PPHC 07: Evidence Evaluation (Epidemiology) – How do we measure disease?

Question 1

What is epidemiology?

Answer 1

science of distribution (person, place, time) and frequency (incidence, prevalence) of disease

Question 2

What can epidemiology do? (4)

Answer 2

• describe health of a population
• explain cause of disease
• predict occurrence of disease
• control distribution of disease

Question 3

What are the assumptions of epidemiology? (2)

Answer 3

• disease does not occur randomly
• disease has casual and preventative factors that we can identify through systematic investigation of different people at different places or times

Question 4

What are the 3 types of epidemiology and their goal?

Answer 4

• descriptive epidemiology
• analytic epidemiology
• experimental epidemiology

Question 5

What is the goal of descriptive epidemiology?

Answer 5

examine patterns (of disease, health behaviours)

Question 6

What is the goal of analytic epidemiology?

Answer 6

evaluate relationships between risk/protective factors and disease

Question 7

What is the goal of experimental epidemiology?

Answer 7

evaluate effect of treatment/intervention on disease

Question 8

What is rank?

Answer 8

measures the order of disease occurrence

• ie. cancer is the #1 leading cause of death in Canada
• ie. arthritis and other rheumatic conditions are leading cause of work disability among US adults
• ie. diabetes is the 7th leading cause of death in the US

Question 9

What is count(s)?

Answer 9

measure(s) the number of persons who have a given disease

• no denominator
• ie. 229,200 Canadians will be diagnosed with cancer in 2021
  ie. 84,600 Canadians will die from cancer in 2021
  ie. number of female(s) with disease X

Question 10

What is ratio?

Answer 10

quotient of two numbers, where numerator is not necessarily included in the denominator (no specific relationship between numerator and denominator) – allows comparison of quantities of different nature

• ie. family doctors in BC to number of British Columbians
• ie. male to female ratio

Question 11

What ratios are there in epidemiologic studies?

Answer 11

measures of association

• relative risk/risk ratio (RR)
• odds ratio (OR)

Question 12

What is proportion?

Answer 12

quotient of two numbers, where numerator is necessarily included in the denominator

• expressed as fraction, decimal, or percentage
• ie. 2 in 5 Canadians will develop cancer in their lifetime
• ie. 1 in 4 Canadians will die from cancer

Question 13

What is rate?

Answer 13

quotient of two numbers, where:

• numerator: number of ‘events’ (new cases of disease) observed for a given time
• denominator: population in which events occur, includes time
• ie. 5-year cancer survival rate is about 64% – ratio of people who are live for 5 years after cancer diagnosis to people in the general population who are alive over the same 5 year period

Question 14

What is prevalence?

Answer 14

all individuals (proportion of a population) affected by disease at a particular time

• refer to individuals as ‘prevalent cases’ or ‘active cases’
• usually expressed as a percentage

Question 15

What are the 2 types of prevalence?

Answer 15

• point prevalence
• period prevalence

Question 16

What is point prevalence?

Answer 16

proportion of a population affected by a disease at a point in time

• ie. prevalence of type 2 diabetes on December 31, 2020

Question 17

What is period prevalence?

Answer 17

proportion of a population affected by a disease during a certain period of time

• ie. prevalence of diabetes in 2020

Question 18

What is incidence?

Answer 18

number of new individuals with a disease during a particular period of time

• refer to individuals as ‘incident cases’ or ‘new cases’

Question 19

What are the 2 types of incidence?

Answer 19

• incidence proportion (cumulative incidence)
• incidence rate (incidence density) – ‘person-time’

Question 20

What is incidence proportion (cumulative incidence)?

Answer 20

number of new cases of disease over period of time divided by number of individuals at risk for disease at beginning of time period

Question 21

What is incidence rate (incidence density)?

Answer 21

time each person was observed

• 1 person at risk of a disease observed for 1 year = 1 person-year
• 2 person at risk of a disease observed for 1 month = 1 person-month
• 10 cases per 1000 person-years
• 1 case per 100 person-years
• 0.1 cases per 10 person-years
• 0.01 cases per 1 person-year

Question 22

What is prevalence (‘disease burden’) used for?

Answer 22

• measure population disease status
• help plan healthcare delivery
• indicate groups who should be targeted

Question 23

What is incidence (‘disease risk’) used for?

Answer 23

• assess frequency of disease onset
• estimate risk of disease development
• study risk factors for disease
• evaluate preventive interventions