A short psychosocial questionnaire for patients with Parkinson's disease: the SCOPA-PS

1. Introduction 

Parkinson's disease (PD) is a chronic, progressive, neurologic disorder that affects almost 2% of the population over 65 years of age [1]. The onset of the disease generally occurs between the ages of 50 and 65, and the incidence increases with higher age. PD is characterized by tremor, rigidity, slowness of movement, and abnormalities of posture. Nonmotor features like autonomic dysfunctions, mood changes, and cognitive deterioration often complicate the course of the disease.

Chronic progressive illnesses like PD can have a considerable impact on the psychosocial functioning of patients. Yet in PD, this impact is seldom evaluated separately. The psychosocial consequences of PD are usually assessed with generic or disease-specific health-related quality-of-life (HRQoL) instruments, that include physical items in addition to items that address psychosocial functioning. HRQoL is generally considered to consist of physical, mental, and social (including “role”) aspects of a disease [2]. Item selection in HRQoL scales is usually based on interviews with patients, in which patients are asked to rate the importance of certain features of the disease, and the most relevant items are retained for the final version of the scale. Consequently, HRQoL instruments consist of a mixture of items that only have in common that patients consider them important, and that either physical, mental, or social aspects are evaluated. Additionally, these instruments often include items that address impairment levels and items that address disability levels, which further adds to the heterogeneity. It is often far from clear whether patients interpret certain impairments as being “physical” or “psychosocial.” If, for instance, a patient indicates that he often has trouble with the shaking of his hands, this could mean he experiences trouble with dressing (physical), feels ashamed (psychosocial), or both. Therefore, including items that evaluate the extent to which patients are bothered by impairments, provides no direct insight in the impact this impairment has upon the level of psychosocial functioning. However, the distinction between physical and psychosocial is important. First, separate information on the psychosocial consequences may provide a better understanding of the different consequences of the disease to an individual. Second, neurologists may, because of their professional focus on physical consequences of the disease, interpret particular problems somatically and hence overlook psychosocial difficulties. Third, the distinction between physical and psychosocial consequences may have implications for the choice of an intervention. After all, if the difficulties are predominantly experienced at the physical level, this may call for interventions that aim to improve motor functions, for example, pharmacotherapy or physical therapy. Although people with psychosocial difficulties will also benefit from optimally controlled motor symptoms, additional support from other health care providers, such as psychologists or social workers, may be indicated. To quantify the psychosocial impact of PD, an instrument that only includes items that directly address perceived emotions and experienced difficulties in social situations is needed.

To date, a short, clinimetrically sound scale that evaluates this psychosocial impact of PD is not available. We therefore conducted a study with the objective to develop a short psychosocial instrument for patients with PD, and to evaluate its reliability (internal consistency, test-retest reliability) and validity (construct validity, “known-groups comparisons”).

The development of the SCOPA psychosocial questionnaire (SCOPA-PS) is part of a larger research project, the SCales for Outcomes in PArkinson's disease (SCOPA), in which short, practical, and clinimetric sound scales for all relevant domains in PD are selected or developed.

2. Methods 

3. Results 

One hundred seventy-seven questionnaires (86%) were returned. The characteristics of the patients are presented in Table 1. Mean age and male–female ratio did not differ between responders and nonresponders. However, nonresponders had significantly higher H&Y stages (P = .008) and longer disease duration (12.7 vs. 9.4; P = .017). The first 59 patients were approached for the test-retest analysis. Fifty-four of these patients (92%) returned the SCOPA-PS the second time. The patient characteristics of the retest group were similar to those of the total group.

Table 1. Patient characteristics

	Number of patients	177
	Male/female ratio	99 (56%)/78 (44%)
	Mean age (SD) in years	65.2 (11.1)
	Mean age at onset (SD) in years	55.7 (11.6)
	Mean disease duration (SD) in years	9.4 (5.6)
	Modified Hoehn and Yahr stage	mild (H&Ya 1: 10, H&Y 2: 64): moderate (H&Y 3):	74 (41.8%) 70 (39.5%)
		severe (H&Y 4: 31, H&Y 5: 2):	33 (18.6%)

a Hoehn and Yahr stage.

