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The natural history of urinary incontinence in midlife women is not well described. Cross-sectional epidemiological studies have found a higher prevalence in women aged 45–55 years, an age range that coincides with the menopause transition.1 This incontinence prevalence increase in midlife has been explained, in part, by the development of urogenital atrophy associated with estrogen loss around menopause.2 Yet progression through the menopause transition does not appear to increase the risk of developing incontinence.3 Other factors are important in the development of incontinence between ages 40 and 60: age, diabetes, obesity, and a high body mass index (BMI).4
Whether the transition from pre- to postmenopause affects existing incontinence, independently of other factors, is not known. There is little information about how change in factors over time, such as transition through the menopause stages or changes in weight and body distribution, can positively or negatively affect the severity of existing incontinence. Longitudinal studies are needed to provide insight into the natural history of this condition.
We aimed to evaluate factors associated with worsening and improving of incontinence symptoms in midlife women during a period of 6 years. Specifically, we examined whether stage of the menopause transition and other factors that can vary over time, such as changes in weight and waist-to-hip ratio affected the frequency of reported incontinence symptoms. We investigated factors associated with worsening and improving incontinence between each year and over the entire 6-year period.
MATERIALS AND METHODS
This is an analysis of data from the baseline and first six annual follow-up visits (1995–2002) of women who reported incontinence during the Study of Women’s Health Across the Nation (SWAN). This study is a multicenter, multiethnic, prospective cohort study of midlife women and the menopause transition.5 Each of seven sites (Boston, MA; Chicago, IL; the Detroit area, MI; Los Angeles, CA; Newark, NJ; Pittsburgh, PA; and Oakland, CA) recruited about 450 community-dwelling midlife women, for a total cohort of 3,302 women. In SWAN, African-American, Chinese, Japanese, and Hispanic women were oversampled to allow sufficient numbers for the planned analyses by racial/ethnic group. Eligibility criteria were age 42–52 years and self-identification as one of the five racial/ethnic groups to be studied. The exclusion criteria were inability to speak English, Spanish, Japanese, or Cantonese, no menstrual period in greater than 3 months or hysterectomy and/or bilateral oophorectomy before enrollment, and current use of any reproductive hormones. The study was approved by institutional review boards at all sites, and all women gave informed consent.
In a self-administered questionnaire at each annual follow-up visit, women were asked “In the past year (or since your last study visit), have you ever leaked even a small amount of urine involuntarily?” Participants listed the frequency of their incontinence as “almost daily/daily” (daily), “several days per week” (weekly), “less than one day per week” (monthly), “less than once a month,” or “none.” Because we consider incontinence occurring less than once a month not to be clinically significant and to have a higher misclassification rate, we combined this category with “no incontinence” to create the category of no regular incontinence.
We categorized type of incontinence as “stress” if participants reported leakage with “coughing, laughing, sneezing, jogging, jumping, with physical activity or picking up an object from the floor” or as “urge” if participants reported leakage “when you have the urge to void and can’t reach the toilet fast enough.”
We defined improving and worsening incontinence in two ways. First, we evaluated change in incontinence reporting from year to year. Incontinence was considered improving if the frequency of incontinence decreased from one annual visit to the next, that is, from daily to weekly or less, from weekly to monthly or less, or from monthly to no regular incontinence. We considered incontinence worsening if the frequency of incontinence increased from one annual visit to the next, that is, from no regular incontinence (after a previous report of incontinence) to monthly or more, from monthly to weekly or more, or from weekly to daily. We defined no change in incontinence as the same reported level of frequency from one annual visit to the next. Second, we evaluated change over the full 6 years of follow-up in the following manner. From one year to the next, a change from less frequent incontinence to more frequent incontinence was assigned a numerical value of +1, a change from more frequent incontinence to less frequent incontinence a value of –1, and no change in frequency, a value of 0. We summed these values of change over the 6 years. Women whose scores were less than 0 were considered to have improved, those whose scores were greater than 0 were considered to have worsened, and those with a score of 0 were considered to have no change. A no-change score could represent either consistent reporting of the same frequency of incontinence from year to year or variable reporting of frequency from year to year that summed to 0. We subdivided this group into “no change with low reporting variance” and “no change with high reporting variance,” respectively. Similarly, we determined the proportion of women who only worsened (that is, never reported improvement from year to year) and only improved (that is, never reported worsening from year to year) over the 6 years.
