the overactive bladder syndrome ( oab ) represents a group of prevalent 
 micturition symptoms that are known to have a negative impact on quality of life 
 [ 13 ] . population - based studies on women report a prevalence of oab 
 that varies between 9.7% and 35.7% , with a substantial rise in prevalence with 
 increasing age [ 4 , 5 ] . approximately 50% of women with oab reported 
 experiencing symptoms that were bothersome in their daily life . the oab syndrome is 
 internationally defined as : urinary urgency , usually accompanied by frequency and 
 nocturia with or without urgency urinary incontinence , in the absence of urinary 
 tract infection or other obvious pathology . however , in research on the outcome of treatment 
 modalities for oab , the primary outcome in the majority of studies is the reduction 
 in daily micturition and/or urinary incontinence episodes . [ apparently there is a discrepancy between the importance of the urgency symptom in 
 making a diagnosis of oab , and in the evaluation of oab treatment . this raises the 
 question whether the severity of the urgency symptom is quantitatively associated 
 with objective parameters as measured with a bladder diary and filling 
 cystometry . the aim of our study is to assess the association between bothersome oab 
 symptoms and objective bladder diary and filling cystometry measures . a retrospective cohort study was performed with a database containing 6,876 
 questionnaires that were completed by women who were referred to our 
 urogynecological center between 2003 and 2009 . from this database our final study 
 population comprised 3,280 women with 48-h bladder diaries and 2,153 women with 
 available information on filling cystometries . this study was reviewed by our 
 medical research ethics committee ( mrec ) , which concluded that no medical research 
 involving human subjects act ( wmo ) approval was needed , since the study neither 
 implied that the women would receive a particular treatment , nor impacted on the 
 behavior of the women . as part of the routine work - up , all women filled out the validated dutch 
 version of the urinary distress inventory ( udi ) . each item measures if 
 a micturition symptom is present and to what extent the patient is bothered by 
 this symptom . bother is measured on a four - point likert scale ranging from not at 
 all to greatly bothered . for the purpose of this study we selected four lower 
 urinary tract symptoms ( luts ) from the udi that are in concordance with ics 
 definitions . luts were assessed with the following questions : on frequency 
  do you experience frequent urination ?  , on 
 urgency  do you experience a strong feeling of urgency to 
 empty your bladder ?  , on nocturia  do you 
 experience frequent urination at night ?  , on urgency incontinence 
  do you experience urine leakage related to a feeling of 
 urgency ?  . group 1 consisted of women without the symptom , or those with the symptom but 
 without any bother . group 2 consisted of women who were slightly , moderately or 
 greatly bothered by one of the symptoms . women were asked to complete a 24-h bladder diary during a minimum of 2  days , 
 prior to their consultation at our center . from these dairies , time and volume 
 ( measured with a measuring cup ) of voiding episodes , as well as time and amount of 
 fluid intake were noted 
 along with complaints of pain , urgency , straining to void , and bandage changes . 
 from the bladder diaries we extracted the following information : daytime urinary 
 frequency , nocturnal frequency , minimum voided volume , maximum voided volume , mean 
 voided volume , and incontinence episodes . filling cystometry ( medtronic duet ; medtronic , minneapolis , mn , usa ) was 
 performed at an infusion rate of 50  ml / min . we did not collect all information about drug 
 use , which might influence bladder function . in case of performing cystometry , all 
 women stopped using anticholinergic drugs for at least one week prior to the 
 investigation . finally , we collected data on age and parity . the frequencies of reported oab symptoms , mean age , and parity of women were 
 assessed . a student s t test was used to 
 compare mean bladder diary and filling cystometry parameters between groups . the 
 chance of finding statistically , but not clinically significant differences 
 increases with a large study sample . in order to assess the strength of the 
 relationship , effect sizes ( cohen s d ) were calculated for all statistically 
 significant differences ( p  <  0.05 ) . an 
 effect size between 0.2 and 0.4 was considered small , between 0.5 and 0.7 medium , 
 and 0.8 as large . those oab 
 symptoms that proved to be significantly associated with bladder diary and filling 
 cystometry parameters at a p value < 0.10 , 
