which demonstrates the sensitivity of PIMS, in our opinion. In fact—and this is novel as far aswe know—we have also found that in patients with highrates of anxiety, QoL is more affected: the 95% of CI was(7.8 (5.52  10.24)).Fluctuation is a fundamental element in causingdisability and has been pointed out as another elementthat seriously mars the quality of life [39,44]. When comparing the fluctuator and non-fluctuator groups, wefound that the 95% CI was (6.8 (4.07  9.55)). PIMS is theonly specific tool for assessing quality of life in PD thatallows evaluation of this disabling condition of being afluctuator.When analyzing construct validity (convergent validity),PIMS correlated correctly both with UPDRS (sections I–IIIand the total) and with SCOPA/SPES (with three sectionsand the total), which is to say that its validity is solid.The inter-item correlations in the structural matrixshowed values that indicate there is no redundancybetween those items (0.450). When grouped into the fourdomains (psychological, social, physical and economic),they also showed suitable correlations, similar to onesobtained previously (0.440) [10 – 12]. One of the objections to PIMS [14] comes fromconsidering that it does not cover all the spheres that aQoL scale should supposedly include (it certainly does notcover the cognitive aspect, for example). In this respect, it isworth remembering that HRQL questionnaires should belimited in a sense and should not attempt to address everyaspect of life that has an influence on its quality [45]. Onthe other hand, PIMS was the first specific instrument thatevaluated the sexual sphere, without a doubt one of thefundamental aspects of the quality of life construct. It hasrecently been found that the elderly wish for more of a sexlife (understood in a broad sense) than they usually have attheir disposal [46]. Thus, if a Parkinson sufferer experiencesdisability in his daily life (caused by motor dysfunction andfluctuations) and the sexual desire/capacity dysfunctioncharacteristic of the illness or caused by medication [1], it isimportant that the compromising of this dimension betaken into account when evaluating quality of life.Respecting the length of this type of scale, there areexamples of generic QoL measuring tools that are muchshorter than PDQ-39 and PDQL, such as EQ-5D [47] and15D [48], which get suitable psychometric results, similar tothose of the PDQ-39.Parkinson’s impact scale also includes a sphere thatseems of great importance—the work aspect and itsinterrelation with financial matters. This disabling illnesscauses early retirements that involve smaller incomes andat the same time greater expenses, thus producing afinancial imbalance that has received no attention in othertools for measuring the quality of life of Parkinson’ssufferers. The financial dependency often generated isadded to that which the motor impairment causes, and theconsequent role change because of disability is closelylinked with depressive mood which, in turn, itself producesdisability [49] and constitutes a fundamental factor in thedecline of quality of life [39 – 43]. The presence of depression and disability determine to a large degree the ability towork [50], so that this integration of labor and financialaspects with quality of life would seem advisable.The fundamental domains of HRQL scales are based onthe general pattern that Wilson and Cleary [51] proposed,which has had a great influence on the concept of quality of life and can be synthesized as (i) proximal level: biologicaland physiological; and (ii) distal level: the symptoms, theperception of health and, overall, the quality of life. In thisrespect, we should consider that the physical, social, and ARTICLE IN PRESS Table 7PIMS (SI) between groupsMotor Fluctuators Non-fluctuators 95% CI25.3 (5.8) 18.4 (7.4) 6.9 (4.19–9.65)Mood Depressed Non-depressed25.4 (5.9) 16.1 (6.2) 9.2 (7.16–11.42)Anxiety Anxious Non-anxious25.1 (6.2) 17.2 (6.9) 7.8 (5.52–10.24)Mean value 7 S.D; mood and anxiety assessment with HADS (cut scorewas 11/21).Table 6Construct validity (for ‘‘known groups’’ Kruskal–Wallis)H&Y staging1.5 2 2.5 3 4 and 5  p PIMS SI 14.3 (11) 13 (6.2) 17.8 (5.1) 22.2 (5.6) 31.2 (4.4)  o 0.0001PDQ-39 SI 32.7 (31.9) 30.5 (13.4) 41.7 (16.5) 60.6 (23.6) 109 (10.1)  o 0.0001PDQL SI 121 (33.9) 140.8 (15.9) 105.2 (28.5) 103 (20) 58.6 (10.6)  o 0.0001SI, summatory index (total). M. Serrano-Duen˜as, S. Serrano / Parkinsonism and Related Disorders 14 (2008) 126–132 130
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