Life Expectancy & Mortality Rates

What's The Difference Between Life Expectancy and Mortality Rates?

It occurred to me yesterday while I was reading The Blue Zones that there is a difference between life expectancy and mortality and many people might not see the difference at first glance. I thought that a description of the two concepts would be a welcome addition to this blog and a good reference point for the many posts that touch on these two ideas.

What Is Life Expectancy?

Basically an average age that one might expect for a person to live to based on a starting point in time is Life Expectancy. Often this point is birth but in the breakdown of demographics the basis can be any age that you like. Making the basis age higher than birth removes many anomalies from the statistics such as infant deaths and early deaths due to various developmental problems or accidents.

Basing life expectancy off the age of 20 years for instance will show that the average 20 year old person will life to X years of age. This number will be higher than the average life expectancy of someone from birth because we are purposefully removing the early deaths from the calculation. Furthermore a average life expectancy of 60 year old people will be even higher because we are removing even more early deaths from he calculation. If you make it to 60 then you are statistically more likely to make it to 90 than a newborn is.

Additionally you can also look at life expectancy from the perspective of when someone was born. The average birth in 1900 for instance had a life expectancy far shorter than a birth in the year 2000. Due to medical advances we can safely say that newborns will live longer lives today than they did generations ago. Expanding on the concept of medical advances however, we can also assume that all people will benefit from medical advances thus, someone born in 1949 who is 60 years old might have had a certain life expectancy at their birth of 'X' years of age but through medical advances during his or her lifetimes the life expectancy of this person has increased. Less people would have made it to the age of 60 but of those who have made it to 60 they will more likely live longer because of new medicine.

Because life expectancy can be broken down to such small segments it becomes increasingly difficult to put blanket statements on all people. New medicine might save more premature babies from dying but this does nothing to change the life expectancy rate of those born in 1949. Those born in 2009 however will likely see an increase to their life expectancies because less babies will die in their first weeks of life. This however does nothing to change the mortality rate of the baby born in 2009 once they reach the age of 1. By the time 2010 rolls around and the 2009 babies are now 1 years old their average life expectancy might be higher but their mortality rate is unchanged. They are just as likely to die from other causes as anyone else who did not benefit from the medical advances their demographic group benefited from. This leads us to Mortality rates.

What are Mortality Rates?

The statistical likelihood that you’ll live 'X' amount of time beyond a certain point is a mortality rate. From birth you are very likely to live to your first year. You are less likely to make it to 50 and you are even less likely to live to one hundred. However, a 90 year old is statistically far more likely to reach one hundred than a baby is because they have avoided death for ninety years already.

To go back to the example above regarding babies and advances in preventing newborn death, a newborn born before the advances, will have a mortality rate of surviving the first month that is lower than a baby who was born after the advances in technology, but the newborns who do make it past the first month from either group now have the same mortality rates to live to 90 years old because everything else is equal from here on out.

Despite this however, their will be more 90 year olds left from the group that was born after the advances because less of them died in the first month of life. This absolute number of 1 month olds will be larger than the 1 month olds who were born before this hypothetical medical advance thus, if 10 percent of them make it to 90 years of age their will be more of them because a percentage of a higher basis yields a larger result. The same holds true for older people.

If a sixty year old has access to new blood pressure medication their mortality rate will decrease and they will be more likely to live to 90 years old. Life expectancy for this person will increase but the sheer magnitude of 90 years olds thirty years from now will not be that great because the basis for this increase in life expectancy includes only those people who didn’t die before age 60. There is less people to apply the new mortality rate to and thus the absolute number of 90 year olds 30 years from now will be higher but not as much so if the medication was available when these people were 40 rather than 60, or 20 rather than 60.

Bringing It All Together

All this could be further broken down and explained into painful detail but the point being is that life expectancy is the average age that one might be expected to live to based on certain data points. Mortality rate is the chances that they will die in a given time period or of a certain cause.

Because everyone has a 100 percent mortality rate in the long run, this measure needs a qualification point to be meaningful, such as the mortality rate of a coronary bypass patient over the course of 30 days, 90 days, five years, or the mortality rate of healthy teens living to 90 years of age, or the mortality rate of hospice patients in Vermont living an additional 1 year, or the mortality rates of quitting smoking and living to 80 years of age. No matter the situation the mortality rate is related to the life expectancy but is fundamentally different.