 were entered into a linear multiple regression analysis , with the bladder diary 
 and cystometry items as dependent variables . a subanalysis was performed on the data of women who 
 also underwent a cystometry . a retrospective cohort study was performed with a database containing 6,876 
 questionnaires that were completed by women who were referred to our 
 urogynecological center between 2003 and 2009 . from this database our final study 
 population comprised 3,280 women with 48-h bladder diaries and 2,153 women with 
 available information on filling cystometries . this study was reviewed by our 
 medical research ethics committee ( mrec ) , which concluded that no medical research 
 involving human subjects act ( wmo ) approval was needed , since the study neither 
 implied that the women would receive a particular treatment , nor impacted on the 
 behavior of the women . as part of the routine work - up , all women filled out the validated dutch 
 version of the urinary distress inventory ( udi ) . each item measures if 
 a micturition symptom is present and to what extent the patient is bothered by 
 this symptom . bother is measured on a four - point likert scale ranging from not at 
 all to greatly bothered . for the purpose of this study we selected four lower 
 urinary tract symptoms ( luts ) from the udi that are in concordance with ics 
 definitions . luts were assessed with the following questions : on frequency 
  do you experience frequent urination ?  , on 
 urgency  do you experience a strong feeling of urgency to 
 empty your bladder ?  , on nocturia  do you 
 experience frequent urination at night ?  , on urgency incontinence 
  do you experience urine leakage related to a feeling of 
 urgency ?  . group 1 consisted of women without the symptom , or those with the symptom but 
 without any bother . group 2 consisted of women who were slightly , moderately or 
 greatly bothered by one of the symptoms . women were asked to complete a 24-h bladder diary during a minimum of 2  days , 
 prior to their consultation at our center . from these dairies , time and volume 
 ( measured with a measuring cup ) of voiding episodes , as well as time and amount of 
 fluid intake the frequency and amount of incontinence were noted 
 along with complaints of pain , urgency , straining to void , and bandage changes . 
 from the bladder diaries we extracted the following information : daytime urinary 
 frequency , nocturnal frequency , minimum voided volume , maximum voided volume , filling cystometry ( medtronic duet ; medtronic , minneapolis , mn , usa ) was 
 performed at an infusion rate of 50  ml / min . we did not collect all information about drug 
 use , which might influence bladder function . in case of performing cystometry , all 
 women stopped using anticholinergic drugs for at least one week prior to the 
 investigation . the frequencies of reported oab symptoms , mean age , and parity of women were 
 assessed . a student s t test was used to 
 compare mean bladder diary and filling cystometry parameters between groups . the 
 chance of finding statistically , but not clinically significant differences 
 increases with a large study sample . in order to assess the strength of the 
 relationship , effect sizes ( cohen s d ) were calculated for all statistically 
 significant differences ( p  <  0.05 ) . an 
 effect size between 0.2 and 0.4 was considered small , between 0.5 and 0.7 medium , 
 and 0.8 as large . those oab 
 symptoms that proved to be significantly associated with bladder diary and filling 
 cystometry parameters at a p value < 0.10 , 
 were entered into a linear multiple regression analysis , with the bladder diary 
 and cystometry items as dependent variables . a subanalysis was performed on the data of women who 
 also underwent a cystometry . ninety - five bladder diaries were excluded , because the women did not 
 report any luts . the mean age of the studied population was 54.8  years ( 14.7  years ) 
 and 85.2% were parous women . the prevalence of reported oab symptoms in our study 
 population is shown in table  1 . the vast 
 majority of women ( 92% ) experienced more than one bothersome lower urinary tract 
 symptom . the combination of bothersome urgency , frequency , and nocturia was reported 
 by 34.4% of women , and 26.2% of women additionally experienced urgency 
 incontinence.table 1prevalence of bothersome overactive bladder ( oab ) 
 symptomsoab symptomwomen , n ( % ) frequency2,349 ( 73.8)urgency2,153 ( 67.6)nocturia1,536 ( 48.2)urge incontinence1,929 ( 60.6)the data shown were calculated using the udi 
 questionnaires prevalence of bothersome overactive bladder ( oab ) 
 symptoms the data shown were calculated using the udi 
 questionnaires the results of the univariate analysis ( unpaired samples 
 t test ) are shown in tables  2 
 and 
 3 . the presence of bothersome oab 
