The prevalence of Prostatism: A Population-Based Survey of Urinary Symptoms

0022-534 7/93/1501-0085$03.00/0 THE JOURNAL OF UROLOGY Copyright© 1993 by AMERICAN UROLOGICAL ASSOCIATION, INC.

Vol. 150, 85-89, July 1993

Printed in U.S.A.

THE PREVALENCE OF PROSTATISM: A POPULATION-BASED SURVEY OF URINARY SYMPTOMS C. G. CHUTE, L.A. PANSER, C. J. GIRMAN, J.E. OESTERLING, H. A. GUESS, S. J. JACOBSEN AND M. M. LIEBER From the Sections of Medical Information Resources and Clinical Epidemiology, Departments of Health Sciences Research and Urology, Mayo Clinic, Rochester, Minnesota, and Merck Research Laboratories, Blue Hall, Pennsylvania

ABSTRACT

To establish the age-specific prevalence of urinary symptoms among a community-based cohort of men, a randomly selected sample of men were screened and invited to participate in a longitudinal survey of urinary symptoms. The population of Olmsted County, Minnesota, as enumerated by the Rochester Epidemiology Project, formed the sampling base for this study. Men between 40 and 79 years old with no history of prostate or other urological surgery, and who also were free of conditions associated with neurogenic bladder were invited to participate. A previously validated questionnaire was completed by the subject. Urine flow measures, current medications and family histories of urinary disease were also obtained. Nonresponse corrected scores for a composite of obstructive symptoms showed moderate to severe symptomatology among 13% of the men 40 to 49 years old and 28% of those older than 70 years. Prostatism is a highly prevalent symptom complex among unselected men in the community. The specific urinary symptoms of nocturia, weak stream, restarting, urgency and sensation of incomplete emptying are strongly age-related and, therefore, may be predictive of a prostatic disease process. KEY WORDS:

prostatic hypertrophy, epidemiology, population surveillance, cross-sectional studies

Prostate symptoms are accepted by most cultures as an inevitable consequence of aging. The public health and economic impact of prostate disease in the United States is enormous, exceeding $1 billion annually for the direct costs of surgical management alone. 1• 2 Nevertheless, virtually no population-based data are available addressing the prevalence of prostatism in the United States. The frequency and severity of urological symptoms have been described in many surgical series, 3- 6 including the based population of the Rochester Epidemiology Project. 7 Fewer cohort studies are available. 8 •9 Population-based studies focusing on benign prostatic hyperplasia (BPH) have included symptoms. 10• 11 However, the former study was among volunteers for cancer screening and neither study involved North American men. In the course of establishing a cohort to study the natural history of prostate disease in a free-living, random sample of a defined population, we were able to evaluate the cross sectional prevalence of urinary symptoms at enrollment. Our report provides population-based estimates of urological symptom prevalence and severity. Furthermore, it suggests that specific urinary symptoms may be indicative of disease based on the increasing prevalence with advancing age.

5-year age strata in proportion to the underlying population demographics. Selected Olmsted County residents were excluded by preinvitation medical history screening, during subsequent telephone interviews or during the data collection interview. Excluded subjects were deceased or moribund (111), or had a history of prostate cancer or surgery (418), bladder cancer or surgery (59), other bladder disorders (20), or urethral surgery or strictures (66). Men with neurological conditions that might interfere with normal voiding, including a history of low back surgery (284), Parkinson's disease requiring medication (20), diabetic neuropathy leading to lower limb amputation (6) and other progressive neurological disorders (44), were excluded. An inability to void while in a standing position (7), any cognitive disorder that disabled a man so that he could not complete the questionnaire (58), need for renal dialysis (9) and status after anteroposterior rectum resection (4) were also exclusion criteria. Prisoners (19), residents out of the county during the study period (13), patients who do not speak English (2), and patients with billing disputes at the Mayo Clinic (116) and other administrative criteria (5) were excluded. Survey cohort members were visited in their home, office or the clinic between December 1989 and March 1991 by trained study assistants who obtained a detailed medication and family history. A pilot study validated questionnaire 14 was self-administered in the assistant's presence and checked for completeness before the interview was completed. Eligibility questions were included in the questionnaire and were used to exclude additional men after the interview. Urinary flow rates were also obtained and form the basis of a subsequent report. The complete questionnaire included 134 elements. There were 12 questions about the occurrence of urinary symptoms during the last month on a scale of O (I do not have symptom) to 6 (always) for urinary frequency (more than every 2 hours in the day), nocturia (more than once), a small or weak urinary stream, dysuria, straining, repeat urination (within 10 minutes), stopping and starting, dribbling, hesitancy, urgency, sensation of incomplete emptying and wet clothing. The average number of nocturia episodes per night during the last week was

