The Global Burden of Disease Methodology Has Been Good for Mental Disorders: But Not Good Enough

Abstract

The global burden of disease (GBD) studies have revolutionized how we quantitate the burden of disease. Bold in vision, virtuosic in methodology, encyclopedic in scope— the findings have been highly influential. GBD has allowed the health community to combine a measure of premature mortality (years of life lost [YLLs]) with a measure of disability (years lived with disability [YLDs]) in order to derive an overall measure of disease burden (disability adjusted life-years; DALYs). These innovative health metrics have highlighted the increasing contribution of chronic disability to the total burden of disease in the epidemiological transition seen in all countries and territories of the world. Total YLDs are influenced by the years of life lived with a disorder and a disability weight allocated to that disorder. Prevalent disorders with small disability weights may contribute more YLDs to the total compared to rare disorders with large disability weights. Within the common disorders with mild to moderate disability, those with an early onset, and a persistent or recurrent trajectory, will figure prominently in total YLDs. Mental disorders, among others, often have an early onset and thus meet these criteria. If cardiovascular and respiratory disorders are the chronic disorders of the elderly, mental disorders are the chronic disorders of people of all ages—children, adolescents, middle-aged, and old. The contribution of mental disorders to disease burden has been put into sharp focus by the GBD methodology. In the “league table of disorders,” mental disorders make a major contribution to the YLDs associated with noncommunicable disorders and was the Top 2 YLD burden of all diseases in the world in 2017. So, three cheers for the GBD—these methods have been good for mental disorders. Vigo and colleagues have drawn attention to instances where the GBD may underestimate the true contribution of mental disorders to the total disease burden. In the target article, they revisit this topic, with data extracted from the 2017 estimates for Canada, the United States, and Mexico. They provide a convincing case that mental disorders should include the YLDs from intentional self-harm and the YLLs from suicide along with the officially sanctioned mental disorder-associated causes of death (alcohol use disorders, drug use disorders, eating disorders). Furthermore, they argue that mental disorders should harvest YLLs and YLD from selected neurological disorders, which are currently reported separately from mental disorders in GBD. With the redistribution of disorders into the “mental, neurological, substance use disorders and self-harm,” Vigo and colleagues estimated that the burden associated with this revised definition is the largest of all disorder groupings, especially in the United States. Where the boundary should be drawn between neurological and psychiatric disorders is debatable (and influenced more by history and discipline loyalties than by empirical data). However, we agree that GBD’s current methodology systematically underestimates the burden of mental disorders. We wish to advocate for an additional change to the GBD methods that would contribute to a more realistic estimation of the disease burden of mental disorders. The current method links all YLLs to a single death based on a