There are estimated to be around 56m deaths per year according to the World Health Organisation - and it's thought half are not registered - so there is a lot of missing information about what people die of. The Million Deaths Study aims to change that by investigating one million deaths in India - and there have been some surprising discoveries.
In a small house near Bangalore, the loud hum of silk spinning machines in the background, Maniamma relates the details of her husband's death a few months ago.
"The day he died he went to see our daughter who lives in a nearby village. While returning, he had some problems - perhaps a minor heart attack. He got out of the car but couldn't walk."
He died at 6am the following morning.
All the details are recorded by Ashok Kumar, a trained fieldworker, who is carrying out a "verbal post mortem", a technique often used to record causes of death in developing countries.
It's part of a huge study surveying and analysing one million deaths in India.
Hospital deaths 'exception'
Knowing what is killing people is vital - it helps save lives by ensuring public health money is spent on the right things. In the developed world almost all deaths are registered and the cause of death recorded on an official medical death certificate.
By contrast, most deaths in the developing world go unrecorded, and estimates of the causes of death are generally based on people who die in hospitals and under medical supervision.
But hospital deaths are the exception in India.
"India has about nine million deaths [a year], most of which occur at home and in rural areas" - says Prof Prabhat Jha, who leads the study from the Centre for Global Health Research in Toronto.
The Million Deaths Study (MDS) uses "verbal autopsies" or post-mortems - interviewing those close to the deceased about what happened before their death - as a way of addressing this gap.
The million deaths are chosen from a representative sample of areas across India, and the aim is to ascertain the cause of death in each one.
It's a mammoth task - 60,000 homes per year have been visited over the course of 14 years and they are set to reach the millionth death later this year.