MATERIALS AND METHODS

The population of Olmsted County, Minnesota (106,470 persons, 1990 census) was enumerated using the resources of the Rochester Epidemiology Project. This project has been continuously funded by the National Institutes of Health since 1966 as a laboratory for epidemiology and disease natural history studies. 12•13 Virtually all patient encounters to clinics, hospitals and private offices from 1986 through part of 1989 were tabulated by unique patient identifiers. A total of 14,944 men in the 40 to 79-year age group was enumerated, representing 96% of the census estimates. From this enumeration 5,135 men 40 to 79 years old on January 1, 1990 were randomly selected within Accepted for publication December 11, 1992. Supported in part by a grant from the Merck, Sharp & Dohme Research Laboratories as part of the BPH National History Study Group, and Grant AR30582 from the National Institutes of Health. 85

86

PREVALENCE OF PROSTATISM

also questioned. There were 12 additional questions on how bothersome the same symptoms had been during the last month (Oto 6 scale, from no symptom to extremely bothersome). The complete text of this questionnaire appears as an Appendix to the study of Epstein et al. 14 To estimate better symptom complexes that might indicate BPH the individual scores for obstructive symptoms (weak stream, stopping and starting, dribbling, hesitancy and incomplete emptying) were summed to yield a composite obstructive score. 15 To enhance comparability we approximated the American Urological Association (AUA) Symptom Index for BPH 16 by rescaling our data in consultation with the AUA index developers. To match the 6-point symptom frequency AUA scale, our 2 highest categories (almost always and always) were combined to map to the highest AUA category (almost always). Similarly, our 7-point bothersome scale was collapsed in the 4 highest categories to form 2 rescaled categories. These corresponded to the top 2 levels in the 5-point AUA bothersomeness scale: somewhat bothersome (3 and 4) mapped to AUA medium problem, extremely bothersome (5 and 6) mapped to AUA big problem. To evaluate potential nonresponse bias, under a separate Institutional Review Board approval protocol, we mailed a 1page symptom questionnaire to nonresponders of the study cohort. All 12 symptoms were included, with 2 response columns for frequency and bothersomeness. These scores were tabulated separately to compile the composite obstructive score. Age-strata specific correcting weights were computed by assuming the nonresponder study provided estimates for all nonresponders. These weights were then applied to the obstructive and AUA composite scores to create the nonresponse adjusted score. AUA frequency score could not be weighted directly because nocturia frequency was asked differently on the nonresponder questionnaire and, thus, the nocturia bothersome weight was applied. Of the 3,854 invited, eligible men and the 20 individuals lost before enrollment 2,119 participated in the in-home study (55% response rate). Symptom data from the nonresponder study were obtained from 638 additional men, for an overall symptom questionnaire response rate of 71 %. Roughly a quarter of the men (549) were randomly invited to an in clinic examination and repeat symptom interview within 4 months of the at home enrollment. Among these men 87% agreed to participate and 14 were found ineligible for the in clinic examination. Symptom responses were evaluated for reproducibility and consistency. Reproducibility analysis between at home and in clinic symptom data invoked the weighted kappa statistic (K) of Cohen 17 using squared weights (1, 4, 9, 16 and so forth). This technique allows partial credit for responses that are close but not identical. Symptom frequency scores yielded a weighted kappa of 0.55. Bothersomeness scores were even more consistent with a weighted kappa of 0.62. The size and demographics of the main and in clinic cohorts are shown in table 1. The in clinic validation sample is comparable to the community cohort in virtually all respects. The Olmsted County cohort is well insured and reports a high level of recent health encounters. Younger men (40 to 64 years old) tend to be better educated, employed and have higher incomes, while older men (65 to 79 years old) smoke less, are hospitalized more often and require more assistance in completing the questionnaire. Data management and tabulation were conducted in the SAS environment. 18 Kappa analysis was done in the S environment.19 RESULTS

