Estimating Minimally Important Differences for the Bladder Cancer Index Using Distribution and Anchor Based Approaches

• Published in: The Journal of urology Vol. 201; no. 4; pp. 709 - 714
• Main Authors: Peyton, Charles C, Henriksen, Carl, Reich, Richard R, Azizi, Mounsif, Gilbert, Scott M
• Format: Journal Article
• Language: English
• Published: United States 01-04-2019
• Subjects: Aged; Cystectomy; Diagnostic Self Evaluation; Female; Humans; Longitudinal Studies; Male; Middle Aged; Patient Reported Outcome Measures; Prospective Studies; Quality of Life; Urinary Bladder Neoplasms - complications; Urinary Bladder Neoplasms - physiopathology; Urinary Bladder Neoplasms - surgery; cystectomy; bladder neoplasms; patient reported outcome measures; quality of life; minimal clinically important difference
• ISSN: 0022-5347; 1527-3792
• DOI: 10.1016/j.juro.2018.10.008

The BCI (Bladder Cancer Index) is a validated, condition specific health questionnaire assessing urinary, bowel and sexual function and quality of life among patients with bladder cancer. We aimed to establish minimally important difference score thresholds that signal clinical importance.
For 1 year after surgery we followed a prospective cohort of 150 patients who underwent radical cystectomy between 2013 and 2016. Usable data on 138 patients were analyzed. The BCI and the Medical Outcomes Study SF-36 (36-Item Short Form Health Survey) questionnaires were completed prior to cystectomy, and 3, 6 and 12 months postoperatively. Distribution based, minimally important differences were estimated at ⅓ and ½ SD for each index domain across time points. Changes in index domain scores anchored to changes in a SF-36 overall health assessment question were used to estimate anchor based, minimally important differences. Pooled averages are reported between time points and methods.
The distribution based, minimally important difference of ⅓ SDs for urinary, bowel and sexual domains ranged between 5.3 and 7.3, 4.6 and 5.6, and 6.0 and 8.9 points, respectively. Ranges of ½ SDs were 8.8 and 10.9, 6.8 and 8.4, and 8.9 and 13.5 points, respectively. The anchor based approach resulted in minimally important difference estimates of 6.2, 7.3 and 6.8 points, respectively. Aggregated results across the 2 approaches resulted in minimally important differences of 6 to 9, 5 to 8 and 7 to 11 points for urinary, bowel and sexual domains, respectively.
Using 2 independent approaches to our knowledge we established the first minimally important difference estimates for the BCI. Defining patient reported outcome thresholds is important to interpret changes or differences in BCI scores.