Quality of Life Research 12: 635–644, 2003. 2003 Kluwer Academic Publishers. Printed in the Netherlands.
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Health-related quality of life in patients with systemic lupus erythematosus: Development and validation of a lupus specific symptom checklist C. Grootscholten1, G. Ligtenberg2, R.H.W.M. Derksen3, K.M.G. Schreurs4, J.W. de Glas-Vos5, E.C. Hagen6, A.W.L. van den Wall Bake7, T.W.J. Huizinga8, F.H.J. van den Hoogen9, M. Bijl10, J.C. van Houwelingen11, F.J. Snoek12 & J.H.M. Berden13 1 Division of Nephrology, University Medical Center, Nijmegen (E-mail:
[email protected]); 2 Division of Nephrology, University Medical Center; 3Department of Rheumatology and Clinical Immunology, University Medical Center; 4Division of Clinical and Health Psychology, Utrecht University, Utrecht; 5 Division of Nephrology, Academic Medical Center, Amsterdam; 6Division of Internal Medicine, Eemland Hospital, Amersfoort; 7Division of Internal Medicine, St. Joseph Hospital, Veldhoven; 8Division of Rheumatology, Leiden University Medical Center, Leiden; 9Division of Rheumatology, University Medical Center, Nijmegen; 10Department of Internal Medicine, Division of Clinical Immunology, University Hospital, Groningen; 11Division of Medical Statistics, Leiden University Medical Center, Leiden; 12Division of Medical Psychology, VU University Medical Center, Amsterdam; 13Division of Nephrology, University Medical Center, Nijmegen Accepted in revised form 12 September 2002
Abstract Reliable and sensitive measures are needed to evaluate the quality of life (QoL) in patients with systemic lupus erythematosus (SLE). No lupus specific questionnaires are available. This study describes the development and validation of a disease-specific questionnaire for lupus patients, which assesses the presence and burden of 38 disease- and treatment-related symptoms: the SLE Symptom Checklist (SSC). Reliability and reproducibility were tested in respectively 87 and 28 stable SLE patients. The internal consistency (Cronbach’s a coefficients 0.89) and test–retest reliability (Pearson product–moment correlation coefficient between 0.67 and 0.87) were satisfactory. Concurrent validity was supported by significant, but moderate correlations with other measures of subjective well-being and functional status. Responsiveness was measured in 17 patients with lupus nephritis treated with cyclophosphamide, at start of therapy and 1 year thereafter. A significant change in number of symptoms and total distress level was found. It is concluded that the SSC has satisfactory psychometric properties and appears suitable for both clinical and research purposes. Key words: Health status, Systemic Lupus Erythematosus, Quality of life, Questionnaire, Validation Abbreviations: ACR – American College of Rheumatology; AIMS – Arthritis Impact Measurement Scales; FSS – Fatigue Severity Scale; HAQ – Health Assessment Questionnaire; IRGL – Influence of Rheumatic Diseases on General Health and Lifestyle; MOS-SF-20 – Medical Outcomes Study Short Form 20; MOSSF-36 – Medical Outcomes Study Short Form 36; POMS – Profile of Mood States; QoL – Quality of Life; QOLS – Quality of Life Scale; SLE – Systemic Lupus Erythematosus; SLEDAI – SLE Disease Activity Index; SSC – SLE Symptom Checklist; VAS – Visual Analogue Scale