Symptom prevalence as measured by frequency appears in table 2. The proportion of men who reported experiencing each symptom more than rarely (scale response 2 or more) is tabulated by age decade. The symptoms are divided into 2 groups:

TABLE

1. Descriptive statistics of patient characteristics

In Clinic Age

Community Cohort Age Group

No. pts. Mean age % Current smoker % Married % College graduate % Income greater than $35,000 % Employed full-time % Medically insured % Visited physician within last yr. % Hospitalized within last yr. % Completed questionnaire without assistance

TABLE 2.

Group

40-64

65-79

40-64

65-79

1,644 51 28 90 42 73

475 71 13 89 20 26

367 51 23 91 45 77

104 71 16 89 15 19

82 97 70

9 97 83

83 97 70

7 94 86

8

15

7

14

96

87

97

90

Urinary symptom frequency percentage of men with urinary symptoms occurring more than rarely Age Group (yrs.)

Total No. pts. % With symptoms showing strong age relation: Nocturia Weak stream Stopping or starting Feeling cannot wait Feel bladder not empty % With symptoms not showing age relation: Frequent urination within 2 hrs. Pain or burning Strain or push Repeat within 10 mins. Dribbling Difficulty starting Wet clothing Obstructive score:* % With score greater than 7: Correctedt Median score: Corrected+ AUA score: % With score greater than 7: Corrected§ Median score

40-49

50-59

60-69

70+

800

612

436

271

16 25 18 28 16

29 34 25 32 17

42 39 29 42 23

55 49 32 46 23

34 5 12 12 37 14 23

34 6 15 11 43 18 25

36 4 13 18 44 20 24

35 7 15 11 36 19 22

16 15 3 2

24 21 4 3

27 24 4 4

30 29 4 4

26 24 4

33 31 5

41 36 6

46 44 7

* Obstructive score is the sum of weak stream, stopping and starting, dribbling, hesitancy and incomplete emptying. t Corrected proportion is the age-stratified, weighted mean of dichtomous (0 and 1) variables with weights n/N (responders) and (N-n)/N (initial nonresponders), where N corresponds to the total number of randomly selected eligible and invited men, and n is the number of participants in the main study cohort, within age decade. :j: Corrected median scores were calculated by replicating nonresponder questionnaire data to simulate all nonresponders, and calculating the median of the combined data for respondents and initial nonresponders. This approach assumes that initial nonresponders for whom data were obtained are representative of all refusals. § AUA composite symptom frequency score not available from the nonresponder study. Corrected proportions were obtained by decreasing the study cohort proportions by the percentage reduction observed for AUA bother score, assuming a similar relationship would apply to the frequency score. Calculation of corrected AU A score median is not practical.

1) those showing an increasing prevalence with age (top) and 2) those that appear unrelated to age. Only 5 among the 12 urinary symptoms show increasing prevalence with age: nocturia, weak stream, restarting, urgency and incomplete emptying. Frequent urination and dribbling are highly prevalent symptoms, reported by more than a third of the men. However, these common symptoms show no change of prevalence with age. The per cent of men reporting significant (composite score greater than 7) symptom frequency in the obstructive and AUA score combinations also increases strongly with age.

