Null Hypothesis Of Difference Research Articles

Paper 12: Severity of Chondrolabral Junction Degeneration Predicts Conversion to Total Hip Arthroplasty after Arthroscopic Femoroacetabular Impingement Treatment at Minimum 10-Years Follow-Up

Objectives: To identify location and severity of intraoperative pathology at time of arthroscopic surgery for femoroacetabular impingement (FAI) as risk factors for conversion to total hip arthroplasty (THA) utilizing long-term follow-up (minimum 10 years). Methods: Retrospective study of prospectively collected data of adult patients (≥ 18 years) who underwent hip arthroscopy for FAI between 1998 and 2011 with minimum follow-up of 10 years. Location and severity of pathology at time of arthroscopic surgery were assessed as risk factors for later conversion to a primary outcome of THA. Patients with radiographic evidence of hip dysplasia and previous history of hip surgery were excluded. Patients were then grouped according to whether they had underwent THA. Differences in continuous variables including age, BMI, and center edge angle (CEA) were analyzed with independent t tests. Differences in categorical variables including type of treatment (debridement or repair), deformity (CAM vs pincer vs combined), Outerbridge grade, location of most severe chondral wear (anterosuperior acetabulum, posterosuperior acetabulum, femoral head), presence of chondral flap, and degree of chondrolabral degeneration (as measured by Beck classification) were analyzed with the Pearson’s Chi-squared test. For variables with greater than two levels (chondrolabral degeneration, etc.) adjusted residuals were calculated to determine which comparisons were statistically different, with a value of >2 indicating a lack of fit with the null hypothesis of difference. A multivariable logistic regression model was constructed to estimate the influence of the exact location and severity of pathology on risk for conversion to THA. Model results are reported as odds ratios (OR) with corresponding 95% confidence intervals. Results: A total of 109 patients with a mean age of 39.41 ± 11.43 years and minimum follow-up of 10 years were eligible for inclusion in this study. The average follow-up was 12.29 ± 2.53 years. Average body mass index (BMI) was 26.19 ± 4.07 while average center edge angle (CEA) was 39.53 ± 7.24. 67 (61.5%) patients underwent debridement while 42 (38.5%) patients underwent labral repair. 32 (29.4%) patients subsequently converted to THA. BMI (1.7% difference, p = 0.072), CEA (0.3% difference, p = 0.832), sex (0.2% difference, p = 0.991), procedure type (11.8% difference, p = 0.565), and presence of a chondral flap (6.3% difference, p = 0.685) were not significantly associated with conversion to THA. FAI type, Outerbridge grade, chondrolabral junction degeneration, and location of most severe degenerative change were statistically significant, with adjusted residuals greater than 2 (Table 1). A multivariable logistic regression model demonstrated age (OR=1.08, 95% CI 1.03-1.14, p = 0.002), Grade 4 chondrolabral degeneration (OR = 3.26, 95% CI 1.16-9.17, p = 0.025) and combined FAI type (OR = 4.32, 95% CI 1.38 – 13.56, p = 0.012) as significant risk factors for conversion to THA. Conclusions: Grade 4 degeneration of the chondrolabral junction as well as combined FAI type and older age are significant risk factors for conversion to THA after arthroscopic treatment of FAI at minimum 10-years of follow-up. [Table: see text][Table: see text]

Faster pediatric 3-T abdominal magnetic resonance imaging: comparison between conventional and variable refocusing flip-angle single-shot fast spin-echo sequences.

