development of a symptom severity index and a symptom impact index for stress incontinence in women

Neurourology and Urodynamics 15:630-640 (1996)

Development of a Symptom Severity Index and a Symptom Impact Index for Stress Incontinence in Women Nick Black, Joanne Griff iths, and Catherine Pope

Health Services Research Unit, Depaflment of Public Health and Policy, London School of Hygiene and Tropical Medicine, London, England

Stress incontinence is a common problem among women, yet there is no adequately validated instrument for measuring women’s views of its severity (disease-specific health status). The only instrument for measuring the impact or bothersomeness of symptoms (disease-specific quality of life) has poor internal consistency. This paper describes the development and psychometric assessment of two new indexes, a Symptom Severity Index and a Symptom Impact Index. Following several qualitative enquiries, a questionnaire was developed and administered to 442 women undergoing stress incontinence surgery. The face and content validity of the items comprising the indexes was good. The Severity Index (0-20) showed good variability (median 14, interquartile range 6) and adequate internal consistency (alpha 0.76). The Impact Index (0-12) also had good variability (median 5 , interquartile range 3 S ) and internal consistency (alpha 0.80). Convergent and discriminant validity were demonstrated for both indexes. Test-retest reliability was high. While responsiveness is still to be tested, the two indexes are psychometrically strong and can be used to measure the severity and impact of stress incontinence in women. 0 1996 Wiley-Liss, Inc.

Key words: index, symptom severity, symptom impact, stress incontinence, gynourology

INTRODUCTION

Evaluation of the treatment of stress incontinence in women requires valid, reliable, and acceptable indexes that measure women’s perceptions of the severity of their symptoms and the extent to which their symptoms affect their lives. Although the need for such measures has been recognized for some time [Cardozo, 19801, relatively little attention has been paid to this issue, given the estimated prevalence of the problem.

Attempts to measure women’s views of the seventy of their symptoms have

Received for publication May 13, 1996; accepted July 5, 1996.

Address reprint requests to Nick Black, Health Services Research Unit, Department of Public Health and Policy, London School of Hygiene and Tropical Medicine, Keppel Street, London WClE 7HT, England. We thank all the women who participated in the study; their surgeons, for providing access; Jenny Stanley, for help in administering the survey; Donna Lamping, for psychometric advice; and the Medical Research Council, for funding.

0 1996 Wiley-Liss, Inc.

Symptom Indexes for Stress Incontinence 631

consisted of surgeons’ assigning a grade based on a clinical history of incontinence: grade 1-only on coughing or sneezing; grade 2-on walking or running; grade 3-at all times [Ingelman-Sundberg, 1951; Fowler, 19861. Another, slightly more sophisticated measure distinguished 4 levels of severity for incontinence (provoked by coughing, fast movements, walking, and standing up) and also considered the frequency of use of protective pads (never, sometimes, most of the time) [Kujansuu, et al., 19851. These questions on symptom severity were combined, however, with 2 on the impact of the symptoms, thus confusing the issue. Two other measures of symptom severity were based on the frequency of incontinence (3 or 4 levels), the amount lost (2 or 3 levels) and (in one of these measures) the use of protective pads [Norton, 1982; Sandvik, 19931. None of these methods, however, was subjected to psychometric testing.

In contrast to the meager study of symptom severity, there has been some work undertaken on developing an index for measuring the impact of incontinence symptoms on women’s lives. Based on some earlier preliminaq work in the United Kingdom [Norton, 19821, the Continence Program for Women Research Group in the United States developed an Incontinence Impact Questionnaire [Wyman, 19871. This is not specific to stress incontinence but covers all types. During psychometric testing, 2 indexes were developed, one based on how bothersome symptoms were (Uro- genital Distress) and one on the effect of incontinence on travel, social life, emotional life, and physical activities (Incontinence Impact) [Shumaker, 19941. Each index was based on 50 questions and was derived from data from a rather unrepresentative sample (of well-educated women of middle to high socioeconomic status), and for each the internal consistency of the subscale for stress incontinence was poor (Cron- bach’s alpha 0.48). Although others are currently developing measures of symptom impact, these are either for all types of incontinence [Wagner, 19951 or for urge incontinence only [Marquis, 19951.