3.1. Data quality 

None of the items had missing values in more than 5% of the subjects. There were no floor or ceiling effects and all item-total correlations exceeded 0.20 (Table 2).

Table 2. Frequency distribution and item characteristics

	Item no.	Frequency of responses				Valida	Item-totalb	Kwc
	During the past month, have you ..	0	1	2	3
	1 had difficulty with work, household, or other chores?	22	67	60	28	177	0.61	0.69
	2 had difficulty with hobbies, sport, or leisure activities?	20	72	56	29	177	0.59	0.73
	3 felt uncertain in your contact with others?	64	79	30	4	177	0.58	0.50
	4 had problems getting along with your partner, family, or good friends?	122	42	11	2	177	0.34	0.46
	5 had problems in the area of sexuality?	69	44	36	20	169	0.24	0.83
	6 felt more house-bound than you would wish to be?	44	62	47	22	175	0.63	0.73
	7 had the feeling you have had to ask others for help too often?	57	62	40	17	176	0.67	0.61
	8 felt isolated and lonely?	85	64	21	6	176	0.61	0.71
	9 had difficulty when having a conversation?	61	77	30	8	176	0.49	0.55
	10 felt ashamed of your disease?	125	35	12	3	175	0.28	0.65
	11 been concerned about the future?	30	76	51	20	177	0.49	0.68

a Number of valid responses. b Item-total correlations. c Weighted kappa (quadratic weights) for test-retest reliability of individual items.

3.3. Validity 

Correlations between the SCOPA-PS SI on the one hand, and the PDQ-39 SI and PDQ-8 SI, on the other hand, were 0.82 and 0.76, respectively. Correlations of the SCOPA-PS with the HADS, the EQ-5D, and the VAS were somewhat lower and remarkably similar to the correlation of the PDQ-39 with these scales (Table 3). The correlation of the SCOPA-PS SI with the subscales of the PDQ-39 ranged from 0.42 (with the bodily discomfort subscale) to 0.68 (with the emotional well-being subscale). The correlation between both versions of the PDQ was high, which might be expected because the PDQ-8 was derived from the PDQ-39.

Table 3. Correlation between SCOPA-PS and other scales (Spearman's rho)

		PDQ39 SIa	PDQ8 SIa	HADSb	HADS-Ac	HADS-Dd	EQ-5D SIe	VASf
	SCOPA-PS SI	0.82	0.76	0.69	0.61	0.62	−0.61	−0.60
	PDQ39 SI		0.91	0.74	0.69	0.65	−0.69	−0.54
	PDQ8 SI			0.74	0.69	0.64	−0.59	−0.46
	HADS				0.92	0.88	−0.63	−0.58
	HADS-A					0.64	−0.55	−0.49
	HADS-D						−0.58	−0.56
	EQ-5D SI							0.41

NB: all correlations significant (P < .001).

a Parkinson's Disease Questionnaire Summary Index, 39- and 8-item version. b Hospital Anxiety and Depression Scale. c HADS anxiety subscale. d HADS depression subscale. e Euroqol summary index. f Visual analog scale assessing quality of life.

