Chapter 4- Mortality and Other Measures of Disease Impact

Question 1

Mortality rate

Answer 1

Annual death rate. The total deaths divided by the number of people in the population. If you are interested in the mortality rate of a certain age group or another demographic, you divide the number of deaths for that demographic by the total number of people IN THAT DEMOGRAPHIC. You can also calculate the disease specific mortality rate

Question 2

Case fatality

Answer 2

Determines what percentage of people who have a certain disease die within a certain time after their disease was diagnosed. It is a measure of the severity of the disease. It can also be used to measure any benefits of a new therapy, as therapy improves, case fatality would be expected to decline

Question 3

What is the difference between case fatality and a mortality rate?

Answer 3

In a mortality rate, the denominator represents the entire population at risk of dying from the disease, including both those who have the disease and those who do not have the disease (but who are at risk of developing it). However, in case fatality, the denominator is limited to those who already have the disease

Question 4

Proportionate mortality

Answer 4

Of all deaths in the US, it determines what proportion was caused by a certain disease. Proportionate mortality can change if the proportionate mortality of another disease changes. If proportionate mortality of cancer increases, the proportionate mortality of cancer would have to decrease since cancer is taking up more of the mortality “pie”. Proportionate mortality can give us a quick look at the major causes of death, but it cannot tell us the risk of dying from a disease

Question 5

Years of potential years lost (YPLL)

Answer 5

A measure of premature mortality (early death). In the US, the predetermined standard age is 75. The younger the age at which death occurs, the more years of potential years of life are lost. YPLL can assist in establishing and resource priorities, surveillance of temporal trends in premature mortality, and evaluating the effectiveness of program interventions

Question 6

Under which conditions is a mortality rate a good reflection of the incidence rate? (2)

Answer 6

1. When the case fatality is high- like untreated rabies, which is almost always fatal
2. When the duration of disease (survival) is short- like pancreatic cancer, which is almost always fatal and time of survival after diagnosis is usually short

Question 7

Increase in apparent incidence

Answer 7

Sometimes, a rise in incidence, like in thyroid cancer, is only an increase in apparent incidence. It does not reflect any true increase in new cases, but rather an increase in the early detection and diagnosis of subclinical cases. New diagnostic methods allow us to identify small and asymptomatic thyroid cancers that could not be detected previously.

Question 8

How are causes of death determined?

Answer 8

Deaths are coded according to the underlying cause. The underlying cause is the disease or injury that initiated the train of morbid events leading directly or indirectly to death or the circumstances of the accident or violence which produced the fatal injury.

Question 9

Which factor is the most important predictor of mortality?

Answer 9

Age

Question 10

Direct age adjustment

Answer 10

A standard population is used in order to eliminate the effects of any differences in age between 2 or more populations being compared. A hypothetical “standard” population is created to which we apply both the age-specific mortality rates from the later period. This technique eliminates the possibility that observed differences could be the result of age differences in the population

Question 11

Why are age-adjusted rates considered hypothetical?

Answer 11

Because they involve applying actual age-specific rates to a hypothetical standard population. They do not reflect the true mortality risk of a “real” population because the numerical value of an age-adjusted death rate depends on the standard population used. There is no “correct” standard population, but it is generally accepted that the standard shouldn’t be drastically different from the populations that are being compared with regard to age or another variable

Question 12

Indirect age adjustment

Answer 12

Used when numbers of deaths for each age-specific striatum are not available. Also used to study mortality in an occupationally exposed population- Do people who work in a specific industry have higher mortality than the rest of the population?

Question 13

Standardized mortality ratio (SMR)

Answer 13

The ratio of the total of deaths actually observed to the total number of deaths expected if the population of interest had the mortality experience of the known experience. An SMR of 100 indicates that the observed number of deaths is the same as the expected number of deaths. Greater than 100- the observed number of deaths is higher than expected

Question 14

Cohort effect

Answer 14

Variations over time, in one or more characteristics, among groups of individuals defined by some shared experience such as year or decade of birth, or years of a specific exposure. Any given population comprises multiple sub cohorts with different rates of exposures and outcomes.