Our main independent variables in this analysis were menopause transition category and hormone use determined in the year before the reported change in incontinence frequency. We classified menopause status from questions assessing menstrual bleeding patterns on annual follow-up interview questionnaires as follows: Premenopause was defined as less than 3 months of amenorrhea and no menstrual irregularities in the previous year; Early Perimenopause was less than 3 months of amenorrhea and some menstrual irregularities in previous year; Late Perimenopause was 3 to 11 months of amenorrhea; Postmenopause was 12 consecutive months of amenorrhea with no apparent medical cause. The SWAN study defined surgical menopause as hysterectomy (with or without oophorectomy) or bilateral oophorectomy.
Women who started using hormones in pre-, early peri-, and late perimenopause were considered to be hormone users with an unclassifiable menopausal status. We divided post- and surgical menopausal women into those using and those not using hormone therapy when numbers in each category were sufficient for analysis. To account for change in menopausal status between years, we classified women as having transitioned from one menopausal stage to another, started using hormones, stopped using hormones, or as having no change in their status. Finally, from the baseline and year 6 menopause status, we created categorical variables to reflect the change in status over the 6 years: from pre-/early perimenopause to pre-/early perimenopause (ie, no change in status), to late perimenopause, to postmenopause, to surgical menopause, and to unclassifiable menopause status.
Weight and waist-to-hip ratio changes were also main variables of interest. Certified staff used calibrated scales and a stadiometer to measure height, weight, and waist and hip circumferences. We calculated baseline BMI as weight in kilograms/(height in meters)2 and waist-to-hip ratio as waist circumference in centimeters/hip circumferences in centimeters. We defined weight gain from year to year as an increase in weight per pound; gain in waist-to-hip ratio was an increase by 0.1 units.
Given that a woman’s initial reported frequency of incontinence is likely to impact whether her incontinence improves or worsens, we controlled for this effect by treating frequency of incontinence at first report as an independent variable. We estimated socioeconomic status by level of difficulty paying for basics. The SWAN study obtained self-reported medical history and medication use, including hormone use by interview. The study used an adaptation of the Medical Outcomes Study 36-Item Short-Form Health Survey (SF-36),6 the Center for Epidemiological Studies-Depression (CES-D) scale,7 and the Medical Outcomes Study Social Support Survey8 and Life Stressors and Social Resources Inventory (LISRES).9,10 Anxiety symptoms were measured by a summed score of days in the past 2 weeks in which certain symptoms were experienced (irritability, feeling tense or nervous, pounding or racing heart, feeling fear for no reason); anxious was defined by a score of 4 or more.11 For these time-dependent covariates, we evaluated whether new onset medical conditions and change in scales and/or events from year to year were associated with change in incontinence frequency.
For each time-dependent variable, we also created summary variables describing the patterns of change. We categorized weight gain and loss as a change of greater than 5% from baseline weight at year 6. For waist-to-hip ratio, gain was defined as an increase of greater than 7.5% or loss more than 2.5% from baseline waist-to-hip ratio. For variables whose change could be bidirectional, we accounted for variability in the change over time (eg, weight cycling) by entering the standard deviation of change over the 6 years into our models.
Dropouts included continent women who were deceased, discontinued the study, or could not be contacted for two or more consecutive visits. Incontinent women were retained in the analysis as long as they contributed data. When a woman was missing data on frequency and type of incontinence from one or two visits, we imputed values as follows. If one missing value occurred at baseline, we imputed the value from the subsequent visit. If the missing value occurred at year 6, we imputed the value at the previous visit. If the missing values were between concordant values, we imputed that concordant value. If one missing value occurred between two discordant values, we randomly assigned it the value of the previous or subsequent visit. If two missing values occurred in sequence between two discordant ones, we randomly assigned the missing values the previous and subsequent observed values. We did not impute for three or more missing data points. Overall, we imputed incontinence frequency for 808 women at 1,150 visits (5.0% of all visits) and incontinence type for 447 women at 572 visits (2.5% of all visits). When weight or waist-to-hip ratio were missing for one or two visits, the values were imputed as the mean between the two known values (weight: 263 women at 394 visits, 1.7% of all visits; waist-to-hip ratio: 257 women at 374 visits, 1.6% of all visits).
