COMPASS 31: A Refined and Abbreviated Composite Autonomic Symptom Score

Abstract

Objective

To develop a concise and statistically robust instrument to assess autonomic symptoms that provides clinically relevant scores of autonomic symptom severity based on the well-established 169-item Autonomic Symptom Profile (ASP) and its validated 84-question scoring instrument, the Composite Autonomic Symptom Score (COMPASS).

Patients and Methods

We assessed the internal consistency of COMPASS using Cronbach α coefficients based on the ASP of 405 healthy control subjects recruited and seen in the Mayo Clinic Autonomic Disorders Center between March 1, 1995, and March 31, 2010. Applying a simplified scoring algorithm, we then used exploratory factor analysis with orthogonal rotation and eigenvalue calculations to extract internally consistent domains and to reduce dimensionality. This analysis was followed by expert revisions to eliminate redundant content and to retain clinically important questions and final assessment of the new instrument.

Results

The new simplified scoring algorithm alone resulted in higher Cronbach α values in all domains. Factor analysis revealed 7 domains with a total of 54 questions retained. Expert revisions resulted in further reduction of questions and domains with a remaining total of 31 questions in 6 domains (COMPASS 31). Measures of internal consistency were much improved compared to those for COMPASS. Following appropriate weighting, this instrument provides an autonomic symptom score from 0 to 100.

Conclusion

COMPASS 31 is a refined, internally consistent, and markedly abbreviated quantitative measure of autonomic symptoms. It is based on the original ASP and COMPASS, applies a much simplified scoring algorithm, and is suitable for widespread use in autonomic research and practice.

The Autonomic Symptom Profile (ASP) is a well-established questionnaire designed to comprehensively evaluate the severity and distribution of symptoms and the autonomic functional capacity of patients with autonomic disorders. It comprises 169 questions and assesses 11 domains of autonomic function.¹ It was first described by Suarez et al¹ in 1999, continues to be used routinely at Mayo Clinic and many other institutions around the world for a comprehensive assessment of autonomic symptoms and functions, and continues to serve this purpose very well.

Using a limited set of 84 clinically selected questions, we have used this questionnaire to generate a Composite Autonomic Symptom Score (COMPASS).¹ The questions comprising this instrument address 11 autonomic domains with 72 questions (orthostatic intolerance, 9 items; secretomotor, 8 items; male sexual dysfunction, 8 items; urinary, 3 items; gastroparesis, 5 items; constipation, 4 items; diarrhea, 4 items; pupillomotor, 7 items; vasomotor, 11 items; reflex syncope, 5 items; and sleep, 8 items) and an additional 12 items to generate 2 validity scores (an understatement index comprising 6 questions and a psychosomatic index comprising 6 questions).¹ It has been validated and used extensively by our group and selected others.^1-7

However, over the years, we have identified several problems with this instrument that have resulted in concerns about supporting this tool for use by other institutions in spite of broad national and international interest:

• 1The scoring algorithm of COMPASS is highly complicated and requires computer analysis for score generation. The complexity and ambiguity of the extraction process has resulted in even experienced users obtaining inconsistent scores.
• 2Completion of the ASP, even if limited to the questions relevant for COMPASS, is time consuming.
• 3The questions within the domains assessed using COMPASS have not been evaluated for internal consistency.
• 4Several questions included in the original COMPASS instrument have over time been identified to be less meaningful or redundant for scoring autonomic function and symptom severity.

A redesign of this instrument to a simplified, more time-efficient, statistically more robust, but still comprehensive tool to assess and grade symptoms relevant to autonomic function that can find broad application in research and clinical practice is therefore needed. The specific aims of this study were (1) to develop a simplified and more user-friendly scoring scheme for questions that comprise COMPASS and (2) to critically assess current questions and domains and use state-of-the-art statistical methods guided by clinical judgment to develop an updated, concise, and statistically robust stand-alone tool that provides a clinically relevant general score of autonomic symptom severity with meaningful subscores for individual autonomic domains.

Patients and Methods

Study Participants

A total of 405 healthy control subjects who were recruited and seen in the Mayo Clinic Autonomic Disorders Center between March 1, 1995, and March 31, 2010, were asked to complete the ASP after informed consent was obtained. The study was reviewed and approved by the Mayo Clinic Institutional Review Board.

