Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence...
-
Upload
hortense-rice -
Category
Documents
-
view
215 -
download
1
Transcript of Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence...
![Page 1: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/1.jpg)
Epidemiology
![Page 2: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/2.jpg)
1. What is epidemiology and what are its uses?
2. Descriptive epidemiology– Incidence and prevalence– Qualitative information
3. Analytical epidemiology – Types of studies– Association and causation
![Page 3: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/3.jpg)
What is Epidemiology?
“The study of the frequency, distribution and determinants of health problems and disease in human populations”
The unit of interest is the population
![Page 4: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/4.jpg)
Purpose of epidemiology
“To obtain, interpret and use health information to promote health and reduce disease”
![Page 5: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/5.jpg)
How does Epidemiology help?
It allows the distribution of health and illness in a population to be described in terms of:
– WHERE and WHEN does this health problem occur in the population?
– WHAT is the problem and its frequency?
– WHO is affected?
– WHY does it occur in this particular population?
![Page 6: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/6.jpg)
How does Epidemiology help? (2)
Epidemiological information is used to:
– Prevent illness and promote health
– To help treat people with existing disease
– Evaluate existing health services
![Page 7: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/7.jpg)
Epidemiological Studies
Descriptive Analytic
Observational Experimental
![Page 8: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/8.jpg)
What is descriptive epidemiology?
Frequency (of disease) (incidence & prevalence)
+Distribution (of disease)
=“descriptive epidemiology”
![Page 9: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/9.jpg)
Descriptive epidemiology
• Usually makes use of routinely collected data, (e.g. death certification data, hospital episode statistics, infectious disease notifications)
• May require special surveys (usually cross sectional)
• Can’t answer ‘why?’ but can raise a causal hypothesis
• Can often provide sufficient information for public health action to be taken
![Page 10: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/10.jpg)
TIME, PLACE, PERSON
• Time: Trends, seasonal variations, cohort effects…
• Place: Variations between geographical areas – local, national, international…
• Person: Variations in health by age, sex, ethnicity, occupation, leisure interests...
– All help us examine variations (inequalities) in health
![Page 11: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/11.jpg)
Example 1: Pneumococcal meningitis incidence rate per 100,000 population by age group, England and Wales, 1996-2005 (Source HPA surveillance data)
![Page 12: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/12.jpg)
Public Health ActionOn 4th September 2006 Pneumococcal
vaccinationintroduced into childhood immunisation
schedule!
![Page 13: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/13.jpg)
Cumulative weekly number of reports of Invasive Pneumococcal Disease due to any of the seven serotypes in Prevenar™ : Children aged < 2 Years in England and Wales by
Epidemiological Year: July-June (2003- To Date)
![Page 14: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/14.jpg)
Example 2
Why might death rates in the UK be high?
![Page 15: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/15.jpg)
Descriptive epidemiology
• By studying frequency and distribution we can describe patterns of disease
• This can raise further questions and help us to generate hypotheses for the causes of disease
• It also helps us to respond to public health problems
![Page 16: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/16.jpg)
Measures of disease frequency
There are 2 major types of measure of disease frequency:
Incidence
Prevalence
![Page 17: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/17.jpg)
What is incidence?
The incidence is the number of NEW CASES of disease that develop, in a population of individuals at risk, during a specified time period
Usually expressed as the number of new cases, per 100,000 population per year
![Page 18: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/18.jpg)
Example 3: Measuring incidence
Incidence of cervical cancer in a PCT during 2002
– Number of new cases during 2002 = 18
– Number of disease-free persons (‘population at risk’) at the beginning of 2002 = 200,000
Incidence is (18/200,000) x 100,000
– 9 cases of cervical cancer per 100,000 in 2002
N.B. The denominator might be taken as the population at risk at the beginning, or the mid-point of the year, or the total person-time at risk
![Page 19: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/19.jpg)
What is prevalence?
Prevalence is the total number of EXISTING CASES of disease in a population at one point in time.
It is expressed as a proportion of the total number of persons in that population.
Also referred to as “point prevalence”
Period prevalence is a variation which represents the number of persons who were a case at any time during a specified period, as a proportion of the total number of persons in that population
![Page 20: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/20.jpg)
Prevalence
• Prevalence is expressed as a proportion(0-100%)
…or as a rate (e.g. X cases per 100,000 population)
• It does not take into account WHEN people became infected / diseased
![Page 21: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/21.jpg)
Example 4: Labouring the point!Incidence and prevalence
Cases of cold infections in class 4J. Class size: 20January February March
What is the period prevalence during February?
What is the point prevalence on the 28th February?
What is the incidence in February?
6/20 = 30%
1/20 = 5%
4/?
