Module 1 - GATE notes Ch 1

Question 1

What does GATE illustrate about all epidemiological studies?

Answer 1

All epidemiological studies have the same basic structure and they are all designed w the same objective - to measure how much dis-ease occurs in different groups/pop.s

Question 2

epidemiology = (i.e. the formula)

Answer 2

numerator/denominator i.e. (no. of people with dis-ease outcomes)/(no. of people in the study population)

Question 3

What is epidemiology? (not the formula)

Answer 3

Epidemiology is the study of how much dis-ease occurs in diff groups/pop.s & of the factors that determine differenced (variation) in the occurrence of dis-ease b/w these groups.

Question 4

Epidemiologists count dis-ease occurrence, define occurrence.

Answer 4

= the transition from a ‘non dis-eased state’ to a ‘dis-eased state’

Question 5

Define the term: population (as in epidemiological studies)

Answer 5

= any group of people who share one or more specified common factors e.g. demographic characteristics (age , gender, ethnicity), a time period, a dis-ease (e.g. heart disease) etc.

Question 6

Define health (or dis-ease)

Answer 6

The absence of death, disease or disability. OR The capacity to do what matters most to you. (^lecturer likes this def)

Question 7

What does measuring dis-ease occurrence in a pop or in different pop.s allow?

Answer 7

• single pop -> can inform health service planners about the services needed for the that pop. - different pop.s -> can investigate possible determinants (i.e. causes) or predictors of differences in dis-ease occurrence.

Question 8

Epidemiological studies collect data that can be counted (i.e. quantified). We can classify quantitative data as ___ or ___. Briefly describe these two.

Answer 8

• Categorical -> data that can be grouped into categories (e.g male/female, smokers/non-smokers) OR - Numerical -> data that take on numerical values (e.g. body weight, blood cholesterol levels)

Question 9

All good epidemiological studies begin by defining the denominator population, why is this?

Answer 9

B/c a key requirement of epidemiological studies is that the dis-ease outcomes counted in the numerator must come from a defined denominator population.

Question 10

(The GATE frame)

The triangle represents the ___

Answer 10

Participant population, i.e. the overall study denominator. e.g. 2000 men

Question 11

(The GATE frame)

1) The circle represents the ____
2) It is divided into ___

Answer 11

1) Study specific denominators
2) EG (exposure group/s) & CG (control group) = the denominators used in calculations.
e. g. EG = 400 men ‘exposed’ to smoking (i.e. smokers) & CG = 1600 ‘unexposed’ to smoking (i.e non-smokers)

Question 12

(The GATE frame)

1) The square represents the ____
2) What does each section represent?

Answer 12

1) The numerators (i.e. the dis-ease outcomes -> O)
2) Cell a -> people from EG in whom dis-ease occcurs,

Cell b -> people from CG in whom dis-ease occurs,

Cell c -> people from EG in who don’t get dis-ease,

Cell d -> people from CG in who don’t get dis-ease,

during the time over which the study is conducted.

Question 13

(The GATE frame)

What do the arrows represent? (basic explanation)

Answer 13

The arrows represent the time when or during which outcomes are measured.

Question 14

(The GATE frame)

What is the occurrence of dis-ease in each of EG & CG called? And what is the formula for this?

Answer 14

• dis-ease occurrence in EG = exposure group occurrence (EGO)
  
  • EGO = a/EG
• dis-ease occurrence in CG = comparison group occurrence (CGO)
  • CGO = b/CG

NOTE: we can measure occurrence of no dis-ease in EG (=c/EG) & CG (=d/CG)

Question 15

(The GATE frame)

Some numerical measures can be changed into categorical measures. Give an example of how this is possible in terms of salt consumption (= denominator) & blood pressure levels (= numerator)

Answer 15

Example:

• EG = high salt intake
• CG = medium or low salt intake
• outcomes: people w high blood pressure & people w medium/low blood pressure

We can then measure the occurrence of high (or low) b.p. in people w high salt intake (EGO) and the occurrence of high (or low) b.p. in people w low salt intake (CGO).

Question 16

(The GATE frame)

To calcualte dis-ease occurrence from numerical measures we can either convert the numerical measures to categorical measures or…

Give an example in terms of the salt & blood pressure example

Answer 16

or calculate the average level of the outcome in EG & CG.

Example:

• we can still classify salt categorically (i.e. high & medium or low intake).
• but can classify blood pressure numerically by calculating average blood pressure in each group.
• to calc disease occurrence:
  
  • add up b.p. level for every person in EG (high salt intake) & divide by the total no. of people in EG, to get the avg blood pressure level.
  • repeat for people in CG.
    
    • so EGO = (sum of a)/EG & CGO = (sum of b)/CG

Question 17

(The GATE frame)

In a ideal study using categorical data, everyone in EG & CG…

Answer 17

…ultimately gets classified as having a dis-ease outcome (a or b) or not having dis-eaase (c or d). Therefore:

• no. of people in EG should = no. of people in a & c
• no. of people in CG should = no. of people in b & d

Question 18

(Incidence & Prevalence)