 symptoms showed a statistically significant ( p  <  0.05 ) association with almost all bladder diary and filling 
 cystometry parameters . if we consider an effect size 0.8 to be clinically relevant , 
 the frequency symptom is best associated with daytime frequency , the nocturia 
 symptom with nocturnal frequency , and the urgency incontinence symptom with 
 incontinence episodes . bladder diary and filling cystometry recorded filling volumes 
 were significantly smaller in women with bothersome oab symptoms than in women 
 without bothersome oab symptoms . the strongest association regarding volume 
 measurements and oab symptoms was found between frequency of voiding and the mean 
 voided volume . although statistically significant associations were found for the 
 urgency symptom , the effect sizes were small , which may indicate little clinical 
 relevance . subanalysis of bladder diaries that were completed by women without 
 anticholinergic therapy did not alter any of the results ( data available on 
 request).table 2mean outcomes with regard to bladder diary parameters for each oab 
 symptomoab symptombladder diary measuresgroup 1 , mean ( standard deviation)group 2 , mean ( standard deviation)cohen s dfrequencydaytime frequency episodes7.2 ( 2.2)9.4 ( 3.1)0.82*nocturnal frequency episodes0.8 ( 0.9)1.4 ( 1.2)0.59*incontinence episodes2.3 ( 3.0)3.6 ( 4.0)0.37*vol minimum114 ( 78)85 ( 58)0.42*vol mean275 ( 108)215 ( 88)0.61*vol maximum507 ( 205)432 ( 187)0.39*urgencydaytime frequency episodes7.9 ( 2.5)9.2 ( 3.2)0.45*nocturnal frequency episodes1 ( 1.0)1.4 ( 1.2)0.32*incontinence episodes2.8 ( 3.3)3.5 ( 4.0)0.22*vol minimum101 ( 70)90 ( 63)0.17*vol mean253 ( 105)222 ( 92)0.32*vol maximum486 ( 205)436 ( 188)0.26*nocturiadaytime frequency episodes8.1 ( 2.7)9.5 ( 3.2)0.45*nocturnal frequency episodes0.7 ( 0.8)1.9 ( 1.3)1.05*incontinence episodes2.8 ( 3.2)3.8 ( 4.3)0.28*vol minimum103 ( 72)83 ( 57)0.43*vol mean256 ( 103)205 ( 84)0.55*vol maximum492 ( 200)409 ( 180)0.44*urge incontinencedaytime frequency episodes8.6 ( 3.1)8.8 ( 3.0)0.07**nocturnal frequency episodes1.2 ( 1.2)1.3 ( 1.2)0.08*incontinence episodes1.4 ( 2.6)4.5 ( 3.9)0.92*vol minimum96 ( 71)92 ( 62)0.06**vol mean241 ( 103)227 ( 94)0.14*vol maximum462 ( 199)447 ( 192)0.07*group 1 : women without symptoms , or symptoms that were not at all 
 bothersomegroup 2 : women with bothersome symptomsvol : volume in milliliters*p  <  0.05**p    0.05 and 
 < 0.10table 3mean outcomes on filling cystometry parameters for each oab 
 symptomoab symptomfilling cystometry measuresgroup 1 , mean ( standard deviation)group 2 , mean ( standard deviation)cohen s d*frequencyvol first desire to void235 ( 133)196 ( 120)0.31vol normal desire to void332 ( 144)275 ( 141)0.40vol strong desire to void495 ( 171)412 ( 167)0.49vol maximum cystometric capacity555 ( 171)473 ( 168)0.48urgencyvol first desire to void229 ( 135)195 ( 118)0.27vol normal desire to void320 ( 148)275 ( 140)0.31vol strong desire to void467 ( 176)417 ( 168)0.29vol maximum cystometric capacity527 ( 176)479 ( 168)0.28nocturiavol first desire to void221 ( 127)191 ( 120)0.24vol normal desire to void309 ( 148)271 ( 137)0.24vol strong desire to void469 ( 173)398 ( 163)0.42vol maximum cystometric capacity534 ( 172)455 ( 164)0.47urge incontinencevol first desire to void213 ( 127)202 ( 124)0.09vol normal desire to void306 ( 144)281 ( 143)0.17vol strong desire to void457 ( 172)421 ( 170)0.21vol maximum cystometric capacity520 ( 171)480 ( 171)0.23group 1 : women without symptom , or with symptoms that were not at 
 all bothersomegroup 2 : women with bothersome symptomsvol : volume in milliliters*p  <  0.05 mean outcomes with regard to bladder diary parameters for each oab 
 symptom group 1 : women without symptoms , or symptoms that were not at all 
 bothersome group 2 : women with bothersome symptoms vol : volume in milliliters mean outcomes on filling cystometry parameters for each oab 
 symptom group 1 : women without symptom , or with symptoms that were not at 
 all bothersome group 2 : women with bothersome symptoms vol : volume in milliliters the results of the multiple regression analysis are listed in table  4 . after multivariate analysis for other oab symptoms , 
 the factor that was most strongly associated with bladder diary daytime frequency 
 was the frequency symptom . the standardized  coefficients indicate that this effect 
 was two to five times higher than the effect of other oab symptoms . frequency and 
 nocturia are most strongly associated with voided volumes recorded using the bladder 
 diary and filling cystometry . after multivariate analysis , urgency and urgency 
 incontinence symptoms were no longer significantly associated with most bladder 
 diary and filling cystometry parameters . female age was evidently associated with 