We checked each continuous covariate for normality by conducting either a Q-Q plot or a Lilliefors test, an adaptation of the Kolmogorov-Smirnov test. Distributions of incontinence and other important variables for women who remained in (analysis cohort) and who dropped out of (dropout cohort) our study were then compared using the t test or Mann-Whitney U statistic for continuous data and χ2 or proportional tests for categorical data. After selecting candidate variables based on the literature and a priori hypotheses, we used multivariable analysis to examine which factors were associated with improving and worsening incontinence. To build our models, we used backward and forward stepwise processes entering variables based on our hypotheses or based on associations with the incontinence outcome at P≤.10. In our data analysis, we used SAS 9.1 (SAS Institute Inc., Cary, NC).
We used generalized estimating equations, a methodology for dealing with repeated measures in longitudinal data, to evaluate factors associated with improving or worsening incontinence from year to year.12 We developed models to compare the following: improving with worsening/no change in incontinence as the reference, worsening incontinence with improving/no change in incontinence as the reference. For women who reported only stress or urge incontinence at two or more visits, we developed models for improving and worsening stress or urge incontinence between those visits. Because our main objective was to evaluate the effect of menopausal status and change in status on incontinence independent of age, we forced these factors into our final models. After checking for collinearity and model stability, including with and without imputation, we chose our final models with imputation based on the lowest QIC (quasi-likelihood under independence model criterion) and the related QICu statistic, which indicate the best fit for generalized estimating equations models.13,14
We also used regression modeling to evaluate factors associated with change in frequency of incontinence over the entire 6-year period using the 6-year summary outcomes and independent variables described above. We assumed that low variance in reporting no change in incontinence would be a stable reference group. We compared odds of high variance in reporting no change in incontinence, odds of improving with low variance no change/worsening incontinence, and odds of worsening with low variance no change/improving incontinence.
Table 1 displays the baseline characteristics of the women in SWAN’s inception cohort, of those incontinent women in our analysis (analysis cohort), and of those women who did not report incontinence before being lost to follow-up by the sixth annual visit (drop-out cohort). Women who remained in the study and never reported incontinence are not included in our analysis and are therefore not shown in this table. Women in our analysis cohort compared with the dropout cohort were less likely to be Hispanic, had less difficulty paying for basics, were more likely to have gone to college, had higher parity, had a higher BMI, and were more likely to report anxiety symptoms at baseline.
Of the 2,415 women who reported monthly or more incontinence during the 6 years, 2,230 (92.3%) contributed information to our analysis. About 30.6% of women reported only stress incontinence, and 9.7% of women reported only urge incontinence symptoms over all 6 years. The remainder reported either or both symptoms from year to year. Overall, 14.7% of incontinent women reported worsening, 32.4% reported improvement, and 52.9% reported no change in the frequency of incontinence symptoms.
Figure 1 provides the percentages of women who had remained pre- or early perimenopausal and who transitioned to early peri-, late peri-, post-, surgical, or unclassifiable menopausal status by year 6. It also displays the percentages of women who gained, lost, or maintained weight and waist/hip ratios by year 6.
Although few stages of the menopausal transition were statistically significantly associated with increased odds of improving incontinence, most of the estimated odds ratios for improving incontinence in early and late peri- and postmenopause were greater than 1.00 (Table 2). For women reporting any or stress incontinence, early perimenopausal status was associated with improvement in incontinence symptoms. Consistent with this, although not statistically significant, the corresponding estimated odds ratio for urge incontinence also indicated improvement for this status. Advancing in menopausal status was significantly associated with increased odds of improvement for any incontinence, but not for stress and urge incontinence. However, the estimated odds ratios were identical for each of the three categories of incontinence (any, stress, urge), suggesting a consistent effect for stress and urge incontinence. The lack of statistical significance for the association between menopausal status and specific incontinence type likely reflects an insufficient sample size to detect such a departure from the null hypothesis. Hormone use, including either starting or stopping hormone therapy, in the previous year was not associated with improving incontinence in the subsequent year for any and stress incontinence. Meanwhile, starting hormones was associated with improvement in urge incontinence.
We found several factors that were associated with increased odds of reporting improvement in incontinence symptoms. When a woman’s first report of incontinence frequency was daily or weekly, she was subsequently more likely to improve compared with a woman whose first report of incontinence frequency was monthly. Women with no history of smoking were more likely to report improvement in any incontinence. On the other hand, weight gain and increased anxiety symptoms were associated with lower odds of improvement.