New Scoring Scheme

A new, simplified autonomic symptom scoring scheme was developed that follows a homogeneous pattern of scoring throughout the instrument. Simple yes or no questions were scored as 0 points for no and 1 point for yes. Questions about a specific site of symptoms or symptoms under specific circumstances were scored as 0 if not present and as 1 if present for each site or circumstance. All questions regarding the frequency of symptoms were scored as 0 points for rarely or never, 1 point for occasionally or sometimes, 2 points for frequently or “a lot of the time,” and 3 points for almost always or constantly. All questions regarding the severity of symptoms were scored as 1 point for mild, 2 points for moderate, and 3 points for severe. When assessing the time course of a symptom, we scored 0 points for responses such as “gotten somewhat better,” “gotten much better,” “completely gone,” and “I have not had any of these symptoms,” 1 point for “stayed about the same,” 2 points for “gotten somewhat worse,” and 3 points for “gotten much worse.” The scores for changes in bodily functions depended on the individual question asked. For example, “I get full a lot more quickly than I used to when eating a meal” was scored 2 points and “I get full a lot less quickly than I used to” was scored 0 points, while the answer “I sweat much more than I used to” was given 1 point and “I sweat much less than I used to” was scored 2 points.

For the new scoring system, we opted to eliminate scoring of questions previously comprising the syncope domain because of its vast overlap with the orthostatic domain and the questionable relevance of reflex syncope for the assessment of autonomic deficits.⁸ We also eliminated questions about male erectile dysfunction for scoring because of the low specificity of erectile dysfunction as an indicator of autonomic nervous system impairment and the difficulty of a universal scoring system with questions that relate only to one gender.^9,10 Furthermore, we opted to combine the diarrhea domain and the constipation domain into a single lower gastrointestinal domain.

Statistical Approach to Assessing the New Scoring Scheme

Comparisons of the current scoring algorithm using the questions originally selected for COMPASS with the previously described new scoring algorithm using all suitable questions from the ASP was performed by calculating Cronbach α coefficient as a measure of internal consistency for items comprising respective domains as they are grouped in the current version of the ASP.^11,12 A Cronbach α coefficient of 0.70 or higher was considered acceptable.

Factor Analysis and Approach to Content Reduction

In order to identify internally consistent question domains and to reduce dimensionality, ie, the number of questions retained, unbiased exploratory factor analysis of items was performed with orthogonal rotation.^11-13 The eigenvalue rule was used to extract factors, retaining only factors with eigenvalues greater than 1. The resulting model was confirmed by inspecting the corresponding scree plot, which is a visual representation of where the sharp decline in factors levels off, at which point factors become less relevant (even if their eigenvalues are >1). Only items with factor loading of 0.40 or greater were retained, and ambiguous items (ie, items loading on more than one factor) were eliminated.

The resulting set of questions and domains was then reviewed by 2 autonomic experts (P.A.L., W.S.) to accomplish the following 3 goals: (1) to decide on redundant content in order to allow for further reduction in the number of questions, (2) to retain clinically important questions that were previously eliminated on factor analysis, and (3) to assess for clinical appropriateness of the grouping of questions into domains based on the factor analysis.

Final Assessment of Content and Design of the New Instrument

After clinical review and revision of questions and domains to be included in the final symptom score, another calculation of Cronbach α coefficient values was performed to assess for the internal consistency of the new instrument. To allow for the calculation of a weighted total score, the maximum raw score for each domain was determined and each domain was assigned a weight factor based on our current perception of the importance of domains for reflecting autonomic failure, so that the minimal weighted score for the instrument equals 0 and the maximum weighted score equals 100. All the analyses were performed using SAS version 9.2 software (SAS Inc).

Results

Study Participants

Of the 405 recruited control subjects, 166 (41%) were male and 239 (59%) were female. Ages ranged from 8 to 79 years with a median age of 32 years. Race was predominately white (388; 95.8%), and ethnicity was predominantly non-Hispanic or Latino (394; 97.3%).

Comparison of Scoring Schemes Using the Previous COMPASS Domains

The Cronbach α coefficient of previous COMPASS domains ranged from −0.89 to 0.79 using the old scoring system, with only 2 domains reaching a value above 0.70 (orthostatic intolerance and erectile dysfunction). Cronbach α coefficient values were markedly improved using the new scoring system, ranging from 0.40 to 0.90, with 4 domains reaching a Cronbach α coefficient greater than 0.70 (Table 1). All domains had a higher Cronbach α coefficient with the new compared to the old scoring system. Cronbach α coefficient calculations stratified by gender showed a similar trend with markedly improved values for both males and females using the new scoring algorithm (Table 1).

TABLE 1.

