Neurourology and Urodynamics 25:743 (2006) EDITORIAL COMMENT Re: Podnar S, Barbic M. 2006. Non-Neurogenic Urinary Retention (Fowler’s Syndrome) inTwo Sisters. Neurourol Urodynam 25:739^741 There are a lot of assumptions made in the calculation of the probability of two sisters having the same problem, which are not made clear, and I think some of them are an oversimpli¢- cation. The ¢rst is that moving from an incidence rate of 0.2 per 100,000 to a lifetime prevalence of10 per 100,000, assumes a uniform incidence over a 50-year period in women’s lives. Since this syndrome is related to the ovaries then there would be a higher incidence in the reproductive years and lower incidence outside these years.The e¡ect of building this into their model would likely be that the lifetime incidence is lower than10 per100,000,which would make it even rarer than they suggest. The next point to note is that multiplying probabilities assumes that the probabilities are independent, however the authors argue that the probabilities of two sisters both having Fowler’s syndrome are not independent. To be correct the authors should state before doing multiplication that this is what would happen if there was independence. The way the authors work out the number of families with two sisters in them oversimpli¢es the issue. It is more statisti- cally correct to calculate this by the weighted average of the probabilities of having two sisters over all family sizes weighted by the proportion of families that size. The overall e¡ect of these simpli¢cations made by the authors is likely to be conservative. Finding two sisters with Fowler’s syndrome is even less likely to be due to chance that the calculation would imply. PeterHerbison* Dunedin,NewZealand The author could not be contacted about potential con£icts of interest. The views expressed in editorials and editorial comments are not necessarily representative of the views of the International Continence Society. *Correspondence to: Peter Herbison, Department of Preventive and Social Medicine, Dunedin School of Medicine, P.O. Box 913, Dunedin, New Zealand. E-mail: [email protected] Published online 8 August 2006 inWiley InterScience (www.interscience.wiley.com) DOI 10.1002/nau.20290 ß 2006Wiley-Liss,Inc.

Re: Podnar S, Barbic M. 2006. Non-neurogenic urinary retention (Fowler's syndrome) in two sisters. Neurourol Urodynam 25:739–741

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Page 1: Re: Podnar S, Barbic M. 2006. Non-neurogenic urinary retention (Fowler's syndrome) in two sisters. Neurourol Urodynam 25:739–741

Neurourology and Urodynamics 25:743 (2006)

EDITORIALCOMMENT

Re: Podnar S, Barbic M. 2006. Non-Neurogenic UrinaryRetention (Fowler’s Syndrome) in Two Sisters.

Neurourol Urodynam 25:739^741

There are a lot of assumptions made in the calculation of theprobability of two sisters having the same problem, which arenot made clear, and I think some of them are an oversimpli¢-cation. The ¢rst is that moving from an incidence rate of0.2 per100,000 to a lifetime prevalence of10 per100,000, assumesa uniform incidence over a 50-year period in women’s lives.

Since this syndrome is related to the ovaries then therewould be a higher incidence in the reproductive years andlower incidence outside these years.The e¡ect of building thisinto their model would likely be that the lifetime incidence islower than10 per100,000,whichwouldmake it even rarer thanthey suggest.

The next point to note is that multiplying probabilitiesassumes that the probabilities are independent, however theauthors argue that the probabilities of two sisters both having

Fowler’s syndrome are not independent. To be correct theauthors should state before doing multiplication that this iswhat would happen if there was independence.The way the authors work out the number of families with

two sisters in them oversimpli¢es the issue. It is more statisti-cally correct to calculate this by the weighted average of theprobabilities of having two sisters over all family sizesweighted by the proportion of families that size.The overall e¡ect of these simpli¢cations made by the

authors is likely to be conservative. Finding two sisters withFowler’s syndrome is even less likely to be due to chance thatthe calculation would imply.

PeterHerbison*Dunedin,NewZealand

The author could not be contacted about potential con£icts of interest.The views expressed in editorials and editorial comments are not necessarilyrepresentative of the views of the International Continence Society.*Correspondence to: Peter Herbison, Department of Preventive andSocial Medicine, Dunedin School of Medicine, P.O. Box 913, Dunedin,New Zealand. E-mail: [email protected] online 8 August 2006 inWiley InterScience(www.interscience.wiley.com)DOI 10.1002/nau.20290

�2006Wiley-Liss, Inc.