WEEK 1 – Introduction to the field
CLIPS (1)
Epidemiology: an academic & applied science
Clinician → translates scientific knowledge and procedures to: “What is the best treatment
for this patient?”
Epidemiologist in academic setting → “How can you be sure about this exposure-effect,
independent of the context of this person on population?”
- Analysing the patterns and the causes; who, when, where, why.
- Knowledge generation
Epidemiologist in public health → “What is the best prevention strategy for this specific
population?”
- Using this information for prevention of the crimes
- Knowledge application
History of epidemiology and public health
Pre-formal epidemiology (1662-1900) → infectious diseases, nutritional deficiencies
- Became aware and started to count diseases
- Hygiene and sanitation
- People travelled over the world; infections imported & exported
- John Snow → preventing and counting cholera
Early epidemiology (1900-1940) → transition of acute infectious to chronic disease
- First prof in epidemiology
- Non-communicable diseases, pellagra, vitamins (chronic diseases)
Classical epidemiology (1940-1980) → chronic diseases
- Large scale epidemiological studies
- New methods and study designs
Modern epidemiology (1980-nu) → intervention trials
- Prevention strategies
DUS: Epidemiology provides knowledge about health and its determinants. It provides
foundation for Public Health interventions, policies and programmes.
1
,Descriptive epidemiology
Descriptive epidemiology = amount/frequency of disease or other conditions in a
population (what, who, when, where?) → beschrijven!
Analytical epidemiology = study of the causes of disease (why?) → based on facts collected
from groups of individuals (not large-scale population statistics)
The purpose of descriptive studies is to describe groups of people; necessary is a
representative sample! Why do we need these data?
- To evaluate the occurrence of health behaviours and health conditions
- To provide a basis for planning and evaluation of interventions
- For further analytic studies
Prevalence
The prevalence proportion measures the proportion of people in a population who have the
disease at a given point in time:
*so only the people who are screened
For example: What percentage/proportion of PREVELANCE = INCIDENCE x DURATION
the population has HIV right now?
➢ Point prevelance = number of people at a specific moment
➢ Period prevelance = number of people in a certain period
Incidence
The incidence measures how fast people are ‘catching’ the disease. LET OP! Considers all the
new people who gets the disease → prevalence all the existing cases.
Incidence Proportion (IP) / Cumulative Incidence (CI) = measures the proportion of people
who develop the disease during a specified period (NEW cases) → estimate of the average
risk of the persons in the cohort → ook wel berekenen van het risico!
COUNTING: number of people at risk; also people with a low
risk can be part of the population at risk
2
,Incidence Rate (IR) = number of people who develop a certain disease in a certain period
(bv. 5000 new cases per 100.000 people per year)
COUNTING: length of time they were at risk; the speed!
Person-years = sum of persons x time
If you know the time then calculate incidence rate! If you don’t
have time you cannot calculate this.
Incidence proportion (2nd screening) _NEW
x 100 = 3,9%
Prevalence (1st screening) _ ALREADY HAVE
x 100 = 5,1%
Closed / fixed population
- Based on fixed membership (nobody can get in or out)
- No one can be added
- But people may die, lost to follow-up etc.
- Becomes smaller with time
- Example: birth cohort → becomes smaller with time, everyone is followed
- Incidence proportion & Incidence Rate
Open / dynamic population
- Can take new members with time
- People move in and out of the area
- Numbers remain about the same
- Example: Wageningen University → numbers remain about the same, no follow-up
when leaving
- Incidence Rate only
- LET OP! Calculate the prevalence is not usefull. An injury for example is an acute event,
therefore at most of the time the prevalence will be 0. Or you do not know the number
of the existing cases at the moment.
3
, Relation between incidence and prevalence
If incidence is low, but duration is long (chronic),
prevalence will be large in relation to incidence.
If prevalence is low because of short duration
(due to recovery, migration or death),
prevalence will be small in relation to incidence.
Prevalence becomes smaller because of death
or cure.
LET OP! After introducing a large-scale screening programme for a disease, the incidence
figures of that disease often go up dramatically.
✓ Incidence is generally used for acutely acquired diseases… prevalence is used for
more permanent states, conditions or attributes of ill-health.
✓ Incidence is more important when thinking of etiology (=leer v/d oorzaken) of the
disorder… prevalence when thinking of societal burden (=maatschappelijke last) of
the disorder including the costs and resources consumed as a result of the disorder.
Introduction to diabetes
• Type 1 diabetes → auto-immune disease; no production
of insulin (develops in childhood and require lifelong
insulin injections)
• Type 2 diabetes (Mellitus) → metabolic disorder
characterized by hyperglycemia (=hoog bloedsuiker) and
altered lipid metabolism (develops in adulthood because
of unhealthy lifestyle)
• Gestational diabetes → state of hyperglycemia
developing during pregnancy
• Pre-diabetes → high risk at developing diabetes type II
Complications: stroke, heart disease, foot problems, renal disease, neuropathy (=slecht
werkende zenuwen)
LET OP! In medicine, they used to consider type 2 diabetes less influenced by genetics than
type 1, but science has made progress and new data show that it may not that straight
forward.