 nocturnal frequency episodes and volumes at first and normal desire to void.table 4results of multiple regression analysis from bladder diary and 
 filling cystometry parametersstandardized  coefficientsbladder diary measuresfilling cystometry measuresdfnfvol minvol maxvol meaniefdvndvsdvmccfrequency0.27 * 0.10*0.17*0.11*0.20 * 0.06*0.09*0.11*0.14*0.13*urgency0.08 * 0.020.010.05*0.030.010.08*0.08*0.050.04nocturia0.13 * 0.40*0.11*0.17*0.190.070.11*0.11*0.16*0.18*urge incontinence0.05*0.040.010.010.010.37*0.020.05*0.05*0.06*age0.05 * 0.17 * 0.05 * 0.010.010.05 * 0.18 * 0.17 * 0.07 * 0.04correlation coefficient ( adjusted 
 r)0.13 * 0.26 * 0.05 * 0.06 * 0.11 * 0.17 * 0.06 * 0.07 * 0.07 * 0.08*df : daytime frequency , nf : nocturnal frequency , volmin : minimum 
 voided volume , volmax : maximum voided volume , vol mean : mean voided volume , 
 ie : incontinence episodes , fdv : volume at first desire to void , ndv : volume at 
 normal desire to void , sdv : volume at strong desire to void , mcc : volume at 
 maximum cystometric capacity*p  <  0.05 results of multiple regression analysis from bladder diary and 
 filling cystometry parameters df : daytime frequency , nf : nocturnal frequency , volmin : minimum 
 voided volume , volmax : maximum voided volume , vol mean : mean voided volume , 
 ie : incontinence episodes , fdv : volume at first desire to void , ndv : volume at 
 normal desire to void , sdv : volume at strong desire to void , mcc : volume at 
 maximum cystometric capacity the aim of the current study was to assess the association between the oab 
 symptoms and objective parameters from a bladder diary and filling cystometry . of 
 all four oab symptoms the frequency symptom showed the strongest association with 
 daytime urinary frequency , nocturia with nocturnal frequency , and urgency 
 incontinence with incontinence episodes as measured in the bladder diary . the 
 frequency and nocturia symptoms showed almost equal and strong associations with 
 bladder volumes as measured in the bladder diary and by filling cystometry . the key 
 symptom of the oab syndrome , urgency , was either not at all or only poorly 
 associated with objective parameters from the bladder diary and filling 
 cystometry . the urgency symptom has been adopted as the key symptom of the oab syndrome . however , frequent day - time or night - time micturition may be perceived by women as 
 bothersome , even in the absence of urgency [ 14 , 15 ] . furthermore , 
 studies about health - related quality of life in women with oab report that the 
 presence of urgency alone is only associated with a moderate degree of bother 
 . ever since the introduction of 
 the oab syndrome into official standardized terminology , there has been an ongoing 
 debate about the accuracy and content of the definition of oab . the emphasis on 
 urgency as the key symptom is not based on a scientific factor and may have 
 originated from the introduction of the oab syndrome by the pharmaceutical industry 
 [ 17 , 18 ] . although the definition appears quite simple , it is 
 suggested that urgency might not be an  all or nothing  sensation . it is plausible 
 that there are different types of urgency that can be experienced and modulated in 
 various ways . the individual 
 perception of urgency makes it almost impossible to create a uniform definition for 
 the heterogeneous patient population with oab symptoms . because of the subjective 
 nature of the urgency symptom it is to be expected that associations with objective 
 parameters are limited . our results support this view . in many trials that evaluate 
 the treatment of oab , frequency and incontinence episodes , and not urgency , our results 
 support the use of frequency and incontinence episodes as outcome parameters in oab 
 studies , since these symptoms show the best associations between subjective and 
 objective parameters . it has also been previously demonstrated that the occurrence of the oab syndrome 
 is associated with objective parameters from the bladder diary and filling 
 cystometry [ 20 , 21 ] . however , these studies have not assessed 
 which of the symptoms contained in the official definition of the oab syndrome are 
 responsible for this effect . our results indicate that , after correction for the 
 presence of other symptoms , the association between oab and objective parameters is 
 mostly attributable to the voiding frequency and nocturia . as stated one limitation of the current study may be due to the differences in the 
 definition of urgency . the udi definition of urgency that we used is :  do you experience a strong feeling of urgency to empty your 
 bladder ?  . the current ics definition of urgency is :  complaint of a sudden , compelling desire to pass urine which is 
 difficult to defer  . these two definitions are not identical and therefore may not be interchangeable . 