![Page 22: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/22.jpg)
Incidence and prevalence
Sick population
(Prevalence)Healthy
population
Incidence (new cases)
die (mortality)
recover
![Page 23: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/23.jpg)
Epidemiological Studies
Descriptive Analytic
Observational Experimental
![Page 24: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/24.jpg)
Analytic epidemiology
Descriptive epidemiology (who, what, when)
+Analysis of cause and effect
(why, how)=
“analytic epidemiology”
![Page 25: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/25.jpg)
Example 5: John Snow
• John Snow, physician (1813-1858)
• Outbreaks of Cholera were common in London during the 19th century
• But what was causing the cholera? The popular theory at the time was that bad gases caused it (‘miasma’ theory)
![Page 26: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/26.jpg)
What did he do?
Analysis by place: he mapped the cases – most were near Broad Street (…miasma would predict even spread)
Anecdote: People had complained that the water smelt bad. Cases from further afield had water delivered by cart from Broad Street.
![Page 27: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/27.jpg)
Public health action
He removed the handle from the Broad Street pump and the number of infections fell.
![Page 28: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/28.jpg)
What did he do?
Recorded deaths by water supplier
The Lambeth company had started to pump water from 20 miles upstream from the Thames
Conclusion: Risk of infection is highest in people using water from the Southwark and Vauxhall water company.
![Page 29: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/29.jpg)
Types of analytical study
Observational studies– Cross-sectional study
– (may be descriptive or analytical)
– Case control study– Cohort study
Intervention study (experimentation)– Randomised controlled trial (RCT)
![Page 30: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/30.jpg)
Cross-sectional study
• Information on health status and other characteristics is collected from each subject at one point in time
• Cross-sectional studies can be descriptive…(eg. the prevalence of cough in a population)
• Or analytical…(eg. the association between cough and risk factors such as type of house lived in or whether person is a smoker)
![Page 31: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/31.jpg)
Example 6: cross sectional study
A cross sectional survey of adult dental health in Cornwall, in 1996.Aims:
• to provide a baseline measure of dental health status (descriptive)
• to compare dental health status in deprived and affluent neighbourhoods (analytical)
![Page 32: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/32.jpg)
Sampling method
+………..….Townsend score ……...…..…-
deprivede.d.s
randomly selectede.d.s
affluente.d.s
Using deprivation data from the 1991 census, participants were selected from the most deprived and the most affluent enumeration districts, and a random selection of e.d.s in between.
![Page 33: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/33.jpg)
Survey of adult dental health in Cornwall
Proportion of each subgroup in "poor dental health"
0%
5%
10%
15%
20%
25%
30%
35%
40%
45%
25-34 years 45-54 years
Age
deprived
aff luent
county
Deprived people in both age groups were more likely than affluent people to be in poor dental health.
![Page 34: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/34.jpg)
After difficulty in finding a dentist, what was the outcome?
0
10
20
30
40
50
60
70
deprived 25-34 yrs
deprived 45-54 yrs
affluent 25-34 yrs
affluent 45-54 yrs
county 25-34 yrs
county 45-54 yrs
%
gave up private NHS
PH action: grants for service development targeting high need areas.
Most people in deprived areas eventually found an NHS dentist, or gave up.
People in more affluent areas were more likely to pay privately for treatment.
![Page 35: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/35.jpg)
Case-control study
• Compares people with a condition (cases) to a similar group of people without the condition (controls)
• The aim is to try and identify the risk factors which may have caused the cases to get the condition in the first place
• Often used to investigate the source of an outbreak of disease.
![Page 36: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/36.jpg)
Example 7: Case control study
What caused an outbreak of Salmonella in south east Wales?
• A case control study of people in SE Wales examined their diet and behaviour during the 3 days before illness
• Those who were ill were found to have been 4.5 x more likely to have eaten sliced ham than those who were not ill
• Further investigations revealed that those who were ill were 25 x more likely to have eaten ham supplied by “producer A”
![Page 37: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/37.jpg)
Outcome
Exposure 1
Exposure 2
Exposure 3
Exposure 4
Case (Person with outcome)
Exposure
Control (Person without the outcome
![Page 38: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/38.jpg)
Cohort Study
• Follow up two groups of people over time and compare the occurrence of disease
• One group is exposed to a possible risk factor for the disease, while the other is not (the control group)
• The exposure is the starting point, the disease is the outcome of interest
![Page 39: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/39.jpg)
Example 8: Cohort study
• Does being exposed to asbestos cause respiratory cancer?
• Asbestos miners were followed up for 6 years. These were compared to the control group
• Asbestos miners were 50% more likely to die of respiratory cancer than the control group.
![Page 40: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/40.jpg)
Population
Exposed
Unexposed
Outcome
Outcome
Exposure Outcomes
![Page 41: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/41.jpg)
• Cohorts can be retrospective too
• The starting point is still the EXPOSURE
• Outbreak of salmonella amongst guests at a wedding
• Use wedding menu to identify potential exposures and then survey the guests
• Identify most likely source of the outbreak
Cohort Study (2)
![Page 42: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/42.jpg)
Measures of Disease Frequency
The most basic measure of disease frequency is a simple count of affected individuals.
