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Preview: American Journal of Epidemiology - current issue

American Journal of Epidemiology Current Issue

Published: Wed, 23 Aug 2017 00:00:00 GMT

Last Build Date: Fri, 15 Sep 2017 02:47:15 GMT




The Harm Done to Reproducibility by the Culture of Null Hypothesis Significance Testing


In the last few years, stakeholders in the scientific community have raised alarms about a perceived lack of reproducibility of scientific results. In reaction, guidelines for journals have been promulgated and grant applicants have been asked to address the rigor and reproducibility of their proposed projects. Neither solution addresses a primary culprit, which is the culture of null hypothesis significance testing that dominates statistical analysis and inference. In an innovative research enterprise, selection of results for further evaluation based on null hypothesis significance testing is doomed to yield a low proportion of reproducible results and a high proportion of effects that are initially overestimated. In addition, the culture of null hypothesis significance testing discourages quantitative adjustments to account for systematic errors and quantitative incorporation of prior information. These strategies would otherwise improve reproducibility and have not been previously proposed in the widely cited literature on this topic. Without discarding the culture of null hypothesis significance testing and implementing these alternative methods for statistical analysis and inference, all other strategies for improving reproducibility will yield marginal gains at best.

Invited Commentary: Can Issues With Reproducibility in Science Be Blamed on Hypothesis Testing?


In the accompanying article (Am J Epidemiol. 2017;186(6):646–647), Dr. Timothy Lash makes a forceful case that the problems with reproducibility in science stem from our “culture” of null hypothesis significance testing. He notes that when attention is selectively given to statistically significant findings, the estimated effects will be systematically biased away from the null. Here I revisit the recent history of genetic epidemiology and argue for retaining statistical testing as an important part of the tool kit. Particularly when many factors are considered in an agnostic way, in what Lash calls “innovative” research, investigators need a selection strategy to identify which findings are most likely to be genuine, and hence worthy of further study.

Invited Commentary: The Need for Cognitive Science in Methodology


There is no complete solution for the problem of abuse of statistics, but methodological training needs to cover cognitive biases and other psychosocial factors affecting inferences. The present paper discusses 3 common cognitive distortions: 1) dichotomania, the compulsion to perceive quantities as dichotomous even when dichotomization is unnecessary and misleading, as in inferences based on whether a P value is “statistically significant”; 2) nullism, the tendency to privilege the hypothesis of no difference or no effect when there is no scientific basis for doing so, as when testing only the null hypothesis; and 3) statistical reification, treating hypothetical data distributions and statistical models as if they reflect known physical laws rather than speculative assumptions for thought experiments. As commonly misused, null-hypothesis significance testing combines these cognitive problems to produce highly distorted interpretation and reporting of study results. Interval estimation has so far proven to be an inadequate solution because it involves dichotomization, an avenue for nullism. Sensitivity and bias analyses have been proposed to address reproducibility problems (Am J Epidemiol. 2017;186(6):646–647); these methods can indeed address reification, but they can also introduce new distortions via misleading specifications for bias parameters. P values can be reframed to lessen distortions by presenting them without reference to a cutoff, providing them for relevant alternatives to the null, and recognizing their dependence on all assumptions used in their computation; they nonetheless require rescaling for measuring evidence. I conclude that methodological development and training should go beyond coverage of mechanistic biases (e.g., confounding, selection bias, measurement error) to cover distortions of conclusions produced by statistical methods and psychosocial forces.

Comparison of Health Examination Survey Methods in Brazil, Chile, Colombia, Mexico, England, Scotland, and the United States


Comparability of population surveys across countries is key to appraising trends in population health. Achieving this requires deep understanding of the methods used in these surveys to examine the extent to which the measurements are comparable. In this study, we obtained detailed protocols of 8 nationally representative surveys from 2007–2013 from Brazil, Chile, Colombia, Mexico, the United Kingdom (England and Scotland), and the United States—countries that that differ in economic and inequity indicators. Data were collected on sampling frame, sample selection procedures, recruitment, data collection methods, content of interview and examination modules, and measurement protocols. We also assessed their adherence to the World Health Organization's “STEPwise Approach to Surveillance” framework for population health surveys. The surveys, which included half a million participants, were highly comparable on sampling methodology, survey questions, and anthropometric measurements. Heterogeneity was found for physical activity questionnaires and biological samples collection. The common age range included by the surveys was adults aged 18–64 years. The methods used in these surveys were similar enough to enable comparative analyses of the data across the 7 countries. This comparability is crucial in assessing and comparing national and subgroup population health, and to assisting the transfer of research and policy knowledge across countries.