636 Introduction Systemic lupus erythematosus (SLE) is an autoimmune disease in which autoantibodies are formed to a large variety of self-antigens. It affects many organs (skin, joints, kidney, heart, brain). Therefore, clinical symptoms are broad and variable in severity. The cause and cure of this chronic life-long disease with remissions and exacerbations remain unknown. Its incidence is highest in young women. In clinical management and research of SLE patients, objective parameters are used to describe disease activity and treatment efficacy. In addition, aspects of subjective quality of life (QoL) are important to assess, in order to determine perceived health status and treatment burden [1– 7]. More so, disease and treatment related morbidity have increased in SLE as a result of improved therapeutic options and a related decrease in mortality rates [8–12]. Therefore, reliable and practical measures are needed to evaluate the perceived QoL in patients with SLE. To our knowledge, no lupus specific QoL questionnaires have been described in the literature, although adapted versions of the quality of life scale (QOLS) [13–15] and the arthritis impact measurement scale (AIMS) [2] have been used. Also, several studies have been conducted in SLE patients with generic QoL questionnaires such as the Medical Outcomes Study Short Forms 20 and 36 (MOS-SF-20 [16, 17] and MOS-SF-36) [6, 18–21] and the Health Assessment Questionnaire (HAQ [22, 23]). In addition, the Fatigue Severity Scale (FSS), a symptom-specific questionnaire, was studied in patients with SLE [24–26]. But as fatigue is not the only symptom in lupus patients this scale will not give insight in other symptoms. It has been advocated, that disease-specific questionnaires should be included in QoL research, as they are more sensitive to changes than generic instruments [27], and appropriate to evaluate specific therapeutic interventions in clinical trials [28]. Testa et al. [28] used a theoretical model in which experienced symptoms are regarded as an important aspect of the physical domain of the multi-dimensional QoL spectrum. We therefore decided to develop and validate a disease-specific, subjective outcome measure for SLE patients, to be used in addition to generic QoL measures. In this article we report on the SLE
Symptom Checklist (SSC) and its performance in Dutch patients.
Methods Item selection and reduction Items for this Dutch questionnaire were solicited from the literature. In addition, physicians treating SLE patients were asked to generate items they thought were relevant in evaluating treatment efficacy in lupus patients. The items could be related to the disease itself and/or to treatment given. After panel discussion the chosen items were reviewed by 20 lupus patients who marked the items regarded as most intrusive, and further items were added. Another 10 SLE patients were interviewed for review of the item list and were invited to add missing items. This led to the formulation of 38 items, included in the SSC (see Appendix for the English translation of the SSC). The SSC was designed as a self-administered questionnaire, similar to for example the Diabetes Symptom Checklist [29], and to be filled out in less than 10 min. First, the subject is asked whether or not a symptom has occurred in the past month. Second, if the symptom occurred, the subject is asked to rate the perceived burden of that symptom, on a four-point Likert scale, ranging from ‘not burdensome’ (¼1) to ‘extremely burdensome’ (¼4). The SSC identifies the number of symptoms that have occurred in the past 4 weeks (score 0–38). In addition, the subjective burden (total SLE symptom distress score) can be calculated by summation of the perceived burden of all items endorsed (score 0– 152). Additional instruments Physicians were asked to calculate a SLEDAI (SLE Disease Activity Index) [30] score, and a visual analogue scale (VAS) score for subjective assessment of disease activity (physician’s VAS). A lower score (range 0–10) denotes less disease activity. Socio-demographic and medical information from the patients was obtained from a short selfadministered questionnaire, comprising 16 questions addressing sex, age, duration of lupus, use of medication, and other variables.
