EPI/STATS - Measures of Mortality

Question 1

INCIDENCE

Answer 1

Cumulative Indicidence = (# new events at time t)/(population at risk)

Person-Year = (# of people affected)*(years of observation)

Incidence Density (Person-Year Incidence) = (# of new events at time T)/(person-years)

Prevalence = incidence*duration

Question 2

PREVALENCE

Answer 2

Prevalence = Incidence*Duration

Increased incidence = increased prevalence

BUT, increased prevalence doesn’t necessary = increased incidence

Prevalence also increased by increased recovery (better treatment, new treatment) and increased death

Question 3

IMPORTANCE OF INCIDENCE AND PREVALENCE

Answer 3

Incidence –> helps understand risk factors, prevention, and etiology

Prevalence –> aids in providing health services (to estimate resources)

Question 4

MORTALITY RATES

Answer 4

Crude mortality rate = # of deaths/population

Age-adjustment = adjusted to age and population

Case mortality rate = (# of deaths from disease)/(# of cases of disease)

Proportionate mortality rate = (# of deaths from disease)/(total # of deaths in population)

Question 5

RISK

Answer 5

Relative risk (RR) = (incidence among treated or exposed)/(incidence among not treated or exposed)

• RR = 1, no difference in risk between exposed and non-exposed groups
• Same as Hazard Ratio (HR) and Odds Ratio (OR)
• Can be increased by an increase in treatment population with a negative outcome or by a decrease in non-treatment population with a negative outcome

Attributative risk (AR) = (incidence of exposed - incidence of not exposed)

• AR = 0, no difference in risk between exposed and non-exposed groups
• Same as risk reduction, risk difference, or absolute risk

Number needed to treat (NNT) = 1/AR

Question 6

CONFOUNDING VARIABLE

Answer 6

1. Confounder is a risk factor in the disease (independent of the putative risk factor)
2. Confounder is associated with the putative risk factor
3. Confounder is not a casual factor in the pathway to disease (does not cause the putative risk factor to occur)

Question 7

EFFECT MODIFIER

Answer 7

• A variable that changes the effect (+ or -) when it is present. Stratifies variables
• Ex: effect of aspirin on reducing heart disease.
  
  • Effect modifier = gender
• Ex: number of miscarriages by HS mothers
  
  • Effect modifier = smoking vs nonsmoking HS mothers