87

PREVALENCE OF PROSTATISM

Because the 55% of invited men who responded to the main study might not represent all men in the community, we corrected the composite scores by weighting the data from our nonresponder survey to represent the 29% of invited men who were complete nonresponders. This process tended to diminish symptom prevalence; cohort members reported symptoms more often than nonresponders particularly in the younger age groups. Nevertheless, corrected AUA composite scores increase strongly with age and suggest that a quarter of the young men and nearly half of the older men report a substantial frequency of urinary symptoms in a free-living, unselected population. Responses to questions about symptom bothersomeness appear in table 3. The per cent of men at least somewhat bothered (scale 2 or more) increases with age decades for nocturia, weak stream, stopping and starting, urgency and incomplete emptying, while frequency and straining or pushing show a weaker age association. Fewer men reported bothersomeness responses of 2 or more compared to frequency responses of that magnitude, suggesting that simply having the symptom may not be considered a problem by many men. However, response scales must be compared cautiously. Nevertheless, the 3 most prevalent symptoms are also the most commonly bothersome: nocturia, urgency and weak urinary stream. Dribbling was bothersome to a quarter of all men, independent of age. Wet clothing, also not strongly related to age, was reported in about a fifth of the men. Composite bothersomeness scores (obstructive and ADA) were lower than the frequency scores, reflecting the lower TABLE

3. Percentage of men reporting urinary symptoms to be more

than a little bothersome Age Group (yrs.)

Total No. pts. % With symptoms showing strong age relation: Nocturia Weak stream Stopping or starting Feeling cannot wait Feel bladder not empty % With symptoms not showing age relation: Frequent urination within 2 hrs. Pain or burning Strain or push Repeat within 10 mins. Dribbling Difficulty starting Wet clothing Obstructive score:* % With score greater than 7: Correctedt Median: Corrected median:j: AUA score: % With score greater than 7: Corrected§ Median: Corrected median

40-49

50-59

60-69

70+

800

612

436

271

13 10 15

17 17 12 21

9

11

25 23 18 27 14

35 24 21 31 17

12

15 4 7 7 26

16 3

16

9

11 9 24

8

4

6 8

23 9 20

11

21

12 28 16 20

4

14 16

17 15 2 1

20 19 2

l

25 23 3

1

2

30 29 3 3

9

13

8

l

11 I

0

1

13 12 1 0

19 17

* Obstructive score is the sum of weak stream, stopping and starting, dribbling, hesitancy and incomplete emptying. t Corrected proportion is the age-stratified, weighted mean of dichtomous (0 and 1) variables with weights n/N (responders) and (N-n)/N (initial nonresponders), where N corresponds to the total number of randomly selected eligible and invited men, and n is the number of participants in the main study cohort, within age decade. :j: Corrected median scores were calculated by replicating nonresponder questionnaire data to simulate all nonresponders, and calculating the median of the combined data for respondents and initial nonresponders. This approach assumes that initial nonresponders for whom data were obtained are representative of all refusals. § AU A composite symptom frequency score not available from the nonresponder study. Corrected proportions were obtained by decreasing the study cohort proportions by the percentage reduction observed for AUA bother score, assuming a similar relationship could apply to the frequency score. Calculation of corrected AU A score median is not practical.

prevalence of men bothered by each symptom. Nevertheless, more than a quarter of all older men were significantly bothered by the symptoms. Correction for nonresponse did not alter the age relationships appreciably. During the construction and piloting of our questionnaire, we solicited open -ended statements from patients with BPH regarding the extent to which these symptoms interfered with their everyday activities. 9 From these statements we created 7 questions and incorporated them into our community questionnaire. Table 4 shows the proportion of men in the community whose urological symptoms interfere with their everyday activities at least some of the time (score 2 or more on a 5-point scale). More than 15% of the men older than 60 years indicated that drinking fluids before bed or traveling, and driving more than 2 hours without stopping were substantially curtailed by the symptoms. Among those men with AUA composite bothersome scores of greater than 7 these proportions more than doubled; almost half of those men avoided fluid intake before bedtime. DISCUSSION

