{"id":1807,"date":"2018-09-12T13:12:53","date_gmt":"2018-09-12T13:12:53","guid":{"rendered":"https:\/\/blogs.bmj.com\/bmjebmspotlight\/?p=1807"},"modified":"2022-01-19T15:13:01","modified_gmt":"2022-01-19T15:13:01","slug":"tvy-seventeen-year-follow-up-and-the-misleading-effect","status":"publish","type":"post","link":"https:\/\/blogs.bmj.com\/bmjebmspotlight\/2018\/09\/12\/tvy-seventeen-year-follow-up-and-the-misleading-effect\/","title":{"rendered":"TVT: seventeen year follow up and the shrinking denominator effect"},"content":{"rendered":"

 <\/p>\n

The shrinking denominator enhances the effect size and misleads the reader into thinking the effect is better than it actually is.<\/em><\/p>\n

Carl Heneghan<\/p>\n

\n

\"\"<\/p>\n

I am at the Ideal Conference<\/a>, at a workshop talking about clinical trial reporting and recent surgical scandals.\u00a0 I chose the\u00a017 years\u00a0follow-up of the Tension-free Vaginal Tape – often quoted – as one example of the significant problems with long-term outcome reporting.<\/p>\n

Here is what\u00a0the Oxford Clinical Commissioning\u00a0Group<\/a> report: ‘it confers a high prospect of long term cure (published 17 year data shows 70-80% long term efficacy) with a low risk of complication;’\u00a0 the Cochrane review<\/a> on mid-urethral review reports: ‘Observational studies of MUS show data confirming effectiveness in the long term with some data that cover 15 to 17 years’ and a literature review<\/a> on De Novo Urgency reports: ‘the reported success rates for this procedure are high, results reported at seventeen year\u2019s follow up indicate a 90% objective cure.’<\/p>\n

Sound good, doesn’t it?<\/p>\n

The original trial was done in three Nordic centres, and upon reading the trial publications closely (I found reports at 5,7,11 and 17 years of follow-up) what you find is a small study of 90\u00a0women\u00a0and a denominator that shrinks over time. The shrinking denominator enhances the effect size and misleads the reader into thinking the effect is better than it actually is.<\/p>\n

 <\/p>\n

\"\"<\/strong><\/p>\n

 <\/p>\n

Here’s the summary of the four trial publications with 5, 7, 11 and 17 years of follow-up.<\/p>\n

2005 publication (Five-year follow-up first published as a supplement in 2001)<\/strong><\/p>\n

The study population consisted of 90 consecutive patients who were enrolled in a\u00a0prospective multicenter trial in three Nordic centres between 1st<\/sup> January 1995 and 15th<\/sup> \u00a0October 1996. Of these 90 women, 85 (%) could be evaluated after five years according to the protocol (five had to be interviewed by phone) 72 of the 85 patients were assessed (85%) as cured; 9 patients (10.6%) were significantly improved and 4 (4.7%) were regarded as failures.<\/p>\n

2007 publication (Seven-year follow up):<\/strong><\/p>\n

The study population consisted of the same 90 women, but now only 80 (89%) were followed up: 3 had died, 6 lived in nursing homes, being disabled to the degree that they could not be evaluated, and 1 woman was completely lost to follow-up. You could have\u00a0reported this results as 10% of women had\u00a0died or been fatally\u00a0disabled; but instead, objective and subjective cure rates were reported as 81%.<\/p>\n

2008 publication (Eleven Year follow\u00a0up):<\/strong><\/p>\n

One year later the\u00a0eleven-year follow-up was published with the same 90 women. Now only 69 (77 %) women could be assessed: 53 women were seen at the clinics and 16 contacted outside the clinics, and\u00a077% (53\/69) regarded themselves as cured.<\/p>\n

2013 (Seventeen years follow up):<\/strong><\/p>\n

The study consisted of the 90 women, but only 58 (64%) women could be invited to visit the clinics, and 46 women were assessed according to the clinical protocol.\u00a0 But, look what\u00a0happens. Suddenly cure rates get better: 42 out of 46 women (91.3 %)\u00a0stated they were cured. This is backed up in the abstract, which reports: ‘Over 90 % of the women were objectively continent.’<\/p>\n