Given the lack of appropriate instruments, our objective was to develop self- report symptom severity and symptom impact indexes for stress incontinence.

METHODS

Draft questions for assessing symptom severity and impact were devised based on a review of questionnaires from other relevant studies, observation of 35 outpatient consultations, and in-depth interviews with 10 women suffering from stress incontinence. The interviews were largely unstructured but sought to cover each respondent’s experience of incontinence, how it had affected her life, and how she currently coped on a day-to-day basis. Interviews lasted 45 to 120 minutes.

In a pilot study, draft questionnaires were tested on 21 women to check for comprehensibility, ambiguity, and redundancy. Each woman has asked to complete the questionnaire and encouraged to seek clarification from the interviewer, when necessary. The interviewer then went through the questionnaire with the respondent to ensure that the written responses corresponded to those obtained in discussion. General comments about the questionnaire were also sought. As a result, several changes were made to the content and wording of the questions (see Appendix for details). To obtain information on the long-term continence status of respondents, most of the questions referred to their experiences over the previous year rather than the previous few weeks or months. In addition to symptom severity and impact,

632 Black et al.

TABLE I. Sociodemographic Characteristics of Women Undergoing Surgery for Stress Incontinence (n = 442)

Age (years) 40 or less 41-50 51-60 61-70 71 or more

Social class ProfessionaUrnanagerial Skilled Semi and unskilled Missinglnot applicable

Age completed full-time education (years) 16 or under

19 or over Missing

17-18

Employment status Working full-time Working part-time Housewife Retiredlunable to work Unemployed Missing

Marital status Maniedlcohabiting Singlelwidowedldivorced Missing

Housing tenure Owner-occupier Private rental Public rental Missing

Number

69 144 132 65 32

77 158 87

121

296 76 37 33

135 100 66

117 11 13

342 98 2

305 30

103 4

15.6 32.6 29.9 14.7 7.2

24.0 49.2 26.8

72.4 18.6 9.0

31.5 23.5 15.4 27.3 2.6

77.7 22.3

69.6 6.8

23.5

questions covered sociodemographic factors, past medical and obstetric history, co- existent conditions, mental health, and expectations of surgery.

The revised questionnaire was administered to 442 women before they underwent surgery for stress incontinence in one of 18 hospitals in the North Thames region of England between January 1993 and June 1994. Women were excluded if they were unable to read and understand English. Women were recruited by the ward nursing staff during their stay in the hospital. Just over 60% of the women were between 41 and 60 years of age (Table I). The distributions of social factors fairly reflected characteristics in the general population of women of similar age.

To obtain further information on the face and content validity of the questionnaire, a random sample of 36 women were visited at home during the month before their admission to hospital for surgery. As in the pilot phase, each woman was asked to complete a questionnaire, after which the interviewer went through it with her. The


TABLE 11. Construction of Symptom Severity Index

score

Item 0 1 2 3 4

Occurrence of wetting or leaking urine Never 1-4 a month 2-4 a week 1 a day >1 a day Amount/volume usually leaked - A few drops A small amount A cupful Floods No. of padsfsanitary towels used None 1-3 a week 4-6 a week 1-4 a day >4 a day No. of activities that precipitate incontinence None 1-3 4-5 6 -7 8 -9 No. of days leaked in Dast week None 1-3 4-5 5 -6 7

criterion for inclusion for any question was at least 80% agreement for accuracy, clarity, and appropriateness. Any question not reaching this standard would be altered or dropped.

In order to construct the indexes, all items are required to have the same range of responses so that each question contributes equally to the index score. This is desirable, unless there is evidence to suggest that some items are of greater impor- tance than others. Such evidence does not currently exist. For the Symptom Severity Index, the fourth item (number of activities that precipitate incontinence) was made up of 9 dichotomous variables; the last 5 had a “not applicable” response available for women who were physically impaired not necessarily as a result of incontinence. Those who answered “yes” were given a score of 1, while a “no” or “not applicable” scored 0, giving a range of 0 to 9. The internal reliability of this subscale was acceptable (Cronbach’s alpha 0.78). The subscale was divided into five categories (0, 1-3,4-5,6-7, and 8-9) so that it could be added to the other 4 items in the Symptom Severity Index. The responses to 2 other items were also manipulated into 5 categories (Table 11). The Symptom Impact Index was constructed from 4 items (Table 111). The fourth item, on the effects of symptoms on activities, was based on the proportion of applicable activities affected.