Although few stages of the menopausal transition were statistically significantly associated with lower odds of worsening incontinence, the estimated odds ratios for early and late peri- and postmenopause were all less than 1.00 (Table 3). Compared with premenopausal women not using hormones, postmenopausal women not using hormones were less likely to report worsening incontinence. The odds ratios for any and urge incontinence were significantly reduced for postmenopausal women not using hormones, and the estimate for stress incontinence was consistent with these odds ratios. Similarly, the use of hormones in the pre-, early, or late perimenopause was also associated with a consistent pattern of estimated odds ratios less than 1.00.
Weight gain was associated with increased odds of worsening any, stress, and urge incontinence, while an increase in waist-to-hip ratio increased odds of worsening any and stress incontinence. A college degree or higher was associated with lower odds of worsening stress incontinence, while stressful life events increased odds of worsening any and stress incontinence. Hispanic ethnicity was associated with increased odds of worsening stress and urge incontinence. African-American race and anxiety symptoms were significantly associated with higher odds of worsening of any and stress incontinence. Here again, the estimated odds ratios for the association between African-American race and anxiety symptoms and worsening urge incontinence were in a consistent direction with those for any and stress incontinence but were not statistically significant.
For women who worsened or improved over the 6 years, 329 (40.0%) worsened without ever reporting improvement, and 218 (29.4%) improved without ever reporting worsening. Of the 470 women who had no total change in their incontinence status over the 6 years, 54.7% reported mostly the same level of incontinence year to year (low reporting variance), while 45.3% reported different levels of frequency from year to year (high reporting variance). Women with a high variance in reporting the frequency of their incontinence were more likely to have a high baseline BMI (odds ratio [OR] 1.02; 95% confidence interval [CI] 1.00–1.04), have more weight cycling (OR 1.07; 95% CI 1.00–1.16), and report anxiety symptoms at baseline (OR 1.57; 95% CI 1.11–2.23).
In our models assessing factors associated with improving and worsening incontinence over the entire 6-year period, we found no association with change in menopausal status. In these models, African Americans (OR 1.64; 95% CI 1.24–2.19) had higher odds of worsening incontinence compared with Caucasians. Women who lost weight were less likely to report worsening incontinence (OR 0.63; 95% CI 0.41–0.96), while women who weight cycled (OR 1.07; 95% CI 1.01–1.14) were more likely to report worsening incontinence.
We found few statistically significant associations between natural menopause transition stage and change in the frequency of incontinence symptoms. Being in early perimenopause was associated with improvement in any and stress incontinence, and being in postmenopause reduced odds of worsening for any and urge incontinence. Taken as a whole, the direction and internal consistency of our results suggest a weak positive effect of the menopause transition on any, stress, and urge incontinence. Early and late peri- and early postmenopause were associated with modestly increased odds of improvement and reduced odds of worsening incontinence compared to premenopause. Although our statistical power was insufficient to confirm this observed modest positive effect, our results do not support the belief that worsening incontinence is attributable to the menopausal transition.
Women in pre-, early, or late perimenopause who started using hormones in the previous year were less likely to worsen in any incontinence symptoms with the same trend seen in stress and urge types. Previous longitudinal cohort studies15 and randomized, controlled trials16,17 assessing the effects of hormone therapy on incontinence in postmenopausal women have found that hormone use worsens both stress and urge incontinence in postmenopausal women. The effects of exogenous estrogen in pre- and perimenopausal women may be different from those in postmenopausal women due different distributions of α and β estrogen receptors and, thus, actions of estrogen, in the urogenital tract before and after the final menstrual period.18 However, our finding of a negative association between hormone use in pre-, early, and late perimenopause and worsening incontinence is weak. We found no definitive pattern suggesting that hormone use in these stages was associated with improved incontinence. Specifically, using hormones before the final menstrual period did not appear to decrease odds of worsening incontinence, and starting exogenous hormones at any stage was only associated with improvement in urge incontinence symptoms.
The majority of incontinent women in midlife experience no change or improvement in their incontinence symptoms. We found few factors other than early perimenopause to be significantly associated with improving incontinence only. Having never smoked appeared to increase odds of improving any incontinence. Good social support was associated with increased odds of improving and having a college education with lower odds of worsening stress incontinence. Women who have never smoked are less likely to have a chronic lung disease, which has been associated with incontinence in some populations.19 Although we could not account for the effect of treatment on incontinence in our models, women with better social support and education are more likely to seek treatment; this may account for the positive effect on stress incontinence.