The mean duration between the H&Y assessments and the time of the survey was 3.5 months. Because patients in H&Y stages 1 and 5 were underrepresented (10 and 2 patients, respectively), disease severity was categorized as mild (H&Y 1 and 2), moderate (H&Y 3), or severe (H&Y 4 and 5). Ordinal logistic regression yielded a good fitting model (chi-square 45.9, degrees of freedom 46; P = .48) displaying a significant increase in psychosocial disability with increasing H&Y stages (P < .001). The mean SCOPA SI of mildly affected patients was 25.7 (SD = 12.7), whereas for moderately and severely affected patients this was 37.2 (SD = 18.7) and 45.1 (SD = 18.5), respectively. Ordinal logistic regression of the SCOPA-PS SI on the scores of the anxiety/depression item of the EQ-5D also displayed a good fitting model (chi-square 37.5, degrees of freedom 48; P = .86) indicating a significant increase in psychosocial disability with higher anxiety/depression scores (P < .001). The mean SCOPA-SI of patients scoring 1 (no problem), 2 (some difficulty), or 3 (extreme difficulty) on this item of the EQ-5D were 26.5 (SD = 14.6), 41.1 (SD = 17.0), and 63.0 (SD = 9.2), respectively.

The SCOPA-PS SI correlated significantly with disease duration (rs = 0.20; P < .01), but not with age (rs = 0.02; P = .78). No significant difference in SI was observed between male and female patients.

4. Discussion 

We have developed a short questionnaire that evaluates psychosocial functioning in patients with PD. The response rate in this study was high and the quality of the data was good. Patients that participated in this study attended an outpatient movement disorders clinic in the western part of The Netherlands. This clinic has a regional function and serves patients with a wide range of disease severities in PD.

The internal consistency and retest reliability of the SCOPA-PS SI were good, and convergent validity with other scales agreed with our expectations. “Known-groups” comparisons indicate that patients with longer disease duration, higher disease severity, and elevated levels of anxiety and depression have significantly higher SCOPA-PS scores. Age and sex are not related to worse outcomes. Although the nonresponse rate in our study was low, the SCOPA-PS scores may actually have been somewhat higher, because nonresponders had higher disease severity and longer disease duration, both of which variables were related to higher SCOPA-PS scores.

The use of this scale on an individual level is somewhat disputable. The minimum threshold for reliability in group comparisons is often set at 0.70, whereas for use on the individual level, generally more stringent demands are made. Nunnally and Bernstein [19] state that for important decisions on an individual level, a reliability of 0.90 is the minimum. Helmstadter [20] quotes variable reliability values for various types of psychological tests intended for individuals, the median for personality tests being 0.85, that for ability tests being 0.90, and for attitude tests, 0.79. Hays et al. [21] state that the 0.90 criterion for individual assessment may be too stringent, and that many highly regarded instruments fail to meet this standard. Because the SCOPA-PS is not intended for diagnostic purposes (that could involve important decisions for individuals based on the patient's score in relation to a cutoff level), the demands for internal consistency may be somewhat less stringent. We believe that the scale can adequately be used for monitoring psychosocial functioning over time, and may serve as an indicator of areas of potential problems.

All items of the scale had item-total correlations that exceeded the predefined criterion. However, some items had moderate item-total correlations and will be discussed in more detail. This concerned item 4 (getting along with partner, family, or good friends), item 5 (problems with sexuality) and item 10 (felt ashamed) with values of 0.32, 0.24, and 0.28, respectively. We did not consider to remove one or more of these items, because in our view test characteristics of items should not dominate the item selection process at the expense of content validity. In this so-called clinimetric approach, it is important that all relevant attributes of the construct are measured, and hence, content validity and reproducibility are the most important parameters [22].

The moderate item-total correlation for item 4 (getting along with partner, family, or good friends) is most likely explained by the low endorsement of this item. To examine whether this may have been the result of the way this item was framed, we evaluated five different versions of this item in 30 patients after the postal survey had been completed. However, no differences between these versions were found, and we therefore decided to retain the original description. Our findings regarding this item are supported by observations from various studies on the PDQ-39, in which the “social support” subscale consistently has been found to produce the lowest mean score, both in clinic and nonclinic samples, and across populations from different countries 6, 9, 14, 23, 24. This subscale also shows the lowest correlations with measures of disease severity 6, 9, 14, 25, indicating that progression of the disease does not greatly affect the quality of close relationships.