637 Perceived general health status was measured by a VAS with the following question: ‘Everything considered, how do you feel at this moment?’. The scale ranges from 1 to 10, a higher number representing a higher degree of general well being (patient’s VAS). To assess the impact of SLE on activities of daily life, we used an adapted version of the Influence of Rheumatic diseases on General health and Lifestyle (IRGL) questionnaire [31], which is based on the AIMS [32]. The IRGL has been validated in the Netherlands for rheumatoid arthritis patients [31]. For the present study only the IRGL subscales ‘mobility’ and ‘impact of disease’ were applied. The mobility part consists of six items measuring activities such as walking stairs. The impact of disease on daily life is evaluated by 10 items. For all questions, the answers range on a four-point Likert scale from ‘almost never’ to ‘almost always’. The internal consistency coefficients for these two subscales tested in 362 Dutch patients with rheumatoid arthritis were 0.92 and 0.87, respectively [31]. The experienced treatment burden was measured using the following two questions: ‘The treatment so far was…’, on a fivepoint Likert scale ranging from ‘not burdensome’ to ‘extremely burdensome’ and ‘What aspect of the treatment did you experience as most burdensome?’, as an open end question. Emotional well-being was assessed with the Dutch shortened version of the Profile of Mood States (POMS) [33–35]. It consists of 32 items with a fivepoint response format, ranging from ‘not at all’ to ‘extremely’. It contains five mood scales: ‘depression’, ‘anger’, ‘fatigue’, ‘tension’, and ‘vigour’. The internal consistency coefficients of the five subscales, described in the literature, range from 0.84 to 0.91 in 491 Dutch women and from 0.82 to 0.91 in 481 Dutch men [33]. A positive correlation between negative mood states with the number of symptoms as well as subjective burden was expected. The widely used MOS-SF-36 was added as a generic QoL measure [20, 36–39] in a sub-group of patients (see below). The SF-36 has been tested in patients with SLE [6, 18, 20, 39] and was recommended to be used in SLE patients [40, 41]. The SF36 contains eight domains (‘physical functioning’, ‘role limitations: physical problems’, ‘bodily pain’, ‘general health perception’, ‘vitality’, ‘social func-
tioning’, ‘role limitations: emotional problems’ and ‘mental health’) and one question pertaining to change in health (‘reported health transition’). After recoding, all eight scales can reach a maximum of 100, with a higher number representing better functioning and/or less limitations. The internal consistency, studied in a Dutch population sample (691 females and 372 males), ranged from 0.71 (‘social functioning’) to 0.93 (‘bodily pain’), with a mean and median of 0.85 [38]. All patient instruments were self-administered. Study samples Between January and June 1995, 100 consecutive lupus patients with stable disease, not involved in the initial development of the SSC, in five university out-patient clinics for nephrology or rheumatology, were asked to fill out the questionnaires. All patients fulfilled at least four American College of Rheumatology (ACR) criteria for SLE [42]. The questionnaires were handed out at regular visits and the patients were asked to return or send them to the physician with a prepaid and pre-addressed envelope. Response rate was 87%; nearly all questionnaires were filled out completely. This patient group will be referred to as group I and will be used for the analysis of internal consistency and validity. Another sample (group II) of 40 stable patients was asked to complete the forms twice, with an interval of 1 month. These patients were recruited from the out-patient clinics of two university medical centres at the departments of nephrology or rheumatology. From 28 patients (70%) two properly completed questionnaires were received, which could be used for analysis of reproducibility. Thirty-three patients returned one or more questionnaires (83%); these questionnaires were used for study correlations with SF-36. The responsiveness of the SSC was analysed in 17 proliferative lupus nephritis patients who were receiving cyclophosphamide pulse therapy (group III). Questionnaires filled out at start and after 1 year of therapy were analysed to study changes in symptom frequency and symptom distress. It is difficult to define an effect size statistically. Moreover, a clinical relevant difference is also difficult to define, since the patient’s experience and adaptation plays an important role.
638 Thus, group 1 filled out all QoL instruments except for the SF-36. The other two groups were asked to complete all instruments including the SF-36. Comparisons of SF-36 scores were done in patients from group II and III. All available questionnaires were used, but only one questionnaire per patient. In case of lupus nephritis (group III) the available questionnaires filled out at start of cyclophosphamide therapy were used. Analysis could be done in 33 questionnaires from group II and in 14 questionnaires from patients with active lupus nephritis (group III).
correlations were expected. Low correlations were expected between SLEDAI and SSC (r between 0.10 and 0.30). Pearson correlation coefficients were also used to analyse reproducibility. Coefficients of at least 0.60 were considered acceptable. In the responsiveness analysis, Wilcoxon rank tests were used for testing differences. A p-value 10 years (%)
Group I
Group II
p
87 82 (94) 32.5 (20–71) 96 (12–360) 49 (55) 33 (38) 50 (57) 38 (44) 27 (31)
33 29 (88) 37.0 (18–64) 110 (12–312) 17 (52) 14 (42) 21 (64) 18 (55) 7 (21)
NS NS NS NS NS NS NS NS
Analysis for internal consistency and validity was performed in group I. Reproducibility was tested in 28 patients from group II (in those who completed two questionnaires).