Comparison of Internal Consistency of the Previously Used Domains Using Old and New COMPASS Scoring Algorithms^a

Domain	COMPASS—previous scoring algorithm				COMPASS—new scoring algorithm
		Cronbach α coefficient				Cronbach α coefficient
	No. of items	All (405)	Females (239)	Males (166)	No. of items	All (405)	Females (239)	Males (166)
Orthostatic intolerance	9	0.79	0.79	0.78	28	0.90	0.91	0.88
Vasomotor	11	0.68	0.69	0.57	11	0.84	0.85	0.80
Secretomotor	8	0.34	0.28	0.42	13	0.52	0.55	0.44
Gastroparesis	5	0.50	0.52	0.35	7	0.66	0.69	0.56
Constipation	4	−0.32	−0.33	−0.22	10b	0.82b	0.81b	0.85b
Diarrhea	4	−0.89	−0.95	−0.82
Bladder	3	0.53	0.42	0.74	3	0.58	0.48	0.74
Pupillomotor	7	0.55	0.57	0.47	11	0.87	0.86	0.88
Sleep	8	0.36	0.31	0.39	8	0.40	0.44	0.33
Syncope	5	0.13	−0.01	0.36	NA	NA	NA	NA
Male erectile dysfunction	8	0.75	NA	0.75	NA	NA	NA	NA
Total	72				91

^aNA = not applicable.

^bConstipation and diarrhea domains were combined.

Exploratory Factor Analysis

Exploratory factor analysis based on the eigenvalue rule and factor-loading criteria described previously identified 7 factors consisting of a total of 54 questions. Five of these 7 factors corresponded well with the previous domains of orthostatic intolerance, vasomotor, secretomotor, pupillomotor, and bladder, each containing only items that had previously been part of those domains. The other 2 factors grouped questions on gastroparesis and diarrhea as 1 factor (a mixed upper gastrointestinal domain) and questions regarding constipation as a separate factor. The Cronbach α coefficient for these domains ranged from 0.71 to 0.93 and therefore exceeded the acceptable level of 0.70 for each of these 7 domains (Table 2). The previous sleep domain was not identified as a separate factor of internal consistency and was therefore eliminated.

TABLE 2.

Domains Identified, Cronbach α Coefficients, and Number of Questions Retained Within Each Domain Based Solely on Statistical Measures (Exploratory Factor Analysis) With Factor Loading ≥0.40^a

Domains	Cronbach α coefficient	No. of questions
Orthostatic intolerance	0.93	17
Vasomotor	0.91	9
Secretomotor	0.71	4
Gastrointestinal—mixed upper and diarrhea	0.87	8
Constipation	0.89	4
Bladder	0.79	2
Pupillomotor	0.90	10

^aIncludes all 405 study subjects.

Expert Revisions and Final Assessment of Content

Expert review confirmed the grouping of items into 7 factors as clinically meaningful domains with content that allows for retaining previous clinical designation of domains. It was believed, however, that retaining a separation between a gastroparesis/diarrhea domain and a constipation domain was not clinically useful, and the 2 gastrointestinal domains were combined, resulting in a total of 6 autonomic domains in the new instrument.

Review for redundant content allowed for elimination of 23 more items. Both experts believed that 5 items that were originally not retained in the factor analysis should be reinstated because of their clinical importance. These factors consisted of questions about changes in body sweating, dryness of the mouth, postprandial vomiting, cramping/colicky abdominal pain, and loss of bladder control.

The remaining 31 items and new scoring method were reanalyzed for Cronbach α coefficient of each domain. Compared to the statistically ideal 54-question set, Cronbach α coefficient values were similar for 3 of the 6 domains, slightly lower but still high for the gastrointestinal domain, and lower (and below 0.70) for the other 2 domains (0.62 for the bladder domain and 0.48 for the secretomotor domain) (Table 3), which was expected because these domains include items with low factor loading that were retained on the basis of clinical importance alone. The Cronbach α coefficient for each domain was still notably higher than those for the original comparable domains within COMPASS. Table 3 delineates the 6 new domains, the number of questions per domain, and the maximum weighted scores of the new instrument. The original ASP is provided in Supplemental Appendix 1, the COMPASS 31 instrument is provided in Supplemental Appendix 2, the scoring system is shown in Supplemental Appendix 3 (Supplemental Appendixes are available online at http://www.mayoclinicproceedings.org, linked to this article), and the weight factors for calculating weighted scores are listed in Table 3.

TABLE 3.

Domains and Number of Questions Retained Based on Exploratory Factor Analysis and Clinical Revisions as Used in the Final Instrument (COMPASS 31)^a

Domain	No. of questions	Max raw score	Weighting factor	Max weighted score	Cronbach α
Orthostatic intolerance	4	10	4.0	40	0.92
Vasomotor	3	6	0.83333333	5	0.91
Secretomotor	4	7	2.1428571	15	0.48
Gastrointestinalb	12	28	0.8928571	25	0.78
Bladder	3	9	1.1111111	10	0.62
Pupillomotor	5	15	0.3333333	5	0.84
Total	31	75		100

^aAppropriate weighting factors for each domain result in appropriately balanced autonomic domains and a total score between 0 and 100. Max = maximum.

^bCombines former constipation, diarrhea, and gastroparesis domains into one domain.

Discussion

Using statistical measures and clinical autonomic expertise, we designed a new, refined, and abbreviated composite autonomic symptom score, the COMPASS 31. The need to develop this new instrument arose from problems with the old COMPASS instrument and the critical need for a straightforward, up-to-date, and broadly applicable self-assessment tool that can assess and quantify autonomic symptom severity across multiple autonomic domains.

