We performed a cross-sectional analysis of women reporting at least weekly incontinence participating in the Reproductive Risks of Incontinence Study at Kaiser. The RRISK is a cohort of 2,109 middle-aged or older women enrolled in the Kaiser Permanente Medical Care Program of Northern California, an integrated health care delivery system serving approximately 25% to 30% of the northern California population. Previous studies have found Kaiser Permanente Medical Care Program of Northern California members to be representative of the race/ethnicity and demographic characteristics of the region served, although on average they are slightly more educated, and underrepresent the poor and the wealthy.10
To be eligible for the RRISK women had to be between 40 and 69 years old on January 1, 1999; to have been continuously enrolled in a Kaiser Permanente clinic since age 18 years and to have given birth to at least half of their children within the Kaiser Permanente system. Details on the sampling process used to construct this cohort with a race/ethnicity composition of 20% black, 20% Latina, 20% Asian and 40% white have been previously described.11
Demographic characteristics, medical histories, incontinence symptoms and quality of life impact of incontinence were assessed in the RRISK using self-reported questionnaires, and were supplemented by in-person interviews in which interviewers reviewed and clarified participant answers to questions about incontinence. A bilingual interviewer was available for women who preferred to be interviewed in Spanish but this option was selected by less than 1% of the participants. The RRISK study was approved by the institutional review boards of the University of California, San Francisco and Kaiser Permanente.
To assess incontinence symptoms participants were asked, “During the past 12 months, on average, how often have you leaked urine, even a small amount?” Women reporting at least weekly incontinence were asked to recall the number of episodes in the last 7 days occurring “with an activity like coughing, lifting, sneezing, or exercise” to distinguish stress incontinence and the number of episodes in the last 7 days occurring “with a physical sense of urgency” to distinguish urge. We classified women as having stress incontinence if more than half of incontinence episodes in the last 7 days were associated with physical activity, and as having urge incontinence if more than half of incontinence episodes were associated with a sense of urgency. Women with an equal number of stress and urge incontinence episodes were classified as having mixed incontinence. Women who reported that incontinence was not associated with physical activity or a sense of urgency were labeled as having other incontinence and were excluded from analysis. This self-report diagnostic approach has been validated by previous studies and correlated reasonably well with urodynamic findings.12
Clinical severity of incontinence was determined based on incontinence frequency and the amount of urine lost per episode using the validated Sandvik Severity Scale.13
The impact of incontinence on quality of life was measured using the Incontinence Impact Questionnaire, a validated self-administered instrument that uses 30 multiple choice questions to assess impact in 4 separate domains (physical activity, emotional health, social relationships and travel), and assigns domain specific and overall impact scores.14
Possible answers included none, some, moderate and severe, which score 1, 2, 3 and 4 points, respectively. The average score for each subscale is converted to a number between 0 and 100 by subtracting 1 and multiplying by 100/3. The total IIQ score is the sum of each subscale score and can range from 0 to 400, with higher scores indicating a greater impact on quality of life. One item from the physical domain of the IIQ (“Has urine leakage affected your physical health?”) was not included to avoid duplication with other questions elsewhere on the RRISK survey. In computing the physical activity subscale and overall IIQ scores we imputed the average of the other 5 items in the physical activity subscale for this missing item. For the purposes of our analysis we decided a priori to consider women with IIQ scores at or above the 75% percentile for the entire sample of women with weekly incontinence as having a greater quality of life impact from incontinence.
Analyses of the impact of incontinence on quality of life were confined to the 530 women who reported at least weekly incontinence and met our criteria for having stress, urge or mixed incontinence. Among these women we first compared the demographic and clinical characteristics of participants with stress, urge and mixed incontinence using chi-square tests (). We then compared the unadjusted IIQ scores as well the 4 IIQ subscale scores (travel, social, emotional and physical) among women with each type of incontinence using Wilcoxon rank sum tests ().
Demographic and clinical characteristics
IIQ scores by clinical type of incontinence
We then compared the likelihood of having a greater quality of life impact of incontinence, defined as an IIQ score in the 75th percentile or greater for all participants with weekly incontinence, in women with urge vs stress incontinence, mixed vs stress incontinence and mixed vs urge incontinence using logistic regression. We first examined unadjusted associations between clinical type of incontinence and quality of life impact, and then adjusted our estimates for those characteristics that differed significantly by type of incontinence and greater quality of life impact (ie race/ethnicity, overall health and clinical severity of incontinence). Age was also retained in the models despite the fact that it was not associated with quality of life impact in our initial univariate analysis, given that multiple other studies reported a positive association between age and quality of life impact.3,6
All analyses were performed using SAS® software version 9.1.