To our knowledge our report represents the only populationbased American report of the prevalence of prostatism. A similar report recently appeared based on a small community in central Scotland. 11 The methods and questionnaire used in the Scottish study were virtually identical to our own, since we collaborated in study design and development in the context of the BPH Natural History Study Group. Table 5 compares the published Scottish prevalence rates with our data; we have revised our cutoff points to match their rates. The relative ranking of individual symptoms by prevalence are similar. However, the American men reported more symptoms overall than their Scottish counterparts. Urinary symptoms from the Baltimore Longitudinal Study of Aging were recently reported by age group. 8 Comparison with these data is problematic, since they were obtained as yes and no responses. Establishing different cutoff points for our data will influence comparability. Nevertheless, using the cutoff points selected in table 4 (scale greater than 2), our symptoms profile the Baltimore data almost completely. An apparent exception would be nocturia, which is somewhat more prevalent at each level of age in the Baltimore data. However, this difference disappears when the Baltimore data are analyzed with a nocturia definition of more than once per night similar to our own. 20 The agreement of these American cohort data suggests that the American/Scottish differences may be culturally based and not attributable to study variation or imprecision. Japanese urinary symptom data were collected in the course of a population-based prostate cancer screening program Tsukamoto et aL 10 Again, while questionnaire design and variability make comparison difficult, the inclusion of age-stratified prevalence for mild and moderate symptoms allows comment. Information from the published data permits 3 symptoms to be contrasted: nocturia (more than once per night), weak stream and hesitancy. All 3 symptoms were roughly 1.5 times more prevalent among the Japanese at each age stratum, although the general age trend relationships were similar to our own. The consistency of the elevated prevalence for all 3 symptoms, analogous to the attenuation in the Scottish data, suggests that cultural factors may be responsible for differences. This finding is nevertheless surprising in view of the low incidence of clinical BPH and transurethral resection of the prostate in Japan. 10 An important potential conclusion from these data is that many urinary symptoms may not reflect disease processes associated with aging. The prevalence of obstructive prostate disease is unquestionably related to age and, therefore, urinary symptoms attributable to bladder outflow obstruction should increase with age. The absence of an age prevalence association

88

PREVALENCE OF PROSTATISM TABLE 4.

Men reporting more than a little interference with daily activities Age Group (yrs.) 50-59

60-69

70+

7 or Less

More Than 7

7 or Less

More Than 7

800

612

436

271

1,408

710

1,701

415

10 13 9 7 6 4 5

11 14 10 8 7 3 4

15 18 15

4 7 4 3 2 1 1

26 33 27 19 21 9 12

5 8 5

11 4 5

15 20 17 13 14 5 7

3 2 2

37 43 38 29 30 14 18

43

47

56

56

34

78

39

88

Composite score

10

5. American versus Scottish prevalence of symptom occurrence % With More Than a Little Interference

Symptom

Occasional*

Oftent

United States Scotlandt United States Scotlandt Nocturia Hesitancy Straining Urgency Dribbling Stopping and starting Incomplete emptying Weak stream

38 35 28 51 49 38 36 44

AUA Bothersome Score

40-49 Total No. pts. % Total pts.: Fluids before travel Fluids before bed Driving 2 hrs. Enough sleep at night Avoid places without toilet Avoid outdoor sports Attending movies and so forth

TABLE

AUA Frequency Score

23 13 11 43 35 24 20 27

17 5

4 11 17 8 5

13

7 1 0.4 7

10 5 3 6

* Classified as present rarely or a few times. t Classified as present fairly often, usually or almost always, or always. t Compiled from the study of Garraway et al. 11