The pattern of correlations and endorsement frequencies of item 10 (felt ashamed) is very similar to that of item 4 (problems getting along with partner, family, or good friends). Seventy-one percent of the patients indicated no problems with respect to this item. In several studies this item showed low item means 6, 14, 23, 24, 26, and its correlation with measures of disease severity were also moderate (range 0.29–0.33) 6, 14, 23, 24, 26.

The moderate item-total correlation of the item on sexuality may be explained by physical features of the disease, especially with respect to male patients. Problems with erectile function may affect up to 60% of males [27], while on the other hand anti-Parkinsonian medication may increase libido. Female patients more often report vaginal tightness and involuntary urination, which may affect the quality of the sexual relationship [28]. Evidently, these physical problems do not necessarily correlate highly with other psychosocial consequences of the disease. Although the origin of the problems may be physical, the consequences for the psychosocial level are considerable, and consequently, an item addressing this topic should be present in a psychosocial instrument. A large proportion of our patients (59%) indicated problems in this area. Men had significantly higher scores than women (item means 1.40 vs. 0.56, respectively; P < .001), but the severity of the sexual problems did not correlate significantly with disease severity or age.

Several disease-specific HRQoL instruments have become available in PD in the past few years 5, 6, 7, 9, 29, 30 (see for a review Marinus et al [3]). These scales include items on physical, mental, and social aspects of the disease. The instruments usually inquire how often patients had difficulty with certain aspects of the disease, and often include both impairments and disabilities. As far as the impairments are concerned, it is not always clear whether these difficulties are of a physical or a psychosocial nature. We therefore propose to disentangle these levels by using separate instruments to assess physical and psychosocial functions. These separate measures may produce more meaningful and conceptually clear indices. Instruments that assess physical disabilities in PD already exist 31, 32, 33, but to date, a short scale that evaluates the psychosocial consequences of PD is not available.

One could argue that the separate subscales of the two most frequently used disease-specific HRQoL scales in PD, the PDQ-39 [6] and the Parkinson's Disease Quality-of-Life questionnaire (PDQL) [5], may be used, because the PDQ-39 has subscales on emotional well-being, stigma, social support, and communication, whereas the PDQL has both a social and an emotional subscale. Apart from the fact that it is unusual to use only subscales of an instrument and that the involved subscales of both instruments would still consist of 16 items each, other arguments favor the use of the SCOPA-PS. As far as the PDQ-39 is concerned, both internal consistency and test-retest reliability of the social support subscale have been found to be low (Cronbach's α and Pearson's r < 0.7) in some studies 6, 34, whereas role functioning is only marginally addressed and sexuality is not addressed at all in this scale [3]. The PDQL on the other hand, provides no information on two important psychosocial items, viz. close relationships and role functioning.

If the basic assumption is to select a short disease-specific instrument, the SCOPA-PS may be preferred over the other currently available short HRQoL instruments, the Parkinson's Impact Scale (PIMS, 10 items) [29] and the PDQ-8 [9], because of the potential problems with respect to content validity of these scales. The items in the PIMS were obtained by consensus between specialized nurses and did not involve patients in the item generation phase. The PDQ-8 was obtained through statistical procedures in which the item with the highest item-total correlation in each of the eight subscales of the PDQ-39 was selected for the short version. This approach may lead to a scale that does not reflect the content of the original scale adequately. In the PDQ-8 engagement in work, household, and leisure activities is not assessed, while items on sexuality and role functioning are also lacking. Furthermore, the internal consistency of the PDQ-8 was somewhat low in our study (Cronbach's α 0.74).

Taken together, the SCOPA-PS fills the need for a short, clinimetrically sound scale. It addresses the difficulties patients experience in social and emotional spheres. The scale can adequately be used in research situations, whereas the use in clinical practice may be argued. The internal consistency is, however, similar to that of comparable subscales of other disease-specific HRQoL instruments in PD. The distinction between physical difficulties on the one hand and emotional and social difficulties on the other hand, provides a clear insight in the difficulties patients perceive in the two distinct domains.