4
CLIPS (1)
Epidemiology: an academic & applied science
Clinician → translates scientific knowledge and procedures to: “What is the best treatment
for this patient?”
Epidemiologist in academic setting → “How can you be sure about this exposure-effect,
independent of the context of this person on population?”
- Analysing the patterns and the causes; who, when, where, why.
- Knowledge generation
Epidemiologist in public health → “What is the best prevention strategy for this specific
population?”
- Using this information for prevention of the crimes
- Knowledge application
History of epidemiology and public health
Pre-formal epidemiology (1662-1900) → infectious diseases, nutritional deficiencies
- Became aware and started to count diseases
- Hygiene and sanitation
- People travelled over the world; infections imported & exported
- John Snow → preventing and counting cholera
Early epidemiology (1900-1940) → transition of acute infectious to chronic disease
- First prof in epidemiology
- Non-communicable diseases, pellagra, vitamins (chronic diseases)
Classical epidemiology (1940-1980) → chronic diseases
- Large scale epidemiological studies
- New methods and study designs
Modern epidemiology (1980-nu) → intervention trials
- Prevention strategies
DUS: Epidemiology provides knowledge about health and its determinants. It provides
foundation for Public Health interventions, policies and programmes.
1
,Descriptive epidemiology
Descriptive epidemiology = amount/frequency of disease or other conditions in a
population (what, who, when, where?) → beschrijven!
Analytical epidemiology = study of the causes of disease (why?) → based on facts collected
from groups of individuals (not large-scale population statistics)
The purpose of descriptive studies is to describe groups of people; necessary is a
representative sample! Why do we need these data?
- To evaluate the occurrence of health behaviours and health conditions
- To provide a basis for planning and evaluation of interventions
- For further analytic studies
Prevalence
The prevalence proportion measures the proportion of people in a population who have the
disease at a given point in time:
*so only the people who are screened
For example: What percentage/proportion of PREVELANCE = INCIDENCE x DURATION
the population has HIV right now?
➢ Point prevelance = number of people at a specific moment
➢ Period prevelance = number of people in a certain period
Incidence
The incidence measures how fast people are ‘catching’ the disease. LET OP! Considers all the
new people who gets the disease → prevalence all the existing cases.
Incidence Proportion (IP) / Cumulative Incidence (CI) = measures the proportion of people
who develop the disease during a specified period (NEW cases) → estimate of the average
risk of the persons in the cohort → ook wel berekenen van het risico!
COUNTING: number of people at risk; also people with a low
risk can be part of the population at risk
2
,Incidence Rate (IR) = number of people who develop a certain disease in a certain period
(bv. 5000 new cases per 100.000 people per year)
COUNTING: length of time they were at risk; the speed!
Person-years = sum of persons x time
If you know the time then calculate incidence rate! If you don’t
have time you cannot calculate this.
Incidence proportion (2nd screening) _NEW
x 100 = 3,9%
Prevalence (1st screening) _ ALREADY HAVE
x 100 = 5,1%
Closed / fixed population
- Based on fixed membership (nobody can get in or out)
- No one can be added
- But people may die, lost to follow-up etc.
- Becomes smaller with time
- Example: birth cohort → becomes smaller with time, everyone is followed
- Incidence proportion & Incidence Rate
Open / dynamic population
- Can take new members with time
- People move in and out of the area
- Numbers remain about the same
- Example: Wageningen University → numbers remain about the same, no follow-up
when leaving
- Incidence Rate only
- LET OP! Calculate the prevalence is not usefull. An injury for example is an acute event,
therefore at most of the time the prevalence will be 0. Or you do not know the number
of the existing cases at the moment.
3
, Relation between incidence and prevalence
If incidence is low, but duration is long (chronic),
prevalence will be large in relation to incidence.
If prevalence is low because of short duration
(due to recovery, migration or death),
prevalence will be small in relation to incidence.
Prevalence becomes smaller because of death
or cure.
LET OP! After introducing a large-scale screening programme for a disease, the incidence
figures of that disease often go up dramatically.
✓ Incidence is generally used for acutely acquired diseases… prevalence is used for
more permanent states, conditions or attributes of ill-health.
✓ Incidence is more important when thinking of etiology (=leer v/d oorzaken) of the
disorder… prevalence when thinking of societal burden (=maatschappelijke last) of
the disorder including the costs and resources consumed as a result of the disorder.
Introduction to diabetes
• Type 1 diabetes → auto-immune disease; no production
of insulin (develops in childhood and require lifelong
insulin injections)
• Type 2 diabetes (Mellitus) → metabolic disorder
characterized by hyperglycemia (=hoog bloedsuiker) and
altered lipid metabolism (develops in adulthood because
of unhealthy lifestyle)
• Gestational diabetes → state of hyperglycemia
developing during pregnancy
• Pre-diabetes → high risk at developing diabetes type II
Complications: stroke, heart disease, foot problems, renal disease, neuropathy (=slecht
werkende zenuwen)
LET OP! In medicine, they used to consider type 2 diabetes less influenced by genetics than
type 1, but science has made progress and new data show that it may not that straight
forward.
4