Hormone Therapy Use and Risk of Chronic Disease in the Nurses’ Health Study: A Comparative Analysis With the Women's Health Initiative


Observational studies and randomized controlled trials of menopausal hormone therapy (HT) and chronic disease risk appear to have divergent results for cardiovascular disease. However, differences may be related to a modifying effect of age, time since menopause, and HT formulation. In the Nurses’ Health Study (NHS) (enrolling during 1980–1994 and following participants until 2002), we investigated associations between the use of oral conjugated equine estrogens (CEE) (0.625 mg/day) plus medroxyprogesterone acetate (MPA) (<10 mg/day) or oral CEE alone and cardiovascular disease, cancer, all-cause mortality, and other major endpoints among postmenopausal women, aged 50–79 years at HT initiation. Among women aged 50–59 years at HT initiation, associations of CEE alone or CEE+MPA with most clinical outcomes were highly concordant between NHS and Women's Health Initiative (WHI). However, for myocardial infarction, results for CEE+MPA were in the direction of risk elevation in WHI and in the direction of risk reduction in NHS. When examined according to years since menopause onset (<10 years) rather than age group, results were nonsignificant and concordant for both studies. Because few women in the NHS initiated HT after age 60 years, we did not examine associations in this group. Discrepancies between NHS and WHI could largely be attributed to differences in the age structure of the populations and age at HT initiation.

Sleep Apnea, Disability Pensions, and Cause-Specific Mortality: A Swedish Nationwide Register Linkage Study


Sleep apnea is a common problem affecting daily functioning and health. We evaluated associations between sleep apnea and receipt of a disability pension and mortality in a prospective study of 74,543 cases of sleep apnea (60,125 outpatient, 14,418 inpatient) from the Swedish Patient Register (2000–2009 inclusive). Cases were matched to 5 noncases (n = 371,592) and followed from diagnosis/inclusion to December 31, 2010, via nationwide registers. During a mean follow-up period of 5.1 (standard deviation, 2.7) years, 13% of men and 21% of women with inpatient sleep apnea received a disability pension. Inpatient sleep apnea was associated with higher total mortality (for men, hazard ratio (HR) = 1.71, 95% confidence interval (CI): 1.59, 1.84; for women, HR = 2.33, 95% CI: 2.04, 2.67), with associations being strongest for deaths due to ischemic heart disease (for men, HR = 2.27, 95% CI: 1.94, 2.65; for women, HR = 5.27, 95% CI: 3.78, 7.34), respiratory disorders (for men, HR = 3.29, 95% CI: 2.45, 4.42; for women, HR= 5.24, 95% CI: 3.52, 7.81), and suicide (for men, HR = 1.76, 95% CI: 1.19, 2.60; for women, HR = 4.33, 95% CI: 1.96, 9.56). There were no associations of inpatient sleep apnea with cancer mortality. Outpatient sleep apnea was associated with a higher risk of receiving a disability pension but not higher total mortality. In conclusion, inpatient sleep apnea is related to a higher risk of disability pension receipt and mortality a decade after diagnosis.

Who Among the Elderly Is Most Vulnerable to Exposure to and Health Risks of Fine Particulate Matter From Wildfire Smoke?


Wildfires burn more than 7 million acres in the United States annually, according to the US Forest Service. Little is known about which subpopulations are more vulnerable to health risks from wildfire smoke, including those associated with fine particulate matter. We estimated exposure to fine particles specifically from wildfires, as well as the associations between the presence of wildfire-specific fine particles and the amount of hospital admissions for respiratory causes among subpopulations older than 65 years of age in the western United States (2004–2009). Compared with other populations, higher fractions of persons who were black, lived in urban counties, and lived in California were exposed to more than 1 smoke wave (high-pollution episodes from wildfire smoke). The risks of respiratory admissions on smoke-wave days compared with non–smoke-wave days increased 10.4% (95% confidence interval: 1.9, 19.6) for women and 21.7% (95% confidence interval: 0.4, 47.3) for blacks. Our findings suggest that increased risks of respiratory admissions from wildfire smoke was significantly higher for women than for men (10.4% vs. 3.7%), blacks than whites (21.7% vs. 6.9%), and, although associations were not statistically different, people in lower-education counties than higher-educated counties (12.7% vs. 6.1%). Our study raised important environmental justice issues that can inform public health programs and wildfire management. As climate change increases the frequency and intensity of wildfires, evidence on vulnerable subpopulations can inform disaster preparedness and the understanding of climate change consequences.