However, counting is not enough!
![Page 43: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/43.jpg)
Why is a simple count not enough?
• 3 cases of cancer per year from a city of 1,000 people is very different than 3 cases per year from a city of 100,000 people
![Page 44: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/44.jpg)
So, in epidemiology we must know:
• the size of the population from which the affected individuals come, and
• the time period the information was collected.
![Page 45: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/45.jpg)
Basic Measure of Disease Frequency
• Rate – an example: Incidence
![Page 46: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/46.jpg)
Rate
• basic measure in epidemiology
• the frequency with which an event occurs in a group of people
• used to compare the occurrence of disease in different groups
![Page 47: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/47.jpg)
Example: Rates
Rate = Number of events in a specified time period Average population during the time period
***the measure of time is a critical part of a rate!
Such as, the number of newly diagnosed cases of breast cancer per 100,000 women during 1999.
![Page 48: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/48.jpg)
Common Rates
• mortality (death) rate is the number of deaths in a defined group of people during a specified time period.
• birth rate is the number of live births in a defined group of people over a specified time period.
![Page 49: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/49.jpg)
Incidence
• a type of rate
• the number of new cases that develop in a group of individuals during a specific time period
![Page 50: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/50.jpg)
Incidence (cont.)
I = number of new events during a period of time
number of persons at risk during this time period
![Page 51: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/51.jpg)
Example: Incidence
If there were 150,00 new cases of lung cancer in the United States during 1997, the incidence rate would be:
(150,000/260,000,000) = 0.000058 0.000058 x 100,000 people
= 58 cases per 100,000 people, per year
![Page 52: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/52.jpg)
Measures of Association
• How much greater the frequency of disease is in one group compared with another.
• Often presented in the form of a two-by-two table.
![Page 53: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/53.jpg)
Two-By-Two Table
a b
c d
Disease
Yes No
Yes
Exposure
No
Total a+c b+d
Total
a+b
c+d
a+b+c+d
![Page 54: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/54.jpg)
Hypothetical Two-By-Two Table
70 300
15 700
Lung cancer
Yes No
Yes
Smoking
No
Total 85 1,000
Total
370
715
1,085
![Page 55: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/55.jpg)
Relative Risk (RR)
• Measures how likely the exposed group will develop a disease compared to the unexposed group.
RR = incidence in the exposed = a/(a+b)incidence in the unexposed
c/(c+d)
![Page 56: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/56.jpg)
Example: Hypothetical Study
Lung cancer
Yes No Total
Yes 70 300 370
Smoking No 15 700 715
Total 85 1,000 1,085
![Page 57: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/57.jpg)
Relative Risk = 70/(70+300) = 9.0 15/(15+700)
Which means… participants who smoked were 9 times more likely to develop lung cancer than those who did not smoke.
![Page 58: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/58.jpg)
Interpreting Measures of Association
RR of 1.0 indicates that the occurrence of disease in the exposed an unexposed groups are identical:
–No association observed between exposed and unexposed groups.
![Page 59: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/59.jpg)
Interpreting Measures of Association (Continued)
• RR greater than 1.0 indicates a positive association, or an increased risk among the exposed.
• RR less than 1.0 means that there is a decreased risk among the exposed group.
![Page 60: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/60.jpg)
Standardized Mortality Ratios (SMRs)
• the ratio of the observed number of deaths to the expected number of deaths
• a standard group of people is used to determine the expected number of deaths – the standard is often the US population, a state, or
a county.– serves as the comparison group
![Page 61: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/61.jpg)
SMRs (Continued)
Calculation:
SMR = observed deathsexpected deaths
![Page 62: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/62.jpg)
Example: Study of Smoking and Lung Cancer
Our hypothetical study found 58 lung cancer deaths between 1948 and 1963:
– based on US population rates, we know that 42.9 cancer deaths were expected in a similar population.
SMR = (58/42.9) =1.35
![Page 63: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/63.jpg)
Example: Study of Smoking and Lung Cancer (cont.)
Our study group had a risk of cancer mortality approximately 35% greater than those in the general population.
