Lecture 3 - Measurements Flashcards
What is Descriptive epidemiology?
When the burden of a disease is measured
How frequently does it occur?
How quickly does it occur?
What is analytical epidemiology?
Measures the causes and effects
How and why does it occur
What is incidence?
The number of new cases within a given period of time
What is prevalence?
The number of existing cases within a given period of time
What is the equation for incidence risk?
Num of new cases in a certain time / size of case freee population at start of period
What is the incidence rate equation?
Num of new cases during a certain time / the time each person was observed totalled for all people
What is the prevalence rate equation?
All new and pre-existing cases durin a given time period / population during same time period
What actually is incidence rate?
How quickly a disease occurs in a population not a proportion
What is the difference between incidence and prevalence?
Incidence only involves NEW cases
Prevalence involves BOTH pre existing and NEW cases
What should the Incidence risk and prevalence rate be like for Short lived diseases?
Incidence risk and prevalence rate should be SIMILAR
What is Case-fatality rate?
The incidence risk of a specific cause
E.g num of patients died of influenza
What is mortality rate?
Incidence rate all or specific. Cause
E.g number of people who die in a year per 100,000 of population
How is incidence risk clinically relevant?
If u think a patient may have 1 of 2 diseases you’d order the test with the higher incidence risk
How can incidence risk be used to see if theres a relationship between smoking and lung cancer?
Have 2 groups of people :
Smokers + Non smokers
Will find that the incidence risk of lung cancer in smokers is higher than in the non smokers
When a study is done on 2 groups of people where 1 group given antivirals and the others no antivirals to see if an antiviral is effective in reducing mortality.
What is the cause and what is the effect?
Cause = antiviral
Effect == death due to viral infection
What is Risk ration and odds ratio use to measure?
QUaitfy the strength of association between the exposure and event
What are 3 potential cause and effect isssues that can falsify the finding?
Confounding
Chance
Bias
What is a confounder?
Other factors which are associated witht the exposure and outcome which aren’t considered which may falsify findings
How can chance falsify a finding?
The observed association may happen by chance (random error)
How can bias affect/falsify findings?
There may be errors in the data collection, analysis and interpretation that lead to results that are systematically different from the truth
How does increasing the sample size help decrease chance falsifying findings?
The larger the sample the more closely the sample reflects the whole population so any odds ratios calculated are more likely to match the population
What is selection bias?
When the sample is not representative of the population
When many individuals have been sampled in a study and they have the lung cancer gene, what type of bias is this?
Selection bias
What is confounding bias?
The effect of exposure on outcome is mixed with another factor
What type of bias is this?
Age of individuals are not taken into account when calculation odds ratio?
Confounding bias
What is recall bias?
Incomplete/inaccurate recollection of info by participants
(Can’t remember if they smoked or said the wrong answer)
What type of error does bias cause?
Systematic error
What type of error does bias cause?
Systematic error
What type of association is indicated by an odds ratio or Risk ratio being equal to 1?
When OR or RR = 1
NO ASSOCIATION BETWEEN EFFECT AND OUTCOME
What type of association is indicated by an odds ratio or Risk ratio being less than 1?
OR or RR less than 1 = NEGATIVE ASSOCIATION BETWEEN EFFECT AND OUTCOME
What type of association is indicated by an odds ratio or Risk ratio being more than 1?
OR or RR more than 1 = POSITIVE ASSOCIATION BETWEEN EFFECT AND OUTCOME
How would you work out the Risk Ratio (RR) for people who are smokers getting lung cancer to non smokers getting cancer?
Do num smokers with lung cancer DIVIDED by TOTAL num of smokers (say value obtained is x)
Do num of Non smokers with lung cancer DIVIDED by TOTAL num of non smokers (say value obtained is y)
Then do x DIVIDED by y to get the RR
How would you work out the Odds Ratio (RR) for people who are smokers getting lung cancer to non smokers getting cancer?
Do num of smokers with lung cancer DIVIDED by num of smokers WITHOUT lung cancer (say this value is x)
Do num of non smokers with lung cancer DIVIDED by num of non smokers WITHOUT lung cancer (say this value is y)
Then do x / y to find odds of having lung cancer compared to non smokers
What value is not used to calculate odds ratio?
TOTALS ARE NOT USED