Apolipoprotein C-III and High-Density Lipoprotein Subspecies Defined by Apolipoprotein C-III in Relation to Diabetes Risk


Apolipoprotein C-III (apoC-III) is a potentially novel biomarker that may play an important role in the pathogenesis of diabetes, particularly when present on the surface of high-density lipoprotein (HDL). In a case-cohort study carried out among 434 incident diabetes cases occurring before 2007 and 3,101 noncases in the Danish Diet, Cancer, and Health Study, we examined associations of baseline (1993–1997) plasma concentrations of apoC-III and subspecies of HDL defined by the presence or absence of apoC-III with risk of diabetes using Cox regression. ApoC-III was strongly associated with risk of diabetes (for top quintile vs. bottom quintile, hazard ratio (HR) = 3.43, 95% confidence interval (CI): 1.75, 6.70; P-trend < 0.001). The cholesterol concentration of HDL (HDL cholesterol (HDL-C)) without apoC-III was inversely associated with risk of diabetes (HR = 0.48, 95% CI: 0.27, 0.85; P-trend = 0.002), more so than total HDL-C (HR = 0.60, 95% CI: 0.35, 1.03; P-trend = 0.04), whereas HDL-C with apoC-III was not associated (HR = 1.05, 95% CI: 0.50, 2.21; P-trend = 0.44) (for HDL-C with apoC-III vs. HDL-C without apoC-III, P-heterogeneity = 0.002). ApoC-III itself is a strong risk marker for diabetes, and its presence on HDL may impair the antidiabetogenic properties of HDL. ApoC-III has potential to be a therapeutic target for the prevention of diabetes.

Maternal Exposure to Nitrogen Dioxide, Intake of Methyl Nutrients, and Congenital Heart Defects in Offspring


Nutrients that regulate methylation processes may modify susceptibility to the effects of air pollutants. Data from the National Birth Defects Prevention Study (United States, 1997–2006) were used to estimate associations between maternal exposure to nitrogen dioxide (NO2), dietary intake of methyl nutrients, and the odds of congenital heart defects in offspring. NO2 concentrations, a marker of traffic-related air pollution, averaged across postconception weeks 2–8, were assigned to 6,160 nondiabetic mothers of cases and controls using inverse distance-squared weighting of air monitors within 50 km of maternal residences. Intakes of choline, folate, methionine, and vitamins B6 and B12 were assessed using a food frequency questionnaire. Hierarchical regression models, which accounted for similarities across defects, were constructed, and relative excess risks due to interaction were calculated. Relative to women with the lowest NO2 exposure and high methionine intake, women with the highest NO2 exposure and lowest methionine intake had the greatest odds of offspring with a perimembranous ventricular septal defect (odds ratio = 3.23, 95% confidence interval: 1.74, 6.01; relative excess risk due to interaction = 2.15, 95% confidence interval: 0.39, 3.92). Considerable departure from additivity was not observed for other defects. These results provide modest evidence of interaction between nutrition and NO2 exposure during pregnancy.

Trends in the Relationship Between Obesity and Disability, 1988–2012


Rising obesity rates, coupled with population aging, have elicited serious concern over the impact of obesity on disability in later life. Prior work showed a significant increase in the association between obesity and disability from 1988 to 2004, calling attention to disability as a cost of longer lifetime exposure to obesity. It is not known whether this trend has continued. We examined functional impairment and impairment in activities of daily living (ADL) (defined as severe or moderate to severe) for adults aged 60 years or older (n = 16,770) over 3 time periods in the National Health and Nutrition Examination Survey. The relative odds of impairment for obese individuals versus normal-weight individuals significantly increased from period 1 (1988–1994) to period 2 (1999–2004) for all outcomes. In period 3 (2005–2012), this association remained stable for functional and severe ADL impairment and decreased for moderate-to-severe ADL impairment. The fraction of population disability attributable to obesity followed a similar trend. The trend of an increasing association between obesity and disability has leveled off in more recent years, and is even improving for some measures. These findings suggest that public health and policy concerns that obesity would continue to become more disabling over time have not been borne out.