for frequent urination within 2 hours, dysuria, straining, repeat urination within 10 minutes, dribbling, difficulty starting and wet clothing suggests that these symptoms may not reflect obstructive prostatic disease. The classification of urological symptoms into obstructive and nonobstructive symptoms on the basis of their age relatedness is consistent with the clinical distinction between obstructive and irritative symptoms made in the urological literature. However, there does not appear to be general agreement among physicians as to which symptoms belong in each category, particularly nocturia and urgency. 21- 25 Thus, epidemiological studies that attempt to classify patients on the basis of symptoms may misclassify patients with respect to prostate disease if these symptoms contribute greatly to the criteria. Furthermore, health care interventions, such as transurethral resection of the prostate, which are done to address these symptoms may have disappointing results. Our study has several limitations, the most important being our decision to study urinary symptoms among men without a surgical history of prostate interventions. Thus, our current results cannot be applied to men previously treated for prostatism or who underwent urological surgery for other reasons. Our identification of 5 symptoms that may predict obstructive prostatic disease is based wholly on an inference from increasing age prevalence. However, a spectrum of pathophysiological processes might be responsible, including an age-related loss of bladder contractility26 • 27 although this speculation may be controversial. 28 We will be able to test the predictive value of symptoms for obstruction in our own cohort with time by observing which symptoms predict treatment. Therefore, these findings must be considered preliminary. We consider the marked impact that urinary symptoms have on ordinary activities of daily living to be important and quite possibly underrecognized. While the activities affected are not life-threatening, they can and do adversely affect life-style. The strong correlation with symptom frequency and the stronger correlation with bothersomeness score also serve as internal consistency checks that support the use of the composite score measures.

4

Our population-based data reflect the high prevalence of urinary symptoms among men reported in earlier cohort studies. These American data appear midway between a similarly conducted Scottish survey and Japanese screening data. Our data suggest that prostatism is common within an unselected population, and may be best characterized by nocturia, weak stream, restarting, urgency and sensation of incomplete emptying. Dr. Michael Barry reviewed our AUA score conversion algorithms. The BPH Study Research Staff, especially R. Nelson, R. Meuller, P. Van Grevenhof, C. Wilson and K. Elias, assisted with manuscript preparation. Members of the Olmsted County Urologic Survey Cohort cooperated with this study. REFERENCES

1. Graves, E. J.: Detailed Diagnoses and Procedures, National Hospital Discharge Survey, 1989. Vital and Health Statistics Series 13, No. 108. Hyattsville, Maryland: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Center for Health Statistics, 1991. 2. The Travelers Medicare Policy Manual for the State of Minnesota. Minneapolis, Minnesota: The Travelers Insurance Co., June 1991. 3. Fowler, F. J., Jr., Wennberg, J. E., Timothy, R. P., Barry, M. J., Mulley, A.G., Jr. and Hanley, D.: Symptom status and quality of life following prostatectomy. J.A.M.A., 259: 3018, 1988. 4. Bruskewitz, R. C., Larsen, E. H., Madsen, P. 0. and D!llrflinger, T.: 3-Year followup of urinary symptoms after transurethral resection of the prostate. J. Ural., 136: 613, 1986. 5. Chilton, C. P., Morgan, R. J., England, H. R., Paris, A. M. and Blandy, J. P .: A critical evaluation of the results of transurethral resection of the prostate. Brit. J. Ural., 50: 542, 1978. 6. Mebust, W. K., Holtgrewe, H. L., Cockett, A. T. K., Peters, P. C. and Writing Committee: Transurethral prostatectomy: immediate and postoperative complications. A cooperative study of participating institutions evaluating 3,885 patients. J. Ural., 141: 243, 1989. 7. Stephenson, W. P., Chute, C. G., Guess, H. A., Schwartz, S. and Lieber, M. M.: Incidence and outcome of surgery for benign prostatic hyperplasia among residents of Rochester, Minnesota: 1980-1987. A population-based study. Urology, suppl. 1, 38: 32, 1991. 8. Arrighi, H. M., Guess, H. A., Metter, E. J. and Fozard, J. L.: Symptoms and signs of prostatism as risk factors for prostatectomy. Prostate, 16: 253, 1990. 9. Epstein, R. S., Deverka, P.A., Chute, C. G., Lieber, M. M., Oesterling, J.E., Panser, L.A., Schwartz, S. W., Guess, H. A. and Patrick, D.: Urinary symptoms and quality of life questions indicative of obstructive benign prostatic hyperplasia. Results of a pilot study. Urology, suppl. 1, 38: 20, 1991. 10. Tsukamoto, T., Kumamoto, Y., Takagi, Y., Yamaguchi, Y., Yoshioka, M., Yokoyama, E., Hayashi, E., Furuya, S. and Ogura, H.: Studies on prostatism of males fifty years of age and olderanalysis on results of a second mass screening for prostatic diseases in Tanna town. Hinyokika Kiyo, 35: 1701, 1989. 11. Garraway, W. M., Collins, G. N. and Lee, R. J.: High prevalence of benign prostatic hypertrophy in the community. Lancet, 338: 469, 1991.