The shrinking denominator<\/strong><\/p>\n

The shrinking denominator effect happens when\u00a0you\u00a0fail to include all of the patients in the analysis, an intention to\u00a0treat (ITT) analysis would include all 90 women.\u00a0In an ITT\u00a0 analysis, the results are based on all those initially assigned to the intervention and it leads to smaller effects because the denominator is often much larger than the group followed up. With all the data less than half of the women\u00a0(42\/90; 47%)<\/span>\u00a0would be\u00a0<\/span>cured.<\/p>\n

\n

References:<\/p>\n

Mid-urethral sling operations for stress urinary incontinence in women.\u00a0<\/a>Ford AA, Rogerson L, Cody JD, Aluko P, Ogah JA.\u00a0<\/span>Cochrane Database Syst Rev<\/span>. 2017 Jul 31;7:CD006375. doi: 10.1002\/14651858.CD006375.pub4.\u00a0<\/span><\/p>\n

Seventeen years’ follow-up of the tension-free vaginal tape procedure for female stress urinary incontinence.\u00a0<\/a>Nilsson CG, Palva K, Aarnio R, Morcos E, Falconer C.\u00a0<\/span>Int Urogynecol J<\/span>. 2013 Aug;24(8):1265-9. doi: 10.1007\/s00192-013-2090-2.\u00a0<\/span><\/p>\n

\n
\n
\n
\n

Eleven years prospective follow-up of the tension-free vaginal tape procedure for treatment of stress urinary incontinence.\u00a0<\/a>Nilsson CG, Palva K, Rezapour M, Falconer C.\u00a0<\/span>Int Urogynecol J Pelvic Floor Dysfunct<\/span>. 2008 Aug;19(8):1043-7. <\/span>doi: 10.1007\/s00192-008-0666-z.\u00a0<\/span><\/p>\n

Seven-year follow-up of the tension-free vaginal tape procedure for treatment of urinary incontinence.\u00a0<\/a>Nilsson CG, Falconer C, Rezapour M.\u00a0<\/span>Obstet Gynecol<\/span>. 2004 Dec;104(6):1259-62.<\/span><\/p>\n

Long-term results of the tension-free vaginal tape (TVT) procedure for surgical treatment of female stress urinary incontinence.\u00a0<\/a>Nilsson CG, Kuuva N, Falconer C, Rezapour M, Ulmsten U. I<\/span>nt Urogynecol J Pelvic Floor Dysfunct<\/span>. 2001;12 Suppl 2<\/span>:S5-8.<\/span><\/p>\n

\n

BMJ\u00a0Evidence-Based Medicine<\/a>\u00a0\u2013\u00a0original evidence-based research, insights and opinion<\/p>\n

Read more in the\u00a0Welcome to BMJ Evidence-Based Medicine Editorial<\/a>.<\/p>\n

\"\"<\/p>\n

\n

Competing interests<\/b><\/p>\n

Carl has received expenses and fees for his media work including BBC Inside Health. He holds grant funding from the NIHR, the NIHR School of Primary Care Research, The NIHR Oxford BRC\u00a0 and the WHO. He has also received income from the publication of a series of toolkit books. CEBM jointly runs the\u00a0EvidenceLive<\/a>\u00a0Conference with the BMJ and the\u00a0Overdiagnosis Conference<\/a>\u00a0with some international partners which are based on a\u00a0 non-profit model. he is a clinical advisor to the UK Gov\u2019ts All Party Parliamentary Group (APPG) on surgical mesh.<\/p>\n

 <\/dd>\n<\/dl>\n<\/div>\n<\/div>\n

<\/p>\n","protected":false},"excerpt":{"rendered":"

  The shrinking denominator enhances the effect size and misleads the reader into thinking the effect is better than it actually is. Carl Heneghan I am at the Ideal Conference, at a workshop talking about clinical trial reporting and recent surgical scandals.\u00a0 I chose the\u00a017 years\u00a0follow-up of the Tension-free Vaginal Tape – often quoted – […]<\/p>\n

Read More…<\/a><\/p>\n","protected":false},"author":1,"featured_media":1762,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[14374,14388],"tags":[],"class_list":["post-1807","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-carl-heneghan","category-evidence-watch"],"yoast_head":"\nTVT: seventeen year follow up and the shrinking denominator effect - BMJ EBM Spotlight<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/blogs.bmj.com\/bmjebmspotlight\/2018\/09\/12\/tvy-seventeen-year-follow-up-and-the-misleading-effect\/\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"TVT: seventeen year follow up and the shrinking denominator effect - BMJ EBM Spotlight\" \/>\n<meta property=\"og:description\" content=\"  The shrinking denominator enhances the effect size and misleads the reader into thinking the effect is better than it actually is. 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