The psychometric properties of both indexes were examined in several ways. First, the internal consistency of the items was assessed using Cronbach’s alpha [Cronbach, 195 11. Next, sensitivity and specificity were assessed. Sensitivity, known as convergent validity in the context of index development, requires evidence that the index correlates well with factors known or thought to be related. In this instance, 2 factors were believed to be associated with symptom severity-a woman’s body mass index, and her having undergone previous surgery for stress incontinence.

Specificity, or discriminant validity, is tested by seeking evidence of a lack of association with variables believed to be unconnected with symptom severity or impact. The literature suggested this was true for the following: age, social class, age upon finishing full-time education, housing tenure, smoking status, length of stress incontinence history, parity index, and comorbidity [Black, 19961. Continuous variables (age, parity index, and length of history) were assessed using linear regression, while associations with categorical variables were tested using chi-squared and chi- squared tests for trends.

634 Black et al.

TABLE 111. Construction of Symptom Impact Index

Score

Item 0 1 2 3 4

1 Avoiding activities due to worrying about leaking Never Few times Half the time Most of the time Always

2 Avoiding activities due to needing a toilet Never Few times Half the time Most of the time Always

3 Number of other worries None 1 2 3 4 4 Proportion of activities

affected None 1-40 41-60 61-99 100

Finally the test-retest reliability was assessed. Fifty women (not included in the cohort described above) who had undergone stress incontinence surgery 12 to 18 months previously were mailed the final versions of the 2 indexes (Appendix). On receipt of the completed test questionnaire, each was sent a second “retest” copy. The level of concordance was assessed.

RESULTS Face and Content Validity

As a consequence of women’s comments during the piloting of the draft questionnaire, several changes were made to improve the face and content validity. This seems to have been successful in that there was little missing data from the 442 respondents. For the 5 items in the Severity Index, the proportions of missing data were 0, 0.5, 2.7, 0.5, and 3.8%. For the 4 items in the Impact Index, missing data comprised 2.7, 2.2, 1.1, and 2.9%. While 49 women (11%) took the opportunity to provide qualitative comments on their experiences, these comments did not introduce any aspects of severity or impact that were not already covered by the items included in the indexes. Finally, the home interviews with 36 of the 442 women confirmed that there was a high level of comprehension of the questions and all major aspects of severity and impact were covered.

Distribution of Item and Index Scores

The distribution of item scores for the Severity Index are shown in Table IV. The resulting distribution of index scores was 0-4 (19; 4.6%); 5-8 (56; 13.5%); 9-12 (104; 25.0%); 13-16 (134; 32.2%); and 17-20 (103; 24.8%). The median was 14, with an interquartile range of 6. As expected, the distribution is skewed toward the higher end of the scale, given that the respondents were undergoing surgery for stress incontinence.

The distribution of item scores for the Impact Index are shown in Table V. The resulting distribution of Index scores was 0 (14; 3.4%); 1-4 (122; 29.4%); 5-8 (126; 30.4%); 9-12 (116; 28.0%); and 13-16 (37; 8.9%). The median was 7, with an interquartile range of 6.

Reliability

The internal consistency of the Severity Index was acceptable, given the small number of items available (Cronbach’s alpha 0.76). It was not improved by


TABLE IV. Distribution of Item Scores for Symptom Severity Index

score

Item 0 1 2 3 4

How often do you wet or leak urine? (n = 442) 0 57 (12.9) 57 (12.9) 52 (11.8) 276 (62.4) Amountlvolume usually leaked (n = 440) 0 67 (15.2) 231 (54.1) 119 (27.0) 16 (3.6) Pad/sanitary towel usage (n = 430) 97 (22.6) 49 (11.4) 24 (5.6) 216 (50.2) 44 (10.4) The number of activities that precipitate incontinence (n = 440) 16 (3.6) 88 (20.0) 95 (21.6) 152 (34.5) 89 (20.2) Number of days leaked in past week (n = 425) 27 (6.4) 92 (21.6) 56 (13.2) 31 (7.3) 219 (51.5)

