Exercise to practice measures of disease frequency

State which type of mathematical parameter (ratio/proportion/rate) and which type of measure of disease frequency (cumulative incidence/incidence rate/prevalence) best describes each of the following.

1. Percentage of infants enrolled in a day-care center who contracted impetigo during the course of an epidemic.
2. Percentage of potential army recruits rejected because of poor vision.
3. Number of colds experienced in a year per thousand people.
4. Percent of persons who have malaria that is resistant to treatment with chloroquine.

Which of the above measures would be the best indicator for each of the following purposes?
a. Determining the effectiveness of a new treatment
b. Evaluating the effectiveness of a program that tries to prevent the disease
c. Estimating the needs for medical facilities in treating the disease

1: Attack rate (cumulative incidence). Percentages are always proportions.
2: Prevalence proportion. Again, the key word is "percentage".
3: Incidence rate. (cumulative incidence is also acceptable). The events in the numerator may either be experienced multiple times by the same person (colds, myocardial infarctions) or may be unique in an individual's lifetime (first diagnosis of cancer, death).
4: Prevalence proportion.

A: Case Fatality Rate, Mortality Rate, Prevalence
B: Cumulative Incidence
C: Prevalence, Incidence