639 Table 2. Frequency and distress of the most frequently reported symptoms in 87 stable SLE patients (group I) Symptom
Frequency (%) Symptom distressa (1–4) ± SD
Fatigue Painful joints Painful muscles Loss of concentration Headache Mood changes Spontaneous bruises Muscle weakness Sensitivity to sunlight Disturbed memory ‘White’ fingers in cold weather
77 53 47 47 46 45 47 39 38 37 37
(89) (61) (54) (54) (53) (52) (54) (45) (44) (43) (43)
2.7 2.4 2.4 2.4 2.4 2.4 1.9 2.5 2.7 2.7 2.5
± ± ± ± ± ± ± ± ± ± ±
0.9 0.7 0.6 0.6 0.9 0.7 0.6 0.8 1.0 0.9 0.9
a Perceived burden of the symptom, measured on a four-point Likert scale ranging from 1 = ‘not burdensome’ to 4 = ‘extremely burdensome’.
letal complaints. Mental symptoms, as loss of concentration, changes of mood and a disturbed memory were relatively frequently mentioned as well. Reported to occur less frequently, but equally burdensome as fatigue, were ‘sensitivity to sunlight’ and ‘disturbed memory’. The mean score on the patient’s VAS was 6.4 (range 1.6–10, scale 1– 10). For the SSC the Cronbach’s a was 0.89, which indicates good homogeneity (Table 3). The Cronbach’s a did not change by leaving out each item one by one, indicating that each of the items was relevant for this scale. Although conceptually included, explorative factor analysis did not yield two separate dimensions, i.e. ‘disease-related’ symptoms and ‘therapy-related’ symptoms. The physician’s assessment of disease activity, whether measured by the SLEDAI-score (median 4.0, interquartile range 1–6) or by the physician’s VAS (median 1.5, interquartile range 0–2), was
significantly, but weakly correlated with the number of symptoms (r ¼ 0:30 and r ¼ 0:31) and total distress level reported by the patients (for both r ¼ 0:26). Other subjective measurements of the impact of disease on daily life and mood were however not related with the physician’s ratings. Notably, the patient’s global assessment (patient’s VAS) was not correlated with SLEDAI or physician’s VAS. For the IRGL and POMS Cronbach’s a’s were examined and are mentioned here since this is the first time these instruments were tested in SLE patients. The IRGL subscales ‘impact on mobility’ and ‘impact on daily life’ showed Cronbach’s a’s of 0.92 and 0.88, respectively. For the five mood scales of the POMS the internal consistency coefficient ranged from 0.75 to 0.94. Concurrent validity of the SSC was supported by the significant correlations between the impact of disease on the one hand (from adapted IRGL), and impact of treatment, number and distress level of symptoms, and the four negative mood scales of the POMS on the other. A significant negative correlation existed between impact of disease and the patient’s VAS of general health. Mobility was negatively correlated with age, duration of SLE, impact of disease, number and distress of symptoms, and the mood scales ‘depression’, ‘fatigue’ and ‘tension’. Table 4 shows a correlation matrix of the SSC and other QoL instruments. High correlations were found between the number of symptoms and total distress level (r ¼ 0:94). Therefore only the total symptom distress level is given in Table 4. A correlation matrix of the SSC and the MOSSF-36 in 47 questionnaires from 47 SLE patients is presented in Table 5 (group II and III). Among these 47 patients were 33 stable SLE patients from group II and 14 patients with active lupus nephritis
Table 3. Reliability of the SSC in patients with stable lupus Subscale SSC
Number of symptoms Total distress level a
Internal consistency (group I) N ¼ 87
Test-retest reliability (group II) N ¼ 28
Items
Mean
SD
a
Correlationb
Mean of difference
38 38
12.9 30.1
7.6 19.2
0.89 0.89
0.78* 0.87*
)0.2 )2.6
Cronbach’s a; b Pearson’s correlation coefficient. * p < 0:001:
a
640 Table 4. Correlation matrix for QoL and disease activity instruments in 87 stable SLE patients (group I)
Total distress level Patient’s VAS Physician’s VAS SLEDAI
IRGL IRGL mobility disease impact
Treatment impact
POMS POMS depression anger
POMS fatigue
POMS tension
POMS vigour
Patient’s Physician’s SLEDAI VAS VAS
)0.54* )0.53* )0.17 )0.12
0.28 )0.05 )0.03 )0.01
0.60* )0.58* 0.10 0.08
0.69* )0.65* 0.04 0.07
0.58* 0.45* )0.04 0.04
)0.25 0.55* 0.02 0.03
)0.54*
0.55* )0.48* 0.08 0.03
0.51* )0.41* )0.02 )0.05
0.26 )0.21
0.26 )0.14 0.75*
* p < 0:001.