TABLE V. Distribution of Item Scores for Symptom Impact Index

Score

Item 0 1 2 3 4 ~~ ~ ~ ~

1 Avoiding activities due to worrying about leaking (n = 430) 128 (29.8) 140 (32.6) 51 (11.9) 75 (17.4) 36 (8.4)

2 Avoiding activities due to needing a toilet (n = 432) 176 (40.7) 129 (29.9) 48 (11.1) 57 (13.2) 22 (5.1)

(n = 437) 29 (6.6) 84 (19.2) 124 (28.4) 114 (26.1) 86 (19.7)

affected (n = 429) 103 (24.0) 107 (24.9) 31 (7.2) 68 (15.9) 120 (28.0)

3 Number of other womes

4 Proportion of activities

removing any of the items (Table VI). In contrast, the internal consistency of the Impact Index (Cronbach’s alpha 0.7681) was improved by removing the item “Num- ber of other worries” (alpha 0.8). The frequency distribution of the new index with just three items was 0 (62; 14.8%); 1-4 (174; 36.8%); 5-8 (134; 32.0%); and 9-12 (68; 16.3%). The distribution was slightly skewed to the lower end of the scale, with a median of 4 and an interquartile range of 6.

Convergent Validity

Symptom Severity was associated with body mass index (P < 0.0001) and the chi-squared test for trend was also significant (P = 0.001). There was a marked increase in the proportion of women with severity scores of 17 to 20 with increasing obesity (Table VII). Severity was also significantly associated with a woman’s having undergone previous surgery for stress incontinence (P = 0.001): 77.2% reported severity scores of 13 to 20, as compared with 52.2% of women who had no history of previous surgery. The Symptom Impact Index was also associated with body mass index (P = 0.001) and the chi-squared test for trend was significant (P = 0.008). Symptom impact was not, however, associated with previous surgery.

636 Black et al.

TABLE VI. Internal Consistency of Symptom Severity Index and Symptom Impact Index

Corrected item-total Alpha if correlation item deleted

Symptom Seventy Index Frequency of leaking in past year 0.60 0.69 Usual amount/volume of leakage 0.42 0.75 Padhanitary towel usage 0.59 0.69 Number of activities that precipitate incontinence 0.43 0.75 Days leaked in past week 0.64 0.67

Avoiding activities due to wonying about leaking 0.68 0.65 Avoiding activities due to needing a toilet 0.66 0.66 Number of other womes 0.37 0.80 Proportion of activities affected 0.59 0.70

Symptom Impact Index

TABLE VII. Relationship Between Symptom Severity Index and Body Mass Index (n = 3961

Seventv Index ~ ~~~~~

B M I (kg/m2) 1-4 5-8 9-12 13-16 17-20 Total

25 or less 9 32 36 48 27 I52

25-30 9 17 38 57 36 157

over 30 1 5 22 23 36 87

(5.9) (21.1) (23.7) (31.6) (17.8) (100)

(5.7) (10.8) (24.2) (36.3) (22.9) (100)

(1.2) (5.8) (25.3) (26.4) (41.4) (100)

Discriminant Validity

No significant correlations were found between symptom severity and any of the following: age (R = -0.05, P = 0.4); length of history of stress incontinence (R = 0.07, P = 0.2); parity index (R = -0.1, P = 0.06); social class (P = 0.38); age upon finishing full-time education (P = 0.6); housing tenure (P = 0.68); smoking status (P = 0.67); and comorbidity (P = 0.06).

No significant correlations were found between symptom impact and any of the following: length in history of stress incontinence (R = 0.02, P = 0.79); parity index (R = -0.05, P = 0.36); social class (P = 0.67); age upon finishing full-time education (P = 0.2); smoking status (P = 0.14); and comorbidity. There was evidence of correlation with age (R = -0.16, P = 0.0008) and housing tenure (P = O.OOO1). Women in rented housing were more likely to score 8 or more (54.9% versus 21.5%), while owner-occupiers were more likely to score 4 or less (63.6% versus 52.2%).

