4.12: Reporting Births, Deaths, Diagnoses

Here's a typical headline you might see: "Colon Cancer Deaths Rise Among Younger Adults, and No One Knows Why." Did you ever wonder where journalists get statistics like that?

They usually get them from public health sources.

To notice sharp changes in mortality (like this news story about colon cancer), we have to keep track of what people die of. To compare different populations over time, we need to be systematic about tracking statistics in the same way across the country, and for some health statistics, across the world.

This is common sense -- if you want to know how much money you spend, you have to write it down, and if you want to know if you are able to do more pushups in November than you can in April, you have to write it down and look at the data-- and putting it into systems that can be used everywhere. So, health departments across the US report on all births and deaths (called "vital statistics") and on rates of disease.

In the case of certain infectious diseases, especially those that could become epidemic, they are called notifiable diseases because health departments must notify the Centers for Disease Control and Prevention (CDC) on new cases identified each week. The causes of death are reported on death certificates, which allows us to track mortality rates from a wide array of causes (not just infectious diseases).

Standardized Measurements of Health Status of Populations

When you go to see a doctor, they probably take your blood pressure and temperature every time you have an appointment. These are quick indicators of a person's health. Similarly, when we look at a population's health, there are some measurements that we check every time, as they are good indicators of overall health of the population.

Three of the most important categories of population health measures are mortality statistics, life expectancy and years of potential life lost.

• Mortality statistics (death statistics) are the most reliable measure of a population's health. You will see next week, when we look at health inequalities, that mortality statistics are a key measure used when comparing the health of different populations.
• Life expectancy is the average number of years a person from a specific cohort is projected to live from a given point in time. Most commonly you will see life expectancy from birth -- that is, for a person born today, how many years can they be expected to live? Sometimes you will see life expectancy reported from another age. For example, retirement planners might want to know, if a person makes it to age 65, how much longer can they expect to live?There are large differences in life expectancy among different populations in the US (men vs. women, different races, different educational levels). There are even greater differences (inequalities) between life expectancy in poor countries and rich countries around the world.

I mentioned that life expectancy changes over time. It is a key thing that public health professionals keep their eye on. The Swedish statistician Hans Rosling has made some beautiful and entertaining graphics to talk about global public health improving over time, using life expectancy as the indicator. Optional: Take a moment to explore the data on Hans Rosling's Gapminder website, which enables you to try out different types of charts to answer your own questions.

• Years of potential life lost (YPLL) is a measure of how many people are dying young from a certain cause. It is calculated by subtracting a person's age at death from a standard age, usually 75. If you looked at 1000 deaths from childhood cancers, for example, the YPLL would be much higher than if you considered 1000 deaths from lung disease, which usually occurs later in life.

However, if you look at a disease that is very common like heart disease (the leading cause of death in the US), even if it mostly kills older people, the total YPLL is much higher than a less-common cause of death like homicide, simply because more people are affected.

Other measures of population health

There are other measures that seek to assess not only years of life, but something about quality of life, including disability-adjusted life years and health-adjusted life expectancy. These measures, discussed in your textbook, are commonly used in public health. Some see them as problematic or inadequate measures, as they seem to equate disability with not living at all, or living less. Many people who live with disabilities argue with this. Yet sometimes there can be value to using these measures (DALY and HALE), especially when modern medicine falls into the trap of extending years of life without attention to quality of life. Keep in mind that many people living with disabilities have a high quality of life, and that many barriers to a high quality life are about opportunity and social conditions, not physical health.

Here is an optional short video that does a nice job of explaining YPLL:

Years of Potential Life Lost video