Overadjustment – an important bias hiding in plain sight

Anita van Zwieten, Fiona M Blyth, Germaine Wong and Saman Khalatbari-Soltani

Epidemiologists are generally well equipped to design and conduct studies that minimise various types of bias, so as to obtain the most accurate estimates possible and therefore high-quality evidence. In observational studies, some types of bias, like confounding, have received a lot of attention, while others have been overlooked. One that has been neglected is overadjustment bias, which occurs when researchers adjust for an explanatory variable on the causal pathway from exposure to outcome when seeking to estimate the total effect.

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Proposing a new indicator to assess health disparities: measuring inequalities in causes of death

Iñaki Permanyer and Júlia Almeida Calazans

Policymakers and scholars are increasingly interested in monitoring and curbing health inequalities. Much is known about the main causes of death and how mortality has been shifting from most deaths around the world being caused by communicable diseases towards most being due to non-communicable causes.

However, less is known about the heterogeneity in these causes of death. Are people in some countries dying from an increasingly varied set of causes? Measuring how ‘similar’ or ‘dissimilar’ the different causes of death are can help us understand global health inequalities and patterns of mortality.

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Why we need a new measure of maternal health: the “lifetime risk of maternal near miss”

Ursula Gazeley

According to the most recent data from the World Health Organization, the lifetime risk of maternal death for a girl in Chad is a staggering 1 in 15, compared with 1 in 43,000 in Norway. This means that a girl in Chad has an almost 3000 times greater risk of dying from a maternal cause during her reproductive lifetime than a girl in Norway. The lifetime risk of maternal death is a useful measure to help us understand this global inequality in maternal mortality.

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Have smartphones and ubiquitous internet access affected sedentary time among children and adolescents?

Jakob Tarp, Knut Eirik Dalene and Ulf Ekelund

As will be obvious to anyone on a bus or train or waiting for coffee, access to screen-based media has been revolutionised over the past two decades. In 2020, there were more than six billion smartphone users worldwide and almost global penetration. Yet, our understanding of how these devices have affected other behaviour, such as sedentary time, is limited.

In our study, recently published in the IJE, we used accelerometer measurements of sedentary time collected for the Norway-wide physical activity monitoring system to estimate that a 9-year-old boy or 15-year-old girl or boy spent, on average, 20 to 30 minutes more each day being sedentary in 2018 than in 2005. We also found that children and adolescents accumulate more of their sedentary time in longer uninterrupted periods, compared with a more fragmented pattern of activity in 2005. Children and adolescents now spend less time sitting for short periods of 5 minutes or less at a time.

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Regular exercise, even in polluted areas, can lower risk of cancer mortality

Yacong Bo and Xiang Qian Lao

Regular exercise is recognised as providing significant lifestyle-related protection against non-communicable diseases. It can also reduce the likelihood of cardiovascular disease, cancer and premature death. By contrast, long-term exposure to fine particulate matter (PM2.5) can increase the likelihood of respiratory and cardiovascular disease and certain cancers, leading to premature death.

Outdoor exercise might increase the inhalation and deposition of air pollutants, potentially counteracting its beneficial effects. Evaluation of this risk–benefit relationship has become an important public health concern because more than 91% of the global population lives in areas where air quality fails to meet the 2005 World Health Organization guidelines.

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Could biomass fuel use perpetuate the poverty trap through cardiovascular disease and all-cause mortality?

Shuyi Qiu and John S Ji

Many people around the world are still using biomass as a fuel for cooking and heating. Inefficient combustion of solid fuels is the primary cause of indoor household air pollution, estimated to be responsible for 4.3 million premature deaths in 2012 (7.7% of total mortality).

The World Health Organization’s latest global air quality guidelines point out that indoor air pollution causes a health burden that mostly affects people in low- and middle-income countries. Many global development agencies are working with governments of developing countries to reduce household air pollution. For example, China’s Relocation Program in the poorest provinces is a significant part of China’s poverty eradication plans. This large-scale program relocates millions of residents in absolute poverty to places with better living conditions, including fuel type.

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How has cardiovascular disease contributed to the rural–urban life expectancy gap?

Leah Abrams

In the United States, rural residents do not live as long as their urban counterparts. This disparity has been widening for decades. Around 1970, urban life expectancy was 70.9 years, compared with 70.5 in rural areas, but by 2005–2009, the difference was greater (78.8 versus 76.8 years). In our research recently published in the IJE, we found that the gap in life expectancy would be even wider today if declines in cardiovascular disease (CVD) mortality had not dramatically slowed around 2010.

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The “double jeopardy” lifestyle effect

How individual and neighbourhood socioeconomic disadvantages jointly affect health-related behaviour

Yinjie Zhu

In our study recently published in the IJE, we found that socioeconomically disadvantaged individuals were more likely to have worse health-related lifestyle behaviour than their neighbours, even if they lived in neighbourhoods with little overall socioeconomic disadvantage.

We also observed a “double jeopardy” effect: an unhealthier lifestyle was found among people with greater individual disadvantage residing in disadvantaged neighbourhoods.

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Higher risk of autism spectrum disorder in children whose parents were born preterm or with low birthweight

Jingyuan Xiao, Zeyan Liew and Jiong Li

Autism spectrum disorder (ASD) comprises a heterogeneous group of impaired neurodevelopmental conditions. The aetiology of ASD is complex and largely unclear, with some recent evidence suggesting the possibility of transmission of risk across multiple generations.

Our study, recently published in the International Journal of Epidemiology, evaluated the associations between birth characteristics of parents and the subsequent risk of ASD in their children.

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Profound impact of smoking, alcohol and obesity on improvements in life expectancy

Fanny Janssen, Sergi Trias-Llimós and Anton Kunst

Smoking, alcohol misuse and behaviours that result in obesity (such as an unhealthy diet and insufficient physical activity) have strong negative effects on individual health. Because these health behaviours are very common among people in Europe, smoking, alcohol and obesity also largely influence mortality rates and life expectancy in Europe.

However, the impact of these three lifestyle factors on life expectancy is likely changing over time. Smoking, obesity and alcohol misuse, like true epidemics, tend to first become more common in a population, followed (eventually) by a decline in their prevalence and associated mortality.

This raises the question of how changes in smoking, obesity and alcohol use have influenced improvements in life expectancy over time. Answering this question is particularly relevant because of the recently observed stagnation in life expectancy improvements in some European countries.

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