Test-Retest Reliability

Of the 49 women who received a questionnaire (one was sent to the wrong address), 40 (82%) replied. Of these, 31 (78%) completed and returned a second questionnaire. Responders were older (mean age 56 versus 49.2 years; P = 0.048)


TABLE VIII. Intra-Rater Reliability: Difference in Index Scores Between Test and Retest Questionnaires (n = 31)

Difference in scores Symptom Seventy Index Symptom Impact Index

None 11 (36.7) 24 (82.8) One 4 (13.3) 2 (6.9) Two 9 (30.0) 2 (6.9) Three 5 (16.7) 1 (3.4) Four 1 (3.3) -

Missing 1 2 30 (100%) 29 (100%)

but similar with regard to socioeconomic status (P = 0.15), educational level (P = 0.12), and housing tenure (P = 0.23). Most women (65%) returned the second questionnaire within 2 weeks of having returned the first. The rest took up to 5 weeks. Of the 31 respondents, 30 answered all items in the Symptom Severity Index and 29 answered all items in the Symptom Impact Index.

The symptom seventy retest scores were similar (? 2) to the test scores for 24 (80%) respondents (Table VIII). Of the 6 women with discordance greater than 2, 4 gave widely differing responses for the item on leaking urine during the past week. In addition, 4 of these 6 women took 2 to 5 weeks to return the second questionnaire. Discordance may therefore reflect a real change in symptom seventy rather than a lack of test-retest reliability.

The symptom impact scores were even more frequently concordant (Table VIII). For 26 (90%) women the retest scores were within 2 points of the initial score. There was no apparent reason for discordance in the 3 other respondents, though 2 of them also had discordant symptom severity scores.

DISCUSSION

Valid, reliable, and acceptable instruments for assessing the severity of stress incontinence and its impact on women’s lives were successfully developed. The 2 indexes have been shown to have good face and content validity, to have adequate variability, to be internally consistent, to possess convergent and discriminant validity, and to have good test-retest reliability [SACMOT, 19951. In addition, testing the final versions on a small population sample suggested they were acceptable to potential recipients. The only recommended change to be made to the instruments tested (Appendix) is the exclusion of “Number of worries” from the Symptom Impact Index.

The only attribute that has not been examined so far is the responsiveness of the indexes. This will be done using longitudinal outcome data on the cohort of 442 women who underwent stress incontinence surgery and were referred to in this paper. Results will be reported in a subsequent paper.

The lack of standard validated instruments for measuring the severity of stress incontinence has severely limited scientific research on this condition. This is one reason why the quality of the literature that evaluates the effectiveness of surgical treatments is poor [Black, 19961. The indexes presented here are a first step in the development of accurate measures of symptom severity and impact. As with any instrument, improvements in them can be made as data are accumulated from their

638 Black et al.

use. Testing of the indexes was obviously limited by the data available. For example, as more is learned about the factors associated (or not associated) with symptom severity, the rigor of testing convergent (and discriminant) validity can be enhanced. One aspect in particular that needs investigation is the performance of the indexes when questions relate to a recall period shorter than one year.

CONCLUSIONS

While the current version of our instrument is not perfect, it does provide researchers and clinicians with a means of obtaining accurate measures of severity and symptom impact. Meanwhile, further work is needed to try to enhance the current version.

REFERENCES Black NA, Downs SH (1996): The effectiveness of surgery for stress incontinence in women: a systematic

Cardozo L, Stanton SL (1980): Genuine stress incontinence and detrusor instability: a review of 200

Cronbach LJ (1951): Coefficient alpha and the internal structure of tests. Psychometrika 16:297-334. Fowler JE (1986): Experience with suprapubic vesicourethral suspension and endoscopic suspension of

the vesical neck for stress urinary incontinence in females. Surg Gynecol Obstet 162:437-441. Ingelman-Sundberg A (1951): Urinary incontinence in women, excluding fistulas. Acta Obstet Gynecol

Kujansuu E, Wirta P, Yla-Outinen A (1985): Quantification of urethral closure function by SUI threshold after pubococcygeal sling operation. Ann Chir Gynaecol 74 (Suppl 197): 19-22.