Overall only about 15% of incontinent midlife women reported worsening. Our longitudinal analysis showed that weight gain from year to year and over 6 years was associated with both a reduction in odds of improvement and an increase in odds of worsening incontinence symptoms. An increase in waist-to-hip ratio worsened any and stress incontinence. In cross-sectional studies, high BMI and waist circumference are factors associated with prevalent incontinence4,19; weight gain and increases in waist-to-hip ratio have cogent theoretical explanations for worsening existing incontinence. For example, being overweight, especially with central adiposity increases intra-abdominal pressure and, thus, pressure on the bladder and pelvic organ support structures.
African-American women, Hispanic women, and women reporting stressful life events were more likely to report worsening incontinence symptoms. African-American women appear to have a higher odds of developing stress incontinence in midlife for unclear reasons.4 Also unclear is the mechanism for a direct effect of stressful life events. Although psychological stress could increase muscular tension, neurotransmitters, or hormones that impact bladder and urethral function, stress may also increase behaviors that increase incontinence or increase the reporting of incontinence symptoms.
We found a few factors associated with both worsening and improving incontinence. Women whose first report of incontinence was daily or weekly were less likely to worsen and more likely to improve. This finding is, in part, due to constraints of our categorical incontinence frequency variables, that is, women who reported daily incontinence could not worsen by the categories of incontinence frequency used in SWAN. However, it is also possible that women with more severe or frequent incontinence are more likely to seek treatment and/or experiment with behavioral strategies such as decreasing fluid intake and increasing voiding frequency to reduce incontinence symptoms. Although women whose anxiety scores increased from year to year were more likely to worsen and less likely to improve in their incontinence, women who developed anxiety over all 6 years were more likely to have a higher variability in their reporting of incontinence over the years of our study, that is, they were more likely to report both worsening and improving over time. Reporting of incontinence symptom frequency may increase or decrease with changes in parallel with anxiety symptoms.
Our study had a number of limitations. The SWAN cohort was not assembled specifically to evaluate incontinence. Loss to follow-up or missing data can introduce bias and is always an important problem in longitudinal studies. While over 90% of the incontinent women in this study contributed information toward our analysis, the differences between those in our analysis cohort and those who dropped out limit the generalizability of our results. We attempted to evaluate both short-term (year to year changes) and long-term (change over all 6 years) worsening and improving in incontinence. The short-term changes may represent reporting variance rather than true changes in incontinence frequency, and we have attempted to evaluate and control for this by including factors that could affect incontinence reporting in our models (such as social support) and by assessing the proportions of women whose incontinence reporting varied more from year to year. Our models for long-term change identified few factors associated with either worsening or improving incontinence. Whether our method for summing change over time explains these limited results or whether fewer factors predict longer-term change cannot be assessed. The SWAN study’s definition of surgical menopause includes women who had a hysterectomy without reference to removal of ovaries. We do not have data between baseline and year 6 to evaluate longitudinally how treatment of incontinence contributed to improvement of incontinence symptoms in our cohort. Finally, because the questions eliciting the frequency of incontinence did not quantify leakage by type, we had limited power to assess change in the frequency of each incontinence type over these 6 years.
Our study also had a number of important strengths. Six years of longitudinal data on incontinence in almost 2,500 midlife women is unique, and SWAN has provided an opportunity to evaluate incontinence in a racially/ethnically diverse, community-based cohort of women over time. Second, the same incontinence questions were asked on an annual basis. Although self-report reflects the symptoms rather than the condition of stress and urge incontinence, the experience of incontinence is of more direct clinical and public health importance than the presence or absence of urodynamic abnormalities. The sensitivity and specificity of self-reported incontinence by type is estimated at 75–86% and 60–79% in validated questionnaires.20,21 Although the incontinence questions in SWAN were not from validated questionnaires, they are similar to such currently validated questions and those that have been used widely in other epidemiological studies.19,22
Many women and clinicians have believed urinary incontinence to be a symptom attributable to the menopausal transition, but our results suggest that the transition from pre- or early peri- to postmenopause has either no effect or possibly a weak positive effect on changes in the frequency of incontinence symptoms in midlife women. Instead, other modifiable factors such as weight gain and changes in weight distribution may account for any worsening in incontinence symptoms noted during this life stage.
1. Hannestad YS, Rortveit G, Sandvik H, Hunskaar S. A community-based epidemiological survey of female urinary incontinence: the Norwegian EPINCONT study. Epidemiology of Incontinence in the County of Nord-Trondelag. J Clin Epidemiol 2000;53:1150–7.