 with respect to urgency incontinence therefore , we 
 can not be sure that women with stress incontinence at maximum cystometric capacity 
 responded positively to the urgency incontinence question . another possible limitation of our study is the fact that the study population 
 only consisted of women with urogenital dysfunction . consequently , the women without 
 a particularly bothersome oab symptom that were entered into the comparison group 
 ( group 1 ) were not entirely without symptoms , but did experience other symptoms of 
 urogenital dysfunction . this may have limited the differences we observed between 
 groups . however , despite this , the observed differences were not only statistically 
 significant , but also clinically relevant as shown by our effect size statistics . if 
 we had used a completely healthy control group , the differences were likely to have 
 been even more pronounced . finally , we used a 48-h bladder diary , which is known to be less accurate than a 
 bladder diary that covers 37  days . however , it has been demonstrated that a prolonged duration of 
 bladder diary recording is associated with lower compliance and higher burden for 
 the patient [ 23 , 24 ] . daytime and nocturnal frequency symptoms are best associated with objective 
 frequency and volume parameters from a bladder diary and filling cystometry . in 
 contrast , the urgency symptom , which is essential in the current definition of oab , 
 is poorly associated with these objective parameters . therefore , the current 
 practice of using frequency and incontinence episodes in the outcome research of oab 
 trials is justified . this article is distributed under the terms of the creative commons 
 attribution license which permits any use , distribution , and reproduction in any 
 medium , provided the original author(s ) and the source are credited .
introduction and hypothesisa study was conducted to assess associations between different overactive 
 bladder ( oab ) symptoms and their outcomes on bladder diary and filling cystometry 
 parameters.methodswe performed a retrospective cohort study in database of 6,876 urinary 
 distress inventories , 3,185 bladder diaries and 2,153 filling cystometries from 
 women referred to our urogynecological center between 2003 and 2009 . 
 women were 
 dichotomized into two groups . 
 group i : those women without symptoms , and those 
 with symptoms that were not bothersome . 
 group ii : women with bothersome symptoms . 
 data obtained from bladder diaries were : daytime urinary frequency , nocturnal 
 frequency , minimum voided volume , maximum voided volume , average voided volume , 
 and incontinence episodes . from filling cystometries , volumes at first desire to 
 void , normal desire to void , strong desire to void and maximum cystometric 
 capacity , were extracted . 
 univariate and multiple linear regression analysis were 
 performed to determine associations between oab symptoms and bladder diary and 
 filling cystometry measurements.resultsafter multivariate analysis the objective daytime frequency was most strongly 
 associated with the frequency symptom (  0.27 , 
 p  <  0.05 ) , night time frequency with the nocturia symptom (  
 0.40 , p  <  0.05 ) and the number of 
 incontinence episodes with the urge incontinence symptom (  0.37 , p  <  0.05 ) . 
 both frequency and nocturia symptoms 
 were significantly associated with bladder diary and cystometry filling volumes , 
 and their effect size was the same . the urgency symptom proved 
 to be poorly 
 associated with objective parameters.conclusionsin contrast to the frequency and nocturia symptom , the urgency symptom is 
 poorly associated with objective parameters on bladder diary and filling 
 cystometry . therefore , the current practice of using frequency and incontinence 
 episodes in outcome research of oab trials is justified .