The many weak instruments problem and Mendelian randomization

Instrumental variable estimates of causal effects can be biased when using many instruments that are only weakly associated with the exposure. We describe several techniques to reduce this bias and estimate corrected standard errors. We present our findings using a simulation study and an empirical application. For the latter, we estimate the effect of height on lung function, using genetic variants as instruments for height. Our simulation study demonstrates that, using many weak individual variants, two‐stage least squares (2SLS) is biased, whereas the limited information maximum likelihood (LIML) and the continuously updating estimator (CUE) are unbiased and have accurate rejection frequencies when standard errors are corrected for the presence of many weak instruments. Our illustrative empirical example uses data on 3631 children from England. We used 180 genetic variants as instruments and compared conventional ordinary least squares estimates with results for the 2SLS, LIML, and CUE instrumental variable estimators using the individual height variants. We further compare these with instrumental variable estimates using an unweighted or weighted allele score as single instruments. In conclusion, the allele scores and CUE gave consistent estimates of the causal effect. In our empirical example, estimates using the allele score were more efficient. CUE with corrected standard errors, however, provides a useful additional statistical tool in applications with many weak instruments. The CUE may be preferred over an allele score if the population weights for the allele score are unknown or when the causal effects of multiple risk factors are estimated jointly. © 2014 The Authors. Statistics in Medicine published by John Wiley & Sons Ltd.     

Instruments for detection and screening of cognitive impairment for older adults in primary care settings: A review

The Patient Protection and Affordable Care Act requires evaluation for cognitive impairment as part of the Annual Wellness Visit (AWV). Nurses and nurse practitioners in primary care are in a good position to incorporate brief cognitive screens into the AWV. Early recognition of cognitive problems allows clinicians and patients the opportunity to discuss any new or ongoing concerns about cognition, address possible reversible causes, or refer for further evaluation. It should be noted that some patients may prefer not to explore for cognitive impairment.Numerous brief cognitive screens have been developed for primary care, with no one screen being appropriate for all patients or clinicians. This review examines the psychometric properties, usefulness, and limitations of both patient and informant brief (under five minutes) cognitive screens endorsed by the Alzheimer's, National Institute of Aging (NIA), and Gerontological Society (GSA) workgroups, plus a recently developed brief version of the standard MoCA.     

Cost-effectiveness of Chlamydia Vaccination Programs for Young Women

We explored potential cost-effectiveness of a chlamydia vaccine for young women in the United States by using a compartmental heterosexual transmission model. We tracked health outcomes (acute infections and sequelae measured in quality-adjusted life-years [QALYs]) and determined incremental cost-effectiveness ratios (ICERs) over a 50-year analytic horizon. We assessed vaccination of 14-year-old girls and catch-up vaccination for 15–24-year-old women in the context of an existing chlamydia screening program and assumed 2 prevaccination prevalences of 3.2% by main analysis and 3.7% by additional analysis. Estimated ICERs of vaccinating 14-year-old girls were $35,300/QALY by main analysis and $16,200/QALY by additional analysis compared with only screening. Catch-up vaccination for 15–24-year-old women resulted in estimated ICERs of $53,200/QALY by main analysis and $26,300/QALY by additional analysis. The ICER was most sensitive to prevaccination prevalence for women, followed by cost of vaccination, duration of vaccine-conferred immunity, and vaccine efficacy. Our results suggest that a successful chlamydia vaccine could be cost-effective.     

Determinant factors of the difference between self-reported weight and measured weight among Japanese

Objectives

To assess the difference between self-reported and measured weight values in Japanese men and women and to determine the underlying determinants of the differences between self-reported and measured values.

Methods

The data were collected from 363 general Japanese individuals aged 16–88 years living in Kumamoto prefecture. Participants completed a self-administered questionnaire designed for this study with self-reported weight and height values. Measured weight and height were measured immediately after questionnaire completion. Paired t-tests identified differences between self-reported and measured values by sex. Multiple-stepwise regression analysis examined the independent variables’ effects on the differences between self-reported and measured weights.

Results

Significant differences were found between self-reported and measured values for both sexes (p < 0.001). There was a significant negative relationship between the difference in an individual’s self-reported and measured weight in each sex, with higher measured weight individuals more likely to underestimate their weight. Multiple-stepwise regression analysis models explained 12.1 % (p < 0.01), 11.3 % (p < 0.01), and 5.6 % (p < 0.01) of the variance in all participants, men, and women, respectively. Significant effects were found for age, weight measurement frequency, and measured weight in total participants, weight measurement frequency, and measured weight for men, and age for women.

Conclusions

In this study, the mean absolute value of the weight and height variances proved the unreliability of self-reported weight and height values. This study’s findings suggest self-reported weight inaccuracy especially for obese populations. This should be adjusted when using it in epidemiological studies and healthcare planning.

     

延安市学龄儿童体格发育现状及相关因素分析

目的了解延安市学龄儿童体格发育现状,并分析相关因素,为促进当地儿童体格发育提供基础资料。方法整群抽样延安市城区和郊区各3所小学,被抽取小学所有儿童参加调查,测量儿童身高、体重,同时采用问卷,调查儿童睡眠、运动、饮食等情况,按照性别、年龄、区域分析身高、体重特点,并与2005年中国九市儿童体格调查数据进行比较,分析影响当地学龄儿童体格发育的可能因素。结果 1)延安市学龄儿童身高与2005年中国九市儿童体格标准比较,无论城区还是郊区,身高普遍低于九市标准(P0.05),且随年龄增大差距有增大趋势,郊区儿童身高表现更明显。2)体重与九市儿童标准比较,12岁之前差异不明显,12岁之后,城区男女生、郊区女生与九市儿童差距逐渐增大(P0.05)。3)控制母亲身高、儿童性别等遗传因素后,补充鱼肝油、喝奶、晚上10点之前睡觉、经常运动等因素可促进延安市学龄儿童体格发育。结论延安市学龄儿童体格发育较全国平均水平落后,且随着年龄的增长差距逐渐增大,积极改善营养、加强运动或可提高学龄儿童体格发育水平。     

