In theory, the highest level of evidence comes from meta-analysis of randomised clinical trials. In meta-analyses of observational studies, their quality depends on the quality of the included studies. In the present case, the large number of included studies (357) increases the potential heterogeneity among studies but, on the other hand, may minimise and dilute the possible bias of individual studies. The large number of included studies and their calculation with a 95 % confidence interval make the data very reliable, probably the most reliable data currently available on the occurrence of headache, migraine and tension-type headache in the world. 

Global burden of disease studies, regularly published in the Lancet, already established that tension-type headache and migraine were the second and third most prevalent diseases in the world, including all causes of disease and not just neurological ones. This new paper puts this information into context, noting that these are extremely common diseases, regardless of the territory studied. 

To assess the frequency of a disease, it can be studied in different ways: through individual patient interviews conducted by healthcare professionals, through interviews conducted by non-healthcare evaluators, through telephone surveys, through questionnaires, etc. In this paper, the figures are compared according to the methodology of the studies, but the differences are not particularly striking. 

The authors of the study are the coordinators of the Lifting the Burden campaign, which aims to visualise the impact of headache worldwide. They have put a great deal of effort into developing standardised and comparable tools to assess the frequency of headache worldwide and its impact. 

Two out of three people will experience headache in their lifetime, and one in two will have experienced headache in the last year. Both migraine and tension-type headache are more common in women. Approximately 4.5 % of the population has more days with pain than without pain in a month.

Headaches are very disabling diseases but there are effective treatments available that reduce the disability caused by them and allow patients to lead a normal life.

Analyses such as this one show again that migraine and the other primary headaches have a very high prevalence in the population (up to 52% headache and 14% migraine) globally (1 billion worldwide), with a daily incidence of 15.8% of migraine attacks per day. That is about 86 million migraine attacks per day. 

In addition to being high, the prevalence of migraine has been increasing in recent years, and it is now the most prevalent and disabling neurological disease between adolescence and age 50.

However, research in this field is underfunded, so why do we want to live many years if they are not of good quality? As a society we have to consider not only the quantity of life, but also the quality of life, and addressing the issue of improving quality of life in mid-life means researching, treating and providing access to treatment for migraine sufferers.