Risk Factors Associated With Suicide Completions Among US Enlisted Marines


US enlisted Marines have experienced a substantial increase in suicide rates. We sought to identify risk factors for suicide completions among male Marines who entered basic training in San Diego, California, between June 2001 and October 2010. Suicides that occurred during active-duty military service were counted from June 1, 2001, through June 30, 2012. A total of 108,930 male Marines (66,286 deployers and 42,644 never deployed) were followed for 467,857 person-years of active-duty service time. Of the 790 deaths, 123 (15.6%) were suicides. In the final multivariate hazard model, preservice characteristics of not being a high-school graduate (hazard ratio (HR) = 2.17, 95% confidence interval (CI): 1.28, 3.68) and being a smoker at the time of enlistment (HR = 1.91, 95% CI: 1.32, 2.76) were significantly associated with a higher risk for suicide completion. Diagnosed with traumatic brain injury (HR = 4.09, 95% CI: 2.08, 8.05), diagnosed with depression (HR = 2.36, 95% CI: 1.22, 4.58), and received relationship counseling (HR = 3.71, 95% CI: 1.44, 9.54) during military service were significant risks for suicide death. Deployment alone was not significantly associated with a risk for suicide death (HR = 0.53, 95% CI: 0.26, 1.05).

Time Spent Commuting to Work and Mental Health: Evidence From 13 Waves of an Australian Cohort Study


Time-related stressors, such as long working hours, are recognized as being detrimental to health. We considered whether time spent commuting to work was a risk factor for poor mental health. Data from the Household, Income Labour Dynamics in Australia Survey were used to conduct fixed-effects longitudinal regression analyses. The outcome variable was the Mental Health Inventory, and the main exposure represented hours per week traveling to and from a place of paid employment. Effect modifiers included sex, low job control, high demands, and low job security. Compared with when a person commuted for ≤2 hours per week, there was a small decline (coefficient = −0.33, 95% CI: −0.62, −0.04; P = 0.025) in the Mental Health Inventory score when they commuted for over 6 hours per week. Compared with persons with high job control, persons working in jobs with low job control experienced significantly greater declines in the Mental Health Inventory score when commuting 4 to 6 hours per week and when commuting over 6 hours per week. We found no influence from the other hypothesized effect modifiers. These results suggest the importance of considering commuting time as an additional work-related time stressor.

Associations of Statin Use With Colorectal Cancer Recurrence and Mortality in a Danish Cohort


In earlier studies of the influence of hydroxymethylglutaryl-coenzyme A reductase inhibitors (also known as statins) on colorectal cancer prognosis, investigators reported a reduced rate of cancer-specific mortality. Studies of recurrence are few and small. Using data from Danish registries, we followed 21,152 patients diagnosed with stage I–III colorectal cancer from 2001 to 2011. We estimated the association between statin use in the preceding year and cancer recurrence, cancer-specific mortality, and all-cause mortality rates. We identified 5,036 recurrences, 7,084 deaths from any cause, and 4,066 deaths from colorectal cancer. After adjustment for potential confounders, statin use was not associated with recurrence (adjusted hazard ratio (aHR) = 1.01, 95% confidence interval (CI): 0.93, 1.09), but it was associated with death from colorectal cancer (aHR = 0.72, 95% CI: 0.65, 0.79) and death from any cause (aHR = 0.72, 95% CI: 0.67, 0.76). Statin use in the year preceding recurrence was associated with a reduced risk of cancer-specific mortality (aHR = 0.83, 95% CI: 0.74, 0.92) but also a reduced risk of death from any other cause (aHR = 0.78, 95% CI: 0.61, 1.00). Statin use was not associated with a reduced rate of colorectal cancer recurrence, but it was associated with a reduced rate of cancer-specific mortality, which suggests that there is no cancer-directed benefit; therefore, there is no basis to prescribe statins to colorectal cancer patients who do not have cardiovascular indications.