CE/CH/ENV-54: Homework 2, Spring 2008
A new treatment is developed that prolongs the life of individuals suffering from a particular chronic
This disease affects men and women over 65 years of age.
Without the new treatment, death within
2 years of diagnosis is typical.
With the new treatment, it is estimated that affected individuals will die in 7-
Considering these facts, answer the following three questions.
Be sure to adequately explain your
How will the new treatment affect the incidence of the disease?
Since incidence is calculated in a given
time period and this is a chronic disease, the treatment will not necessarily reduce incidence.
It does not
prevent people from getting the disease (which would decrease the number in the numerator of the incidence
Furthermore, a chronic disease indicates that once people have the illness, they will have it for the
rest of the calculated time period so the treatment, which just prolongs the amount of time they will live, will
not change person time (unless the patient dies).
How will the new treatment affect the prevalence of the disease?
It will slightly increase prevalence.
Given that the treatment increases life expectancy, there will be more people aged 65+ alive with the disease
at any given time.
In people 65+, how do you expect the overall mortality rate from this disease will be affected by the new
Again, this is a chronic disease that tends to kill the patients eventually, and the treatment just
prolongs their life.
The mortality rate might decrease slightly but only because other age-related factors may
kill the sick people before the disease does—there is more time for other health problems to arise with the
new treatment (so the death would be blamed on something else).
Assume all information is the same except that this illness can affect anyone 40 years of age or older.
In people 50-59, how do you expect the overall mortality rate from this disease will be affected by the
In people 40-49?
In people 60+?
As in 1c, the overall mortality rate will probably decrease
a little bit.
With the extended time patients have to live, there is a higher chance other things could kill them
before the disease does, but it is still a chronic disease with a limited life expectancy after diagnosis.
Consider the following two incidence graphs of two diseases (note: Males = top line, male and female =
middle line, female = bottom line.
For the questions, you should just ignore the middle line).
For each of the
following, state whether you can or cannot answer using just the information contained in the two graphs.
can answer, do so.
If you cannot, state why not.