Since its original description and validation, we have used the original COMPASS in many autonomic research studies and trials.^2-7 It has been an exceedingly helpful addition to our repertoire to assess autonomic nervous system function and to this point remains the only validated instrument assessing multiple domains of autonomic function. Other more recently developed instruments are helpful but are limited to specific domains.^14,15 We regularly receive requests to support the use of COMPASS by other groups and institutions, but for a number of reasons, we have been hesitant to do so.

First, we have seen inconsistencies and frank errors in scoring with this instrument, even among experienced users. There is little doubt that this relates to the highly complicated scoring algorithm that requires dedicated computer analysis for reliable score generation. Second, several questions included in the original COMPASS instrument have been identified over time as less meaningful or redundant for scoring autonomic function and symptom severity. Third, completion of the ASP, even if limited to the questions relevant for COMPASS, is time consuming. Finally, the questions within the domains assessed using COMPASS have never been evaluated for internal consistency.

When developing COMPASS 31, we sought to address each of these concerns. As a first step, we made considerable changes to the scoring algorithm by applying a much simplified, consistent scoring scheme. This new scoring scheme is more user friendly and also resulted in notably improved measures of internal consistency. Using exploratory factor analysis and critical clinical review of all questions included in the original ASP, we identified 6 internally consistent and meaningful clinical autonomic domains. With the exception of 5 questions that were retained on the basis of clinical importance alone, we retained only questions that fulfilled both preidentified statistical and relevance criteria. Redundancies were reduced as much as possible. As a final step, we assigned each domain a weighting factor based on the relevance of each domain for assessing autonomic function, with factors adjusted so that the minimum total score is 0 and the maximum score is 100. The result is an instrument with considerably improved measures of internal consistency across all domains and with an easily interpretable score of autonomic symptom severity.

COMPASS 31 does not include assessment of erectile dysfunction. Some may view this as a shortcoming of this instrument, but we decided a priori to exclude this domain for several reasons. Erectile dysfunction is a common accompaniment of aging, with prevalence rates as high as 52% in 40- to 70-year-old men.⁹ Many factors contribute to erectile dysfunction, including psychological, hormonal, vascular, and neurologic factors. Erectile dysfunction as the result of medication adverse effects is common.¹⁰ Although erectile dysfunction certainly may reflect autonomic dysfunction, we believe that because of its nonspecific nature, erectile dysfunction should not be included in an autonomic severity score. These symptoms should be elicited during a comprehensive autonomic symptom assessment via direct patient interview or by using the ASP, which is designed for that purpose. Finally, the old version of COMPASS was associated with difficulties in statistics and reporting of group results because of the difference in maximum scores between genders related to the male-specific extra domain; these problems are now resolved with the new instrument.

Another domain eliminated for scoring was the syncope domain. There was considerable overlap with the orthostatic intolerance domain, and questions related to reflex syncope were not considered to be a meaningful measure of autonomic dysfunction.⁸ Questions previously comprising the sleep domain were found to have very low internal consistency and were not identified as an independent domain in our factor analysis. We did not think that retaining this domain could be justified on the basis of clinical relevance alone.

Our previous separation of the gastrointestinal domain into gastroparesis, constipation, and diarrhea domains was not maintained by factor analysis. The analysis suggested an advantage in grouping questions related to gastroparesis and diarrhea into one domain and questions related to constipation in a second domain. We believe that such grouping would be artificial and that the future users of the instrument would be better served by providing a single gastrointestinal domain score akin to the single score for all the other domains. If further discrimination is needed, this could be achieved by review of individual questions.

Conclusion

The COMPASS 31 was developed as a self-assessment instrument of autonomic symptoms and function that is up-to-date, broadly applicable, easy to administer in a short amount of time, and based on a scientific approach. It was designed to provide a global autonomic severity score and domain scores that are both clinically and scientifically meaningful. We believe that these goals have been achieved. Further validation of this new instrument in various autonomic disorders and degrees of autonomic failure is now in progress.

COMPASS 31 is based on the well-established ASP, a comprehensive questionnaire assessing autonomic symptoms across multiple domains. All questions in COMPASS 31 are contained in the ASP. It is, therefore, easily possible to derive a COMPASS 31 score either from the comprehensive ASP or from the 31 selected questions that comprise the COMPASS 31 instrument, depending on the goals of the clinician or investigator. The new instrument is compatible with data previously acquired using the ASP.

We have included the complete instrument and tools necessary for its application and score generation in this publication. It is our hope that COMPASS 31 will be embraced by many autonomic clinicians and researchers as a concise quantitative measure of autonomic symptoms and function and that it will find broad application in clinical autonomic research and practice.