注意力缺陷多动障碍患儿的骨龄发育水平和体质量的研究

目的探讨注意力缺陷多动障碍(attention deficit hyperactivity disorder,ADHD)儿童的骨龄发育水平与体质指数(body mass index,BMI),为ADHD开展有效的治疗与预防措施提供依据。方法采取自愿原则选自本院保健科心理门诊6~11岁的符合美国精神障碍诊断统计手册(DSM-Ⅳ)诊断标准的初诊ADHD儿童53例为观察组,生长发育门诊中选取正常健康儿童53例为对照组,采用数字化摄影仪拍摄左手腕骨正位X线片,用统一标准测量身高、体重,按CHN法(中国人手腕部骨发育评价标准)骨龄标准评价手腕骨龄片。结果观察组身高年龄与实际年龄的差均值(0.8±1.1)与对照组(-0.1±0.6)的比较差异有统计学意义(P0.001),骨龄与实际年龄差均值与对照组比较差异有高度统计学意义(P0.001),遗传身高与预测终身高的差均值(1.1±1.0)与对照组(1.0±0.4)比较差异无统计学意义(P0.05),BMI观察组(18.1±3.5)与对照组(16.2±2.3)两组均值比较差异有统计学意义(P0.05)。结论 ADHD儿童的骨龄发育水平较早,体质指数偏高,不影响成年身高。     

Seasonal variations of in vivo and in vitro melatonin production in a passeriform bird, the house sparrow (Passer domesticus)

Melatonin, released from the pineal gland, is an important signal within the circadian pacemaking system of passeriform birds. Until now, seasonal variations in melatonin production have only been examined in a few avian species and the role of melatonin in the regulation of annual rhythms in birds is unclear. We investigated plasma melatonin in a group of house sparrows kept in an outside aviary in spring (March/April), summer (May/June), autumn (September/October), and winter (December/January). The durations of elevated melatonin values mirrored the seasonal changes in night length to a certain degree, the melatonin signal being longest in winter and shortest in summer. Additionally, plasma melatonin peak amplitudes differed significantly among seasons, with highest values in spring and summer and lowest values in winter. Cultured explanted pineal glands obtained from animals in winter and summer showed patterns of in vitro melatonin release comparable to in vivo circulating melatonin with different durations of elevated melatonin and peak amplitude values. These data indicate that the circadian pacemaking system of the house sparrow changes properties seasonally, either as a result of endogenous mechanisms or in response to environmental conditions. These properties are maintained in the pineal gland even after isolation from the animal.     

Osteoporosis in children and young adults

Osteoporosis is a major public health problem with serious long-term complications. In children, the definition of osteoporosis is not only based on densitometric criteria but also takes into account vertebral and long bone fragility fractures. Several factors, such as long-term high-dose steroids, chronic inflammation, malnutrition, immobility, lack of sex steroids, and medication can reduce bone density and increase the risk for fragility fractures when left untreated. Also, genetic conditions can predispose to primary bone fragility disorders, with osteogenesis imperfecta being the most common. Furthermore, since the growing skeleton is at an increased rate of bone remodeling, the ability to heal long bone fractures and reshape vertebral fractures differentiates children from adults. The scope of this chapter is to review the risk factors of osteoporosis and fragility fractures and describe the commonest causes of primary and secondary osteoporosis and their management in children and young adults.     

Secular trends of height,weight and BMI in young adult Brazilian military students in the 20th century

Abstract

Background: Secular trends of increasing weight and height over past centuries are well documented in developed countries. However, these data are still scarce in developing countries such as Brazil.

Aim: To verify the secular trends of height, weight and body mass index (BMI) of military students from Brazilian Army schools who were born between the 1920s and 1990s.

Sample and methods: A retrospective study was performed, which included a survey of data from the files of two Army schools. The sample was composed of subjects aged between 18–20 years old.

Results: The study analysed 2169 heights and 1741 weights and BMIs. During the evaluation period, height increased 7.3?cm, weight 9.8?kg and BMI 1.8?kg/m². The most significant gains were observed in subjects born from the 1920s to the 1940s and the 1960s to the 1970s.

Conclusion: Secular trends of growth in military students born in the 20th century were positive in Brazil, although increases were not constant decade-by-decade.     

Models for cultural inheritance: a general linear model

Background: Body mass index (BMI) is often criticised since it doesn’t consider sex, age and ethnicity, which may affect the height scaling exponent of the equation.

Aims: First, to identify specific height scaling exponents (α) based on sex, age and ethnicity. Second, to assess the performance of the current vs the proposed BMI equations (1) to predict total fat mass (TFM) and metabolic syndrome (MetS) severity and (2) to correctly identify obese individuals and those having MetS.

Methods: In total, 41,403 individuals aged 20–80?years (NHANES, 1999–2014) were studied. Specific “α” were identified using the Benn formula. Various statistical approaches were performed to assess performances of the current vs the proposed-BMIs.

Results: The proposed “α” varies from 1.2 to 2.5, after considering sex, age and ethnicity. BMIs calculated using the proposed “α” showed a similar capacity to predict TFM and MetS severity and to correctly identify obese individuals and those having MetS compared to the current BMI.

Conclusions: Despite sex, age and ethnicity modulating the height scaling exponent of the BMI equation, using these proposed exponents in the BMI equation didn’t improve the capacity to predict TFM and MetS severity, suggesting that the current BMI remains a valid clinical tool.