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what is association?

association is a link relationship or correlation

it is the statistical dependence between two variables
to the degree to which the rate of disease in persons with a specific exposure is either higher or lower than the rate of disease without exposure


what is the odds ratio

odds of exposure in cases / odds of exposure in controls


what things cause association?

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what is chance?
how to check if it is chance?

calculate confidence intervals
increase the sample size


what is bias?

systematic error leading to an incorrect estimate of the effect of an exposure on the development of a disease or outcome.

Defects in design cannot be overcome by increasing the sample size


what are the two types of bias?

measurement bias
systematic error with the measurement technique
increasing sample size makes no difference
selection bias
this is when the people chosen for the study are characteristically biased


what is confounding?

this is any factor which is believed to have a real effect on the risk of a disease
can include causal factors
or more direct unknown factors


what are the stages at which the control might be founded?

- design
- analysis
regression analysis


list the hierarchy of evidence in study design:

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systematic review
cohort studies
case control studies
ecological studies
descriptive studies
case reports


what is the bradford hill criteria?

a group of minimal conditions needed to provide adequate evidence of a causal relationship between incidence and possible consequences


what is the bradford hill criteria?

– a group of minimal conditions needed to provide adequate evidence of a causal relationship between incidence and possible consequence


what must the relationship be if it agrees with bradford hill criteria?

- must be temporal


what might the relationship be if it agrees with the bradford hill criteria?

- strength of effect
- consistent with other investigations
- specificity (one risk one disease)
- a biological gradient
- plausibility (means it is consistent with other knowledge)
- coherence with current thinking and previous experiments
- experimental evidence
- an analogy
- reversibility

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what is epidemiology?

the study of the distribution of health related states or events and the determinants of health relates states or events in specified populations

also the application of this study to control health problems


what is homeopathy?

- based on principle of like cures like
- uses toxin that causes similar symptoms to the disease
- only 50% of cures effective


what is a confidence interval?

- this is the range within which the value is expected to lie within given a degree of certainty - 95%


what is a P value?

- the probability that results are simply due to chance
. p < 0.05 = 95% certain results not due to chance


what is bias?

cannot be controlled by analysis/ sample size
- measurement bias
- selection bias


what is the MMR vaccine?

this combines measles mumps and rubella
- 2 stages
prevents deaths from mumps which causes meningitis
the rubella vaccine stops kids catching rubella from their mothers


why was the MMR vaccine taken away?

- studies based on the MMR vaccine made people believe that side effects like autism were caused by the vaccine
- there was no causal link
- the MMR vaccine was taken away
- deaths went up
- returned due to recognition of the flawed causality


what is human generation time?

- this is the time taken from our birth to a female producing a child
around 25+ years for humans

- much lower for viruses and bacteria


what are the origins of human infection?

- ancestors
- wildlife
- livestock


what are changes in the world leading to spread of infectious disease?

- increasing population
more dense faster transmission of disease
increase in rate of evolution

- movement of people by planes
influenza H1N1 spread like this
due to migration of people


what is epidemiology?

- based on ability to quantify the occurrence of disease in populations
- needs definition of word case:
- case = person with disease, heath disorder, or suffering from event of interest


what is prevalence

frequency of disease in a population at a point in time

number of cases / number of people in the population

measures the burden of a disease


what is incidence?

the number of new cases of a disease within a specified time interval

Incidence measures NEW CASES while prevalence measures ALL CASES

prevalence is dependent upon incidence


how to estimate incidence ?

- define the time period
- define the denominator (how many people are at risk)
- come up with a good test to define a true case
(eg. blood test for ebola)


how does incidence influence policy makers

- it affects if the country says there is an outbreak or not


what is mortality?

mortality is the number of deaths from a specify disease or condition

if mortality = incidence
then the epidemic is stable


what is the mortality equation

deaths from disease in time period / population at beginning of start of time period