Table 5. Correlation between SSC and MOS-SF-36 in 47 patients (33 stable patients from group II and 14 patients with active lupus nephritis before start of therapy, from group III)
Table 6. Change in SSC scores and patient’s VAS between start and 12 months after start of cyclophosphamide therapy for proliferative lupus nephritis (group III, N = 17)
SSC total distress level Physical functioning Role-physical Bodily pain General health Vitality Social functioning Role-emotional Mental health Reported health transition
0.56* 0.57* 0.44* 0.44* 0.57* 0.46* 0.66* 0.45* þ0.01
* p < 0:01.
at start of cyclophosphamide therapy (group III). Low to moderate negative correlations are seen with all MOS-SF-36 domains, except between SSC total symptom distress level and ‘reported health transition’. Extra support for the SSCs concurrent validity is provided with these data. The ‘general health’ domain of the MOS-SF-36 was the only domain to change significantly in the lupus nephritis group (group III), with an increase from 37 to 45. No significant differences were seen in the other MOS-SF-36 domains after 1 year. Reproducibility (group II) The SSC Pearson correlations coefficient in 28 stable patients, who completed two questionnaires with a 1-month-interval, was 0.78 for the number of symptoms, and 0.87 for the total distress level (Table 3). This supports the short-term stability of the SSC. The correlation coefficient for patient’s
Start of therapy for nephritis SSC Number of symptoms 13.6 Total distress level 33.7 Patient’s VAS 6.2
Change after SD of 1 year of difference therapy
2.9* 9.2* þ0.4
5.1 14.9 1.3
* p < 0:05.
VAS was 0.67. No distinct trends over time were seen (data not shown). Sensitivity to change (group III) Comparison of means (and differences of means) for SSC, in the group of lupus nephritis patients receiving cyclophosphamide treatment, showed significant changes in the number of symptoms and in total distress level, while no change was found in patient’s VAS. Results are summarised in Table 6. Strikingly, the number of symptoms and the total distress level at start of cyclophosphamide therapy in patients with active lupus nephritis were not different from the group of stable SLE patients.
