Power and sample size calculations for generalized regression models with covariate measurement error

Covariate measurement error is often a feature of scientific data used for regression modelling. The consequences of such errors include a loss of power of tests of significance for the regression parameters corresponding to the true covariates. Power and sample size calculations that ignore covariate measurement error tend to overestimate power and underestimate the actual sample size required to achieve a desired power. In this paper we derive a novel measurement error corrected power function for generalized linear models using a generalized score test based on quasi-likelihood methods. Our power function is flexible in that it is adaptable to designs with a discrete or continuous scalar covariate (exposure) that can be measured with or without error, allows for additional confounding variables and applies to a broad class of generalized regression and measurement error models. A program is described that provides sample size or power for a continuous exposure with a normal measurement error model and a single normal confounder variable in logistic regression. We demonstrate the improved properties of our power calculations with simulations and numerical studies. An example is given from an ongoing study of cancer and exposure to arsenic as measured by toenail concentrations and tap water samples.     

Children and guns in a well child cohort

BACKGROUND: The purpose of this study was to estimate the extent of and to identify predictors of preadolescent gun use in a well child cohort with matched parent and child data. METHODS: We analyzed self-report questionnaires from children and their parents using conditional logistic regression models. Questionnaires were given to 3,145 ten- to twelve-year-old children and 3,145 parents enrolled by their pediatricians in a prevention cohort study. RESULTS: Thirty-two percent of the children lived in households with guns. Children and parents generally agreed about the presence of guns in their homes; 17% had access to unlocked guns in their homes; 22% had fired guns. In this preadolescent cohort, firing guns was associated with being male, having guns in the home, having friends who use guns, and initiation of alcohol use. CONCLUSIONS: In this well child cohort, significant numbers of preadolescent, healthy boys in white, middle-class U.S. homes have access to guns, are using guns, and have friends who use guns. These children are also early alcohol adopters. Safety interventions with parents of preadolescents about the risks for accidental injury, death, and suicide due to child gun use may prove beneficial.     

氯喹对烟雾吸入伤大鼠肺细胞膜ATP酶活性和丙二醛含量的影响

目的：探讨氯喹对烟雾吸入伤大鼠肺细胞膜ＡＴＰ酶活性及丙二醛含量的影响,方法：８０只Ｗｉｓｔａｒ大鼠随机分成正常对照组,烟雾吸入伤１,３,６,１２和２４ｈ组以及氯喹治疗６ｈ和１２ｈ组,分别于各时相点活杀动物,取肺制备膜制剂,用生化比色法测定膜上Ｎａ＾＋,Ｋ＾＋－ＡＴＰ酶Ｍｇ＾２＋－ＡＴＰ酶和Ｃａ＾２＋－ＡＴＰ酶活性,用比色法测定膜上丙醛含量,并用定磷法测定膜总磷脂含量,结果：烟雾吸入伤后,肺细胞膜３     

中频交变磁场照射后小鼠的行为学变化

目的:目前电磁辐射对生物体行为学方面的研究还很薄弱,设立不同磁场的强度和不同照射的周期,观察中频领域磁场照射对小鼠的自主活动和学习记忆的影响。方法:实验于2007-05-10/06-15在清华大学医学院和中国医学科学院药用植物研究所完成。①实验材料:磁场发生装置:中频交变磁场发生装置由清华大学工程物理系医学物理与工程研究所自主研发,可产生频率为40kHz,场强为28.8A/m,28.8kA/m的中频交变磁场。自主活动测试箱:中国医学科学院药用植物研究所提供,为一可封闭的金属箱,内置摄像头。4只黑色塑料测试桶分别置于箱子四角。水迷宫测试箱:中国医学科学院药用植物研究所提供。②实验动物及方法:将80只小鼠随机分为不同场强照射组和对照组。强磁场照射1组:11.6kA/m/40kHz,1h/d,连续照射7d。强磁场照射2组:11.6kA/m/40kHz,2h/d,连续照射7d。强磁场照射3组:11.6kA/m/40kHz,2h/d连续照射15d。弱磁场照射组:28.8kA/m/40kHz,2h/d,连续照射7d。对照组除了未放入磁场照射,其他条件与照射组一致。实验过程中对动物处置符合动物伦理学要求。③实验评估:观察其一般活动的改变,并采用自主活动测试箱和水迷宫测试箱进行测试,观察各组小鼠的自主活动和学习记忆的改变。结果:①一般行为观察:与对照组小鼠对比,经过中频交变磁场照射过的各组小鼠活跃度减低,毛色较差。强磁场照射3组(145G,2h/d,连续15d)于第11天和13天分别死亡1只。②自主活动检测结果:强磁场照射2,3组小鼠的运动路程、运动速度、运动时间明显低于对照组(P<0.05)。③水迷宫测试结果:在学习记忆检测阶段撤掉平台,发现各组动物2min内穿越平台原来所在象限的次数没有明显差别(P>0.05)。结论:中频交变磁场照射会给小鼠的自发活动造成一定影响,对学习记忆没有影响。     

Titanium elastic nailing in femoral diaphyseal fractures of children in 6-16 years of age

Background:

Management of femoral diaphyseal fractures in the age group of 6-16 years is controversial. There has been a resurgence worldwide for operative fixation.