Single-shot fast spin echo (SSFSE) is particularly appealing in pediatric patients because of its motion robustness. However radiofrequency energy deposition at 3 tesla forces long pauses between slices, leading to longer scans, longer breath-holds and more between-slice motion. We sought to learn whether modulation of the SSFSE refocusing flip-angle train could reduce radiofrequency energy deposition without degrading image quality, thereby reducing inter-slice pauses and overall scan times. We modulated the refocusing flip-angle train for SSFSE to minimize energy deposition while minimizing blurring and motion-related signal loss. In a cohort of 50 consecutive patients (25 boys, mean age 5.5years, range 1month to 17years) referred for abdominal MRI we obtained standard SSFSE and variable refocusing flip-angle (vrfSSFSE) images and recorded sequence scan times. Two readers independently scored the images in blinded, randomized order for noise, tissue contrast, sharpness, artifacts and left lobe hepatic signal uniformity on a four-point scale. The null hypothesis of no difference between SSFSE and vrfSSFSE image-quality was assessed with a Mann-Whitney U test, and the null hypothesis of no scan time difference was assessed with the paired t-test. SSFSE and vrfSSFSE mean acquisition times were 54.3 and 26.2s, respectively (P-value <0.0001). For each reader, SSFSE and vrfSSFSE noise, tissue contrast, sharpness and artifacts were not significantly different (P-values 0.18-0.86). However, SSFSE had better left lobe hepatic signal uniformity (P < 0.01, both readers). vrfSSFSE is twice as fast as SSFSE, with equivalent image quality with the exception of left hepatic lobe signal heterogeneity.

Demostración de equivalencia terapéutica previa al análisis de minimización de costes

Despite its simplicity, cost-minimization analysis (CMA) is rarely used. This is because the prior statement of equal therapeutic effectiveness between the alternatives is often based on weak evidence, the reason being, in most cases, that no rejection of the null hypothesis of difference is misinterpreted as an affirmation of the nullity hypothesis. This assumption is wrong and dependent on sample size; so a cost-effectiveness analysis is preferred. However, the CMA is a legitimate option when a lack of clinical difference between the alternatives has been previously proved. The equivalence analysis based on two simultaneous one side test procedures or on a graphical representation can be used as a guide for

비열등성 임상시험에서 독립인 두 비율 차 검정에 대한 비교 연구

두 비율비교 비열등성 임상시험(non-inferiority trial)에서의 검정은 두 비율간에 차이가 없다는 영가설에 근거한 정규근사 산출식이 흔히 사용 된다. 본 연구에서는 두 비율차이가 영이 아니라는 가설에서 유도된 Miettinen과 Nurminen이 제안한 우도 스코어검정(likelihood score test)과 Farrington과 Manning의 검정 그리고 비대칭도(skewness)을 보정한 Gart와 Nam이 제안한 검정방법을 소개하고 모의실험을 통하여 제 1종 오류와 검정력을 비교하여 비열등성 임상시험에서 검정방법의 결정에 가이드라인을 제시하고자 한다. Normal approximation methods under the null hypothesis of no difference are frequently used to test the two independent proportions in non-inferiority trials. However, these tests are not appropriate under the null hypothesis of non-zero difference. We review the likelihood score methods proposed by Miettinen and Nurminen, Farrington and Manning, and Gart and Nam and compare the performance of these tests. The simulation study shows that the likelihood score tests under the null hypothesis of non-zero difference have better performance at a Type I error and power than usual normal approximation methods.

Reporting Results of Orthopaedic Research: Confidence Intervals and p Values

Reporting Results of Orthopaedic Research: Confidence Intervals and p Values

Sample size determination in stratified trials to establish the equivalence of two treatments

When designing a trial to establish that a new treatment is as effective as a standard one, the conventional test procedure and sample size based on a null hypothesis of no difference between two treatments is inappropriate. Several authors have investigated test statistics and corresponding sample sizes based on the null hypothesis that the standard treatment is more effective than the new by at least some specific value for a single 2 x 2 table. This paper considers a trial that involves several 2 x 2 tables and presents an approximate formula for the sample size required to obtain a given power of a one-tailed score test for a null hypothesis of a specific common non-zero difference between two treatments across strata. I show that the sample size for a trial based on an unstratified test is always larger than that based on a stratified test when the design is balanced.