What is Epidemiology?
Epidemiology is about determining whether there is a causal relationship between health exposures and health outcomes
-- First came from John Snow
-- Goal: to use study designs + epidemiology + biostats to show a CAUSAL relationship
First John Snow Study
- JS studied CHOLERA
--- The water runoff was going towards/away from the water source. He counted the number of people that got sick on each side of the street (collect DATA).
- The main theory was Miasma - disease caused from bad air
** CORRELATIONAL st
Second John Snow Study
- JS studied different water companies:
A: Southwark & Vauxhall - drinking water runs down the stream coming from the sewage. This water contains 4x more Na (salt) as the water from Lambeth
B: Lambeth - water from the sewage did not pass through here
---
Third John Snow Study
- JS measured the distance from where the person that died lived to the nearest or to the different water pumps. If the distance was the shortest, the person was more likely to walk to that water pump.
--- A lot of people were dying around Broad St.
*** C
Ignaz Semmelweis Study
- He studied hand washing after handling cadavers.
--- One clinic was run by residents and the other my midwives. He studied PUERPERAL FEVER.
*** CORRELATIONAL study
- INTERVENTION: he made doctors wash their hands with Cl - there was a decrease in people
Louis Paster Study
- LP studied if organisms can SPONTANEOUSLY be generated from microorganisms.
--- Broth is boiled into a curved neck flask - air can get in the container but the microorganisms get stuck in the curved part. Nothing grows inside. If you break the curved po
Robert Koch Study
- RK wanted to know if microorganisms were causing disease. He exposed animals to different microbes causing animals to get sick and die.
*** CAUSATION
What are Koch's Postulates?
1. Microbes must be present in organisms showing symptoms - sign of sickness
2. Microbes must be removed from the organism and grown outside its host - isolating a microbe.
3. Taking an isolated microbe and using it to infect a healthy host.
4. Isolate th
Define MORBIDITY
A diseased state. Any departure, subjective or objective, from a state of physiological or psychological well-being.
-- The rate at which an illness occurs:
the number of people who are affected within a group / the entire number of people in that group
Define MORTALITY
The ratio of actual deaths to expected deaths.
-- Number of people who died within a population
Define LIFE SPAN
- The max obtainable age of a member of a species.
- Oldest age documented.
Define LIFE EXPECTANCY
- The number of years, based on statistical averages, that a given person of a specific age, class, or other demographic variable may be expected to continue living.
- Average number of years that a person born in a particular year can expect to live.
Differentiate RATE + RATIO + PROPORTION
RATE: measure of the frequency with which an event occurs in a defined population in a defined time
*** It has a TIME dimension
-- Numerator is included in the Denominator
PROPORTION: same as rate but without the TIME dimension
-- Numerator is included in
Defines VARIABLES + types
VARIABLE: anything that has a quantity or quality that varies
1. DEPENDENT: outcome - it depends on the independent variables. --- Y axis
2. INDEPENDENT: whose value determines that of others - it represents Tx or experimental variable that is manipulated
Difference bw ASSOCIATION + CORRELATION
- ASSOCIATION: statistical relationship bw 2 or more events - may not imply cause and effect.
--- Relationship bw 2 random variables which makes them statistically dependent
- CORRELATION: the degree to which 2 or more attributes on the same group show a
Types of CORRELATION
1. Positive
2. Negative
3. No correlation
NON-CLINICAL + CLINICAL DISEASE
NON-CLINICAL (SUBCLINICAL): anatomical or physiological changes not yet sufficient to produce signs/symptoms of a disease
CLINICAL: anatomical or physiological changes sufficient to produce signs/symptoms of a disease
Types of NON-CLINICAL DISEASE
1. PRECLINICAL: not apparent yet, but disease is destined to become clinical
2. SUBCLINICAL: disease will not become clinical
3. CHRONIC: clinical symptoms persist, albeit at a low level, for a long time
4. LATENT:asymptomatic infection capable of manifes
Define ENDEMIC
Disease habitually present in a geographic area or population.
Define EPIDEMIC
An increase, often sudden, in the number of cases of a disease above what is normally expected in that population in that area.
Define OUTBREAK
Same as epidemic but in a smaller geographic area
Define PANDEMIC
Epidemic that has spread over several countries or continents
What is COMMON VEHICLE EXPOSURE?
It means that all the cases that developed were in persons exposed to the factor in question.
Define HERD IMMUNITY
The resistance of a group of people to an attack by a disease to which a large proportion of the group members are immune.
Define INCUBATION PERIOD
Interval from receipt of infection to the time of onset of clinical illness
Define ATTACK RATE
Number of people at risk in whom a certain illness develops / total # of people at risk
Differentiate DESCRIPTIVE vs INFERENTIAL STATS
DESCRIPTIVE: describe, show or summarize data in a meaningful way
--- Mean, median, mode, standard deviation, prevalence, incidence
INFERENTIAL: uses a random sample of data from a population to make inferences about that populations
--- Probability, like
Types of Data
1. Nominal (categorical) - data is just allocated to distinct categories
2. Ordinal (ranked) - data consists of numerical scores that exists on a scale.
3. Interval - equally spaced intervals
4. Discrete - order + magnitude are observed. Numbers represent
Techniques used for Summary Measurements
1. Mean - sensitive to outliers
--- Sum of values / total number of values
2. Median - even vs odd
--- Middle value of a list of data sorted from least to greatest
3. Mode - most common value. least affected by outliers.
Define RANGE
- It is a measure of dispersion
- Difference bw the largest and the smallest observation.
--- Maximum value - Minimum value.
- Very sensitive to extreme values.
Dispersion Measurement is done through ...
- Interquartile range (bw 25-75%) - to study IQ
- Variance: average of the squared differenced from the mean
- Standard deviation: square root of variance
--- Summary of dispersion around the mean
Types of Skeweness
1. Positively skewed:
--- Mode < Median < Mean
2. Negatively skewed:
--- Mean < Median < Mode
What is SURVEILLANCE + types?
It is carried out to monitor changes in the levels of risk factors.
1. Passive S: disease reporting is mandated or requested. eg. health care providers or district health officers.
2. Active S: project staff are recruited to carry out a surveillance progr
Define INCIDENCE RATE
*** # of new cases of a disease occurring in the pop during a specified period of time / # of persons who are at risk of developing the disease during that period of time
--- It is a measure of risk
Define PREVALENCE
*** # of cases of a disease present in the pop at a specified time / # of persons in the pop at that specified time
--- We do not have a measure of risk
Types of PREVALENCE
1. Point P: prevalence of the disease at a certain point in time
2. Period P: how many people have had the disease at any point during a certain time period?
Relationship bw INCIDENCE + PREVALENCE
Prevalence = Incidence * duration of the disease
Difference bw SYSTEMATIC REVIEW + META-ANALYSIS
SYSTEMATIC REVIEW: selects and assesses peer-reviewed articles in order to synthesize the literature regarding a specific health topic.
META-ANALYSIS: statistical analysis of a large collection of analysis results from individual studies for the purpose o