2. Bachmann G. Urogenital ageing: an old problem newly recognized. Maturitas 1995;22 suppl:S1–5.
3. Sherburn M, Guthrie JR, Dudley EC, O’Connell HE, Dennerstein L. Is incontinence associated with menopause? Obstet Gynecol 2001;98:628–33.
4. Waetjen LE, Liao S, Johnson WO, Sampselle CM, Sternfield B, Harlow SD, et al. Factors associated with prevalent and incident urinary incontinence in a cohort of midlife women: a longitudinal analysis of data: study of women’s health across the nation. Am J Epidemiol 2007;165:309–18.
5. Sowers M, Crawford S, Sternfeld B, et al. SWAN: a multicenter, multiethnic, community-based cohort study of women and the menopausal transition. In: Lobo, RA, Kelsey JL, Marcus R, editors. Menopause: biology and pathobiology. San Diego (CA): Academic Press; 2000:175–88.
6. McHorney CA, Ware Jr, JE Raczek AE. The MOS 36-Item Short-Form Health Survey (SF-36): II. Psychometric and clinical tests of validity in measuring physical and mental health constructs. Med Care 1993;31:247–63.
7. Radloff L. The CES-D Scale: a self-report depression scale for research in the general population. Appl Psychol Meas 1977;1:385–401.
8. Sherbourne CD, Stewart AL. The MOS social support survey. Soc Sci Med 1991;32:705–14.
9. Moos RH, Fenn CB, Billings AG, Moos BS. Assessing life stressors and social resources: applications to alcoholic patients. J Subst Abuse 1988;1:135–52.
10. Dohrenwend BS, Dohrenwend BP. Life stress and illness: formulation of the issues. New York (NY): Prodist; 1981.
11. Spielberger C, Gorsuch R, Lushene R. STAI manual for the State-Trait Anxiety Inventory. Palo Alto (CA): Consulting Psychologists Press; 1970.
12. Diggle P, Heagerty P, Liang K, Zeger S. Analysis of longitudinal data. 2nd ed. New York (NY):Oxford University Press; 2002.
13. Hardin JW, Hilbe JM. Generalized estimating equations. Boca Raton (FL): Chapman & Hall; 2003.
14. Pan W. Akaike’s information criterion in generalized estimating equations. Biometrics 2001;57:120–5.
15. Grodstein F, Lifford K, Resnick NM, Curhan GC. Postmenopausal hormone therapy and risk of developing urinary incontinence. Obstet Gynecol 2004;103:254–60.
16. Grady D, Brown JS, Vittinghoff E, Applegate W, Varner E, Snyder T. Postmenopausal hormones and incontinence: the Heart and Estrogen/Progestin Replacement Study. Obstet Gynecol 2001;97:116–20.
17. Hendrix SL, Cochrane BB, Nygaard IE, Handa VL, Barnabei VM, Iglesia C, et al. Effects of estrogen with and without progestin on urinary incontinence. JAMA 2005;293:935–48.
18. Gebhart JB, Rickard DJ, Barrett TJ, Lesnick TG, Webb MJ, Podratz KC, et al. Expression of estrogen receptor isoforms alpha and beta messenger RNA in vaginal tissue of premenopausal and postmenopausal women. Am J Obstet Gynecol 2001;185:1325–30, discussion 1330–1.
19. Jackson RA, Vittinghoff E, Kanaya AM, Miles TP, Resnick HE, Kritchevsky SB, et al. Urinary incontinence in elderly women: findings from the Health, Aging, and Body Composition Study. Obstet Gynecol 2004;104:301–7.
20. Bradley CS, Rovner ES, Morgan MA, Berlin M, Novi JM, Shea JA, et al. A new questionnaire for urinary incontinence diagnosis in women: development and testing. Am J Obstet Gynecol 2005;192:66–73.
21. Brown JS, Bradley CS, Subak LL, Richter HE, Kraus SR, Brubaker L, et al. The sensitivity and specificity of a simple test to distinguish between urge and stress urinary incontinence. Ann Intern Med 2006;144:715–23.
22. Brown JS, Grady D, Ouslander JG, Herzog AR, Varner RE, Posner SF. Prevalence of urinary incontinence and associated risk factors in postmenopausal women. Heart & Estrogen/Progestin Replacement Study (HERS) Research Group. Obstet Gynecol 1999;94:66–70.