Voortgezette
Statistiek en
Methoden van
Onderzoek
Door
NINA VAN TILBURG
Maastricht University
Faculty of Health, Medicine and Life Sciences
(FHML)
GZW3024
Year 3, Block 4
,Onderwerpen van statistiek:
• Measures of disease frequency & study designs
• lecture 1
• seminar 1 & 4
• Linear regression
• lecture 2 & 3
• seminar 2 & 3 & 5
• practical 1
• Bias, effect modification and interaction
• lecture 4
• seminar 6
• Logic regression
• lecture 5
• seminar 7 & 8
• practical 2
• Marginal models
• lecture 6
• seminar 10 & 12
• practical 3
• Experimental studies
• lecture 7
• seminar 9 & 11 (experimental research)
• Validity, reliability and responsiveness
• lecture 8
• seminar 13
• Betrouwbaarheid, validiteit & Overeenstemming (B, V &O)
• lecture 10 & 12
• seminar 15 & 16 & 18
• practical 4
• Causality & Causal interference
➢ lecture 13
➢ Seminar 19 & 20
• Power and choice of analysis technique
• lecture 14
• seminar 22 & 23 & 24 & 25
• practical 5
, MEASURES OF DISEASE FREQUENCY & STUDY DESIGNS
Lecture 1, Seminar 1 & 4
Lecture 01 – Measures of disease frequency & observational study design
Measures of disease frequency
= the used term for epidemiologists to describe occurrence of disease.
Most common used terms are prevalence and incidence
o Both measures relate the number of disease cases to the population risk.
‘DESCRIPTIVE’ EPIDEMIOLOGY
Prevalence:
= all existing cases (people who already have the disease, no matter when it started)
o Point Prevalence = Part of the population that is diseased at a certain point in time.
E.g. point prevalence of arthrosis NL 65+ on 01-01-2025: 21%
o Period Prevalence = Part of the population that is diseased within a time period.
E.g. ‘common cold’ among UM employees during 2024: 68%
Note – use the mid-term population if Nbegin ≠ Nend
o Life-time Prevalence = Part of population that was diseased during life.
E.g. life-time prevalence of kidney stones among Dutch men: 12%
Incidence:
= relates to the number of new cases (people who just developed the disease)
o Cumulative incidence (CI)
o Incidence Density (ID), or Incidence Rate
- Depending on type of population (closed or dynamic) CI or ID is used.
Types of populations:
Cohort (=closed population)
o Membership
- T0: a certain event (e.g. birth)
- Tend: indefinite
o Follow-up
- Tend: disease/death/loss to follow-up/end of study
o Examples
- Students GZW3024 (2025_2026)
- Birth cohort 1973
- Randomized Controlled Trial participants
Dynamic Population
o Membership
- Typically variable
o Follow-up
- T0: variable
- Tend: disease/death/loss to follow-up/end of study
2
, o Examples
- Inhabitants of Maastricht
- Patients intensive care unit
Cumulative Incidence (CI):
o Size of the study population does not change over time = closed population (cohort)!!!
o The CI is noted in %
o All members of the population are ‘at risk’ at, therefore it is important to exclude all
the prevalent cases! This is because they are not at risk, because they already have the
disease.
o Period P in the formula – complete follow-up of all members of the population is
required ~ loss to follow-up is unwanted.
o For the interpretation – Absolute Risk – which is the mean individual risk during
follow-up.
Incidence Density (ID), Or Incidence Rate:
o The ID is noted as year-1 (=rate: number/time)
o It is not required that the follow-up of the population is complete (dynamic and closed
population/cohort possible).
Prevalence = Incidence * average disease duration →
Relevant measures for epidemiology of infectious diseases
R0: Basic reproduction number
o How many people one infected person will infect when everyone is still susceptible
(no immunity in the population).
Rt: Effective reproduction number at time t
o How many people one infected person infects
at a specific moment, taking into account immunity
and control measures.
Attack rate:
o The chance (in percent) that someone will get the infection after being in contact with
an infected person.