Marquis P, Amarenco G, Sapede C, Josserand F, Jacquetin B, Richard F (1995): Development and validation of a disease-specific quality of life questionnaire for urinary urge incontinency (abstract). Qual Life Res 4:458-459.

review. Brit J Urol (in press).

patients. Brit J Obstet Gynaecol 87:184-190.

Stand 31:266-291.

Norton C (1982): The effects of urinary incontinence in women. Int Rehab Med 4:9-14. SACMOT (Scientific Advisory Committee of Medical Outcomes Trust) (1995): Instrument review cri-

teria. Medical Outcomes Trust Bulletin 3 (4):;-iv. Sandvik H, Hunskaar S, Seim A, Hermstad R, Vanvik A, Bratt H (1993): Validation of a severity index

in female urinary incontinence and its implementation in an epidemiological survey. J Epidemiol Comm Health 47:497-499.

Shumaker SA, Wyman JF, Uebersax JS, McClish D, Fantl JA (1994): Health-related quality of life measures for women with urinary incontinence: the Incontinence Impact Questionnaire and the Uro- genital Distress Inventory. Qual Life Res 3:291-306.

Wagner TH, Patrick DL, Bavendam TG, Martin ML, Buesching DP (1995): Quality of life of people with urinary incontinence: development of a new measure (abstract). Qual Life Res 4:501.

Wyman JF, Harkins SW, Choi SC, Taylor JR, Fantl JA (1987): Psychosocial impact of urinary incontinence in women. Obstet Gynecol 70:378-381.


APPENDIX Symptom Severity Index

These questions ask about your usual symptoms over the past year. 1 How often do you wet or leak urine?

[ ] More than once a day [ ] Once a day [ ] 2-4 times a week [ ] Once a week [ ] 2-4 times a month [ ] Once a month [ ] Never.

2 How would you describe the amount of urine you usually leak? [ 3 Damp/a few drops [ ] Wet/a small amount [ ] Quite wetkupful (i.e., soaks a padhanitary towel) [ 3 Very wet/floods How many pads or sanitary towels do you use?

How many times per day?

3

1-3 4-6 1-2

[ I [ I [ I [ I

4 Do you ever wet or leak urine on . . . ?

None a week a week a day

Coughing Sneezing Laughing Getting out of bed Climbing stairs or steps Lifting something (like heavy shopping bags) Physical activity (like rushing to catch a bus) Keeping fit/Sports activity Sexual intercourse

3-4 a day [ I

Yes [ I [ I [ I [ I [ I [ I [ I [ I [ I

5 In the past week how often have you leaked urine?

Not at A few About half Most all days the week days [ I [ I [ I [ I

5 or more a day [ I

Not applicable [ I [ I [ I [ I [ I

Every day [ I

Symptom Impact Index

1 How often do you not do some activity (like a hobby, or going out) because you are worried about wetting yourself or leaking?

A few About half Most of Never times of the time the time Always [ I [ I [ I [ I [ I

640 Black et al.

2 How often do you not do some activity (e.g., going out with friends, shopping, etc.) because you are worried about needing a toilet?

A few About half Most of Never times of the time the time Always

[ I [ I [ I [ I [ I

3 What worries do you have about your bladder problem?*

I worry that I will smell of urine I worry that my pads/towels will leak I worry that I will wet my clothes I worry that my pads/towels will show

4 Does your bladder problem affect your .

No a) holidays [ I b) family life [ I c) social life (like going out, seeing friends) [ I d) interestslhobbies [ I

. .

Yes [ I [ I [ I [ I

Not applicable

[ I [ I [ I [ I

To what extent do you feel that your sex life has changed because of your bladder problem?

Got better [ I

Stayed the same

[ I

Got Not

[ I 1 1 worse applicable

*NOTE: Item 3 is excluded from the recommended final version.

development of a symptom severity index and a symptom impact index for stress incontinence in women

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