PREVALENCE OF PROSTATISM 12. Kurland, L. T., E1'1eback, L. R. and Nobrega, F. T.: Population studies in Rochester and Olmsted County, Minensota, 19001968. In: The Community as an Epidemiologic Laboratory. Edited by I. I. Kessler and M. L. Levin. Baltimore: The Johns Hopkins University Press, chapt. 3, pp. 47-70, 1970. 13. Kurland, L. T. and Molgaard, C. A.: The patient record in epidemiology. Sci. Amer., 245: 54, 1981. 14. Epstein, R. S., Deverka, P. A., Chute, C. G., Panser, L. A., Oesterling, J. E., Lieber, M. M., Schwartz, S. W. and Patrick, D.: Validation of a new quality of life questionnaire for benign prostatic hyperplasia. J. Clin. Epidemiol., in press. 15. Bolognese, J. A., Kozloff, R. C., Kunitz, S. C., Stoner, E., Grino, P. B., Patrick, D. L. and Taylor, A. M.: Development and validation of a symptoms and quality of life questionnaire for benign prostatic hyperplasia. In preparation. 16. Barry, M. J., Fowler, F. J., Jr., O'Leary, M. P., Bruskewitz, R. C., Holtgrewe, H. L., Mebust, W. K. and Cockett, A. T. K.: The American Urological Association Symptom Index for benign prostatic hyperplasia. J. Urol., 148: 1549, 1992. 17. Cohen, J.: Weighted kappa: nominal scale agreement with provision for scaled disagreement or partial credit. Psych. Bull., 70: 213, 1968. 18. SAS Language and Procedure Guides, Version 6.03. Cary, North Carolina: SAS Institute Inc., 1988.

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19. Becker, R. A., Chambers, J. M. and Wilks, A. R.: The New S Language. Pacific Grove, California: Wadsworth & Brooks, 1988. 20. Arrighi, M.: Personal communication. 21. Cockett, A. T. K., Aso, Y., Chatelain, C., Denis, L., Griffiths, K., Khoury, S. and Murphy, G.: Proceedings of The International Consultation on Benign Prostatic Hyperplasia (BPH). Paris: International Scientific Committee, 1991. 22. Frimodt-M0ller, P. C., Jenson, K. M-E., Iversen, P., Madsen, P. 0. and Bruskewitz, R. C.: Analysis of presenting symptoms in prostatism. J. Urol., 132: 272, 1984. 23. Claridge, M.: Analyses of obstructed micturition. Ann. Roy. Coll. Surg. Engl., 39: 30, 1966. 24. Abrams, P. H. and Feneley, R. C. L.: The significance of the symptoms associated with bladder outflow obstruction. Urol. Int., 33: 171, 1978. 25. Craigen, A. A., Hickling, J. B., Saunders, C. R. G. and Carpenter, R. G.: Natural history of prostatic obstruction. A prospective survey. J. Roy. Coll. Gen. Pract., 18: 226, 1969. 26. Mcinerney, P. D., Robinson, L. Q., Weston, P. M., Cox, R. and Stephenson, R. P.: Assessment of the poorly contractile or acontractile bladder in the older male in the absence of neuropathy. Brit. J. Urol., 65: 161, 1990. 27. O'Donnell, P. D. and Beck, C.: Urinary incontinence volume patterns in elderly inpatient men. Urology, 38: 128, 1991. 28. Benson, G. S.: Bladder dysfunction in the elderly. Amer. J. Kidney Dis., 16: 322, 1990.