Reproduction number Rt = Attack Rate * contacts
3
Statistiek en
Methoden van
Onderzoek
Door
NINA VAN TILBURG
Maastricht University
Faculty of Health, Medicine and Life Sciences
(FHML)
GZW3024
Year 3, Block 4
,Onderwerpen van statistiek:
• Measures of disease frequency & study designs
• lecture 1
• seminar 1 & 4
• Linear regression
• lecture 2 & 3
• seminar 2 & 3 & 5
• practical 1
• Bias, effect modification and interaction
• lecture 4
• seminar 6
• Logic regression
• lecture 5
• seminar 7 & 8
• practical 2
• Marginal models
• lecture 6
• seminar 10 & 12
• practical 3
• Experimental studies
• lecture 7
• seminar 9 & 11 (experimental research)
• Validity, reliability and responsiveness
• lecture 8
• seminar 13
• Betrouwbaarheid, validiteit & Overeenstemming (B, V &O)
• lecture 10 & 12
• seminar 15 & 16 & 18
• practical 4
• Causality & Causal interference
➢ lecture 13
➢ Seminar 19 & 20
• Power and choice of analysis technique
• lecture 14
• seminar 22 & 23 & 24 & 25
• practical 5
, MEASURES OF DISEASE FREQUENCY & STUDY DESIGNS
Lecture 1, Seminar 1 & 4
Lecture 01 – Measures of disease frequency & observational study design
Measures of disease frequency
= the used term for epidemiologists to describe occurrence of disease.
Most common used terms are prevalence and incidence
o Both measures relate the number of disease cases to the population risk.
‘DESCRIPTIVE’ EPIDEMIOLOGY
Prevalence:
= all existing cases (people who already have the disease, no matter when it started)
o Point Prevalence = Part of the population that is diseased at a certain point in time.
E.g. point prevalence of arthrosis NL 65+ on 01-01-2025: 21%
o Period Prevalence = Part of the population that is diseased within a time period.
E.g. ‘common cold’ among UM employees during 2024: 68%
Note – use the mid-term population if Nbegin ≠ Nend
o Life-time Prevalence = Part of population that was diseased during life.
E.g. life-time prevalence of kidney stones among Dutch men: 12%
Incidence:
= relates to the number of new cases (people who just developed the disease)
o Cumulative incidence (CI)
o Incidence Density (ID), or Incidence Rate
- Depending on type of population (closed or dynamic) CI or ID is used.
Types of populations:
Cohort (=closed population)
o Membership
- T0: a certain event (e.g. birth)
- Tend: indefinite
o Follow-up
- Tend: disease/death/loss to follow-up/end of study
o Examples
- Students GZW3024 (2025_2026)
- Birth cohort 1973
- Randomized Controlled Trial participants
Dynamic Population
o Membership
- Typically variable
o Follow-up
- T0: variable
- Tend: disease/death/loss to follow-up/end of study
2
, o Examples
- Inhabitants of Maastricht
- Patients intensive care unit
Cumulative Incidence (CI):
o Size of the study population does not change over time = closed population (cohort)!!!
o The CI is noted in %
o All members of the population are ‘at risk’ at, therefore it is important to exclude all
the prevalent cases! This is because they are not at risk, because they already have the
disease.
o Period P in the formula – complete follow-up of all members of the population is
required ~ loss to follow-up is unwanted.
o For the interpretation – Absolute Risk – which is the mean individual risk during
follow-up.
Incidence Density (ID), Or Incidence Rate:
o The ID is noted as year-1 (=rate: number/time)
o It is not required that the follow-up of the population is complete (dynamic and closed
population/cohort possible).
Prevalence = Incidence * average disease duration →
Relevant measures for epidemiology of infectious diseases
R0: Basic reproduction number
o How many people one infected person will infect when everyone is still susceptible
(no immunity in the population).
Rt: Effective reproduction number at time t
o How many people one infected person infects
at a specific moment, taking into account immunity
and control measures.
Attack rate:
o The chance (in percent) that someone will get the infection after being in contact with
an infected person.
Reproduction number Rt = Attack Rate * contacts
3