Discussion The data from our study support the validity of the newly developed SSC, a Dutch self-report
641 questionnaire comprising 38 symptoms, which were identified as relevant to health-related QoL by both specialised physicians and patients. The disease specificity of the measure may provide important additional information regarding the patient’s subjective health status, and can help detect significant changes in well-being, in relation to therapeutic interventions [27, 28]. Furthermore, instead of just counting the number of symptoms, the grading of the burden per symptom makes it possible to make a difference between having a symptom which is not experienced as burdensome and not having the symptom at all. With this approach smaller changes which might be important for the patient can be detected. Internal consistency of the SSC was high. Factor analysis did not yield distinct dimensions, suggesting that the two conceptual dimensions (i.e. lupus-related symptoms and therapy-related symptoms) are not reflected in the patient’s experience. Reproducibility tests in stable patients with a 1-month-interval showed acceptable correlation coefficients. Although a day-to-day difference in experiencing burden of symptoms is present in every person and a 1-month-interval is quite a long period of time, no distinct trends were seen. Concurrent validity was supported by the finding that significant but moderate correlations with other QoL instruments were found, underscoring the fact that the SSC provides unique information. The SSC did detect changes in lupus nephritis patients who received cyclophosphamide therapy, comparing symptoms at start of therapy with those after 1 year of therapy. Although our data are promising the sensitivity to change needs to be studied in a larger group of patients. In line with our expectations, only one domain of the MOS-SF36 changed significantly after 1 year of therapy, supporting the importance of adding a diseasespecific measure. The patient’s VAS did not show significant differences after 1 year, which may be explained by the short period of time (cyclophosphamide pulse therapy is given during a period of 2 years). Notably, the SSC score in patients with prolifera-
tive nephritis at start of therapy did not differ from that in groups of stable SLE patients. Apparently, patients experience no difference in general well-being and symptoms while having active renal disease. This psychological adaptation, has been found in several groups of patients with chronic diseases. Patients tend to adapt cognitively to changes in their physical health [44]. We do realise that our data have not demonstrated discriminant validity of the SSC and this remains to be determined in future studies with more patients. Although this study is only a first validation in quite small groups, our data are very promising. And, since it is a Dutch questionnaire cross-cultural validation will be needed for use in other countries and languages. In our stable SLE patients the most frequently scored symptoms were fatigue, musculoskeletal complaints and mental symptoms. Fatigue is the most common, and most debilitating symptom, as was shown previously [22, 24, 45–47]. Most studies [22, 46, 47] do not find a correlation between the physician’s assessment of disease activity and the severity of fatigue. The objective parameter for disease activity (SLEDAI) and the physician’s VAS correlated only weakly with the total number of symptoms and the total distress level, but did not correlate with the patients global assessment for general well-being (patient’s VAS). These observations are consistent with other studies [13, 16, 26, 48], supporting the use of both subjective and objective indices. In conclusion, the SSC is a brief, easy to administer disease specific QoL instrument that may prove useful, both for clinical and research purposes.
Acknowledgements This study was supported by grants from the Dutch Kidney Foundation (C94.1363), the Dutch League against Rheumatism (project no. 735) and The Netherlands Organisation for Scientific Research (NWO 920-03-115).
642 Appendix 1 English version of SSC No (0)
Did you, in the past month, have… Painful joints Painful muscles Headache Fatigue Ulcers in mouth or throat Hair loss Skin rash Red and painful eyes Pain while breathing Shortness of breath ‘White’ fingers in cold weather Itch Ankle oedema Chubby cheeks/face More appetite Less appetite Pimples Facial hair growth Blue/purple stretch marks on the skin Spontaneous bruises Poor wound healing Muscle weakness Blurred vision Nightmares Mood changes Nausea/vomiting Stomach complaints Sensitivity to sunlight Sensitivity to artificial light Fits Fainting Genital sores Chest pain Loss of concentration Muscle cramps Vulnerable skin Disturbed memory Weight gain
( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( (
) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) )
Yes (1)
( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( (
) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) )
If yes, how burdensome
fi fi fi fi fi fi fi fi fi fi fi fi fi fi fi fi fi fi fi fi fi fi fi fi fi fi fi fi fi fi fi fi fi fi fi fi fi fi
Not (1)
A little (2)
Quite (3)
Extremely (4)
( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( (
( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( (
( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( (
( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( (
) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) )
) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) )
) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) )
) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) )
Do you have other symptoms? If yes, please specify…
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Address for correspondence: C. Grootscholten, Division of Nephrology (545), Department of Medicine, University Medical Center, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands Phone: þ31-24-3614761; Fax: þ31-24-3540022 E-mail:
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