404 ch 3

Chapter 3: 

Attack rate: determines the proportion of a population that develops a disease during an outbreak or a specific period

Ratio: “the value obtained by dividing 1 quantity by another” 

Rate: also a ratio, differs from a proportion b/c the denominator involves measure of time 

• Numerator: # of health events and Denominator: population in which event occur 

Proportion: type of ratio in which #part of the denominator

Percentage: a proportion that’s been multiplied by 100 

• Formula (A/A + B) x 100

Count: refers to the # of cases of a disease being studied (ex: one case of ebola virus) 

Lifetime Prevalence: cases diagnosed at any time during person’s lifetime (Ex: lifetime asthma prevalence) 

Point Prevalence: all cases of a disease that exist at a particular point in time relative to a specific population from which the cases are derived (ex: people w/ asthma at the time of interview) 

Prevalence: amount of total cases 

Incidence: amount of new cases 

Case Fatality Rate: 

Crude Rate: type of rate that has not been modified to take account of any of the factors like demographic makeup of the population that may affect observed rate 

• Includes time period in which event occurred 

• Aids in making comparison however has limitations

Death rate: expressed in terms of any unit size of a population that’s convenient (ex: infant mortality is expressed per 1000 live births)

Specific rates: 

1. Cause specific: measure that refers to mortality divided by the population size at the midpoint of time 

2. age specific: # of cases per age group of population during specified time period  

3. sex specific: frequency of disease in a gender group divided by the total # of persons within that gender group 

 Adjusted rate: rate of morbidity or mortality in a population in which statistical procedures have been applied to permit fair comparisons across populations by removing the effect of difference in the composition of various populations 

Measures related to Morbidity and Mortality: 

1. Crude rates 

2. Cause fatality rates

3. Proportional mortality ratio

4. Cause specific rates 

Measures related to natality: refers to the birth rate within a population 

1. Relationship between incidence and prevalence? 

   1. Incidence is the amount of new cases, while prevalence is the total amount of cases

2. What information is provided by epidemiologic measures?

   1. Provides frequency of disease or conditions 

   2. Associations b/exposures and health outcomes

   3. Strength of the relationship b/w an exposure and a health outcome 

3. Distinguish between fertility rate and birth rate

   1. Fertility: The average number of children a woman is expected to have during her reproductive years. 

   2. Birth rate: The number of live births per 1,000 people in a population per year

4. Discuss limitations w/ crude rates

   1. considers the entire population W/O adjusting for differences in age, sex

   2. do not provide insights into specific groups

Review questions: 

Know how to calculate: 

1. Incidence 

2. Prevalence

3. Crude death rate 

Factors that can increase or decrease an observed prevalence: 

1. Increase

   1. Increase in incidence 

   2. Longer duration of the case

   3. In-migration cases

   4. Prolongation of life of patients without a cure

2. Decrease

   1. Decrease in incidence 

   2. Shorter duration of disease 

   3. In-migration of healthy people 

   4. Improved cure-rate of disease 

Purpose of epidemiologic measures: 

1. Provides frequency of disease or conditions 

2. Associations b/exposures and health outcomes

3. Strength of the relationship b/w an exposure and a health outcome