![Page 64: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/64.jpg)
Measuring Exposure and Measuring Outcomes in
Environmental Epidemiology
• Contaminants in air, water, food, or soil come in contact with people through swallowing, breathing, or skin contact
• Once the contaminant gets in the body, it can act at that point of entry or can be distributed throughout the body where it can act upon a target organ or organs
![Page 65: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/65.jpg)
Measuring Exposure• We can measure exposures or their surrogates along the
entire path from emissions to body burden
Types of Data Approximation to actual exposure_________________________________________________________________________1) Residence in a defined geographical Poorestarea (e.g. county) of a site |2) Residence in a geographical area in |proximity to to a site where exposure is assumed |3) Distance or duration of residence |4) Distance and duration of residence |5) Quantified surrogate of exposure (e.g. estimate |of drinking-water use |6) Quantified area measurements in vicinity of the |residence |7) Quantified personal measurement Best
Baker D, et al., Environmental Epidemiology: A Textbook on Study Methods and Public Health Applications, 1999
![Page 66: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/66.jpg)
What is an Outcome or Adverse Health Effect?
• Any change in health status or body function.
– Wide spectrum of effects such as wheezing, change in immune function, changes in blood chemistry, DNA adducts, adverse birth outcomes, developmental disabilities, clinical disease and death
![Page 67: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/67.jpg)
These changes can be…
![Page 68: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/68.jpg)
Randomised Controlled Trial
• Compares effectiveness of a new intervention against the best current alternative (or a placebo)
• Can be for clinical or behaviour change interventions
![Page 69: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/69.jpg)
Randomised Controlled Trial
• Select people with the same disease or characteristics (a defined target population)
• Randomly allocate these people to ‘intervention’ or ‘control’ groups
• Intervention group receives the new treatment, the control group receives the standard or placebo treatment
• The benefits of each treatment are assessed by comparing the health gain in each group
![Page 70: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/70.jpg)
Randomised controlled trial
population
group 1
group 2
Outcome
Outcome
intervention
control
![Page 71: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/71.jpg)
Example 11: RCT
Didgeridoo playing as alternative treatment for obstructive sleep apnoea syndrome: randomised controlled trial. Reported in BMJ Dec 2005.
•25 adults with obstructive sleep apnoea, randomised to didgeridoo instructions and daily practice for 4 months (14), or placing on the waiting list for lessons (11).
•Didgeridoo players reported less daytime sleepiness and their partners reported less night time disturbance, compared with waiting list group.
![Page 72: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/72.jpg)
In the news…..BBC website
Vitamin D ‘can lower cancer risk’High doses of vitamin D can reduce the risk of developing some common cancers by as much as 50%, US scientists claim.
Grapefruit 'may cut gum disease' Researchers found people with gum disease who ate two grapefruits a day for a fortnight showed significantly less bleeding from the gums.
Oily fish is a source of vitamin D Grapefruit is full of vitamin C
Sibling link to heart health risk Having a brother or sister with cardiovascular disease (CVD) is bad news for your own odds of developing problems, research has found.
Heart disease may run in the family
![Page 73: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/73.jpg)
Interpreting results of analytical studies
• No association found
• Association may be artifactual (false)– Due to chance – Due to bias in the study
• Association may be real, but indirect– Apparent relationship due to a confounding factor
• Association is direct (causal, true)
![Page 74: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/74.jpg)
An ASSOCIATION between a risk factor (smoking) and a disease (lung cancer)
DOES NOT INDICATE a CAUSAL relationship
Central dogma of epidemiology
![Page 75: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/75.jpg)
Association is not proof of causeBradford Hill’s Criteria for Causation
• Strength of association• Temporal relationship • Geographical distribution • Dose-response relationship • Consistency of results• Biological plausibility (but remember John Snow)• Specificity (if a single causal agent)• Reversibility
![Page 76: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/76.jpg)
Assessing the relationship between a possible cause and an outcome
A p p ly g u id e lin es an d m ake ju d g em en t
C ou ld it b e cau sa l?
C ou ld it b e a resu lt o f ch an ce?
C ou ld it b e d u e to con fou n d in g ?
C ou ld it b e d u e to se lec tion o r m easu rem en t b ias?
![Page 77: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/77.jpg)
Horses for courses
![Page 78: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/78.jpg)
Conclusions
• Epidemiology is a core part of public health.
• It allows the distribution of health and ill-health in a population to be described, and possible causal factors to be identified.
• It enables public health professionals to understand health problems and take appropriate action.
![Page 79: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/79.jpg)
What we have covered:
• What is epidemiology and what are its uses?• Descriptive epidemiology.
– Incidence and prevalence• Analytical epidemiology
– types of studies– association and causation
![Page 80: Epidemiology. 1.What is epidemiology and what are its uses? 2.Descriptive epidemiology – Incidence and prevalence – Qualitative information 3.Analytical.](https://reader030.fdocuments.in/reader030/viewer/2022032607/56649ed95503460f94be7552/html5/thumbnails/80.jpg)
References
• Medical statistics at a glance – Petrie and Sabin. Blackwell.
• Epidemiology in Medicine – Charles Hennekins. Little, Brown and Company.
• Epidemiology for the uninitiated – G.Rose and D.Barker.
• Health Knowledge website http://www.healthknowledge.org.uk/Epidemiology/Epidemiology%201.htm