How much Person-Time is there?

Posted on 06/04/2012

Nobody knows exactly. It depends on how many people there are alive on the planet and which part of the population has records which are accessible in a useful way. At the most basic level these records should document a person’s birth, death, and cause of death.

The most up to date United Nations estimate for the world’s population hit 7 billion in 2011. This means that between all of us we experience as many person-years each year. That is equivalent to over 19 million person years per day, 800,000 person years per hour, 13,000 person years per minute or 220 person years per second. This means that we collectively live through 220 years’ worth of human life, the equivalent of more than four human lifespans every single second. Now. And now. And now again. This is the potential amount of person-time we have at our disposal. The problem is that only a very small part of this person time is recorded in a way that is useful for epidemiology and medical research.

How much person-time do we roughly record, and how much do we waste? Again, it’s hard to tell precisely, but a recent WHO estimate tells us that 40 million, or approximately one third of births are not registered each year. Beside the huge practical and legal problems faced by people whose existence is not registered, the person-time experienced by these people is wasted, as it is not accessible for research.