Materials and Methods:

Twenty-two children (18 boys, 4 girls) aged 6-16 years with recent (> 3 days) femoral diaphyseal fractures (20 closed, 2 open) were stabilized with Titanium Elastic Nail (TEN). These fractures were in proximal third (n=3), middle third (n=15) and in the distal third (n=4) 17 patients underwent surgery within seven days of their injury. The results were evaluated using Flynn''s scoring criteria. Statistical analysis was done using Fischer''s exact test.

Results:

All 22 patients were available for evaluation after a mean of 26 months (14-36 months) of followup. Radiological union in all cases were achieved in a mean time of 8.7 weeks. Full weight bearing was possible in a mean time of 8.8 weeks. Mean duration of hospital stay was 9.8 days. The results were excellent in 13 patients (59.0%), successful in six (27.2%) and poor in three patients (13.6%). All patients had early return to school.

Conclusion:

Intramedullary fixation titanium elastic nailing is an effective treatment of diaphyseal fractures of the femur in properly selected patients of the 6-16 years age group.     

Cost-effective osteoporosis treatment thresholds: the United States perspective

Summary A United States-specific cost-effectiveness analysis, which incorporated the cost and health consequences of clinical fractures of the hip, spine, forearm, shoulder, rib, pelvis and lower leg, was undertaken to identify the 10-year hip fracture probability required for osteoporosis treatment to be cost-effective for cohorts defined by age, sex, and race/ethnicity. A 3% 10-year risk of hip fracture was generally required for osteoporosis treatment to cost less than $60,000 per QALY gained. Introduction Rapid growth of the elderly United States population will result in so many at risk of osteoporosis that economically efficient approaches to osteoporosis care warrant consideration. Methods A Markov-cohort model of annual United States age-specific incidence of clinical hip, spine, forearm, shoulder, rib, pelvis and lower leg fractures, costs (2005 US dollars), and quality-adjusted life years (QALYs) was used to assess the cost-effectiveness of osteoporosis treatment ($600/yr drug cost for 5 years with 35% fracture reduction) by gender and race/ethnicity groups. To determine the 10-year hip fracture probability at which treatment became cost-effective, average annual age-specific probabilities for all fractures were multiplied by a relative risk (RR) that was systematically varied from 0 to 10 until a cost of $60,000 per QALY gained was observed for treatment relative to no intervention. Results Osteoporosis treatment was cost-effective when the 10-year hip fracture probability reached approximately 3%. Although the RR at which treatment became cost-effective varied markedly between genders and by race/ethnicity, the absolute 10-year hip fracture probability at which intervention became cost-effective was similar across race/ethnicity groups, but tended to be slightly higher for men than for women. Conclusions Application of the WHO risk prediction algorithm to identify individuals with a 3% 10-year hip fracture probability may facilitate efficient osteoporosis treatment. The authors comprise the National Osteoporosis Foundation Guide Committee.     

Anterior compartment pressure measurement in closed fractures of leg

Background:

Compartment syndrome is a potentially devastating condition. Increased intracompartmental pressure has been incriminated as the primary pathogenic factor in compartment syndrome. The purpose of this prospective study was to monitor the anterior compartmental pressure and differential pressure to minimize the incidence of acute compartment syndrome.

Materials and Methods:

Seventy-five consecutive cases of closed fractures of leg presenting within six hours of injury were taken for measurement of anterior compartment pressure at the level of fracture and at 5 cm and 10 cm away from the fracture site, using the Whitesides'' infusion technique. A differential pressure of less than 30 mm Hg was taken as the criterion for diagnosis of compartment syndrome.

Results:

Two patients (2.67%) developed acute compartment syndrome. The mean anterior compartment pressures were highest at the level of the fracture and went on decreasing as we went away from the fracture site, which was found to be statistically significant (P < 0.001).

Conclusion:

Compartment pressure measurement is the most reliable and objective method for early diagnosis of compartment syndrome. Whitesides'' infusion technique is a relatively easy and inexpensive method to come to a diagnosis of compartment syndrome in a developing country like India. Differential pressure is more reliable than absolute pressure in predicting the development of an impending compartment syndrome.     

Predictors of Long-Term Opioid Use Among Patients With Painful Lumbar Spine Conditions

Our objective was to assess predictors of self-reported opioid use among patients with back pain due to lumbar disc herniation or spinal stenosis. Data were from the Spine Patient Outcomes Research Trial (SPORT), a multi-site observational study and randomized trial. We examined characteristics shown or hypothesized to be associated with opioid use. Using generalized estimating equations, we modeled associations of each potential predictor with opioid use at 12 and 24 months. At baseline, 42% of participants reported opioid use. Of these participants, 25% reported continued use at 12 months and 21% reported use at 24 months. In adjusted models, smoking (RR = 1.9, P < .001 at 12 months; RR = 1.5, P = .043 at 24 months) and nonsurgical treatment (RR = 1.7, P < .001 at 12 months; RR = 1.8, P = .003 at 24 months) predicted long-term opioid continuation. Among participants not using opioids at baseline, incident use was reported by 8% at 12 months and 7% at 24 months. We found no significant predictors of incident use at 12 or 24 months in the main models. In conclusion, nonsurgical treatment and smoking independently predicted long-term continued opioid use. To our knowledge, this is the first longitudinal study to assess predictors of long-term and incident opioid use among patients with lumbar spine conditions.PerspectiveThis longitudinal study of patients with disc herniation or spinal stenosis found that nonsurgical treatment and smoking predicted long-term self-reported opioid use. The greater risk of opioid continuation with nonsurgical therapy may be helpful in decision-making about treatment. The relationship between opioid use, smoking, and other substance use deserves further study.