Epi Flashcards
Primary prevention
Stop getting the disease
Eg wearing suncream
Secondary prevention
Early identification and treatment
Treat RFs
Cure / prevent progression
Tertiary prevention
Rehabilitation of people with established disease
Aims to reduce numbers/ impact of complications
When should primary prevention start
As early as possible. E.g. During or pre conception
Why cant do RCT for questions about prognosis
unethical to make them wait if there is a treatment
Sensitivity calculation
proportion of people truly positive with the disease = true positive / total
Specificity calculation
probabiluty of -ive test result in people without the disease= true -ive /tatal
How to tell whats true positive or negative
if gold standard test is positive and the new intervension is +, then true +
if gold standard test is negative and the new intervension is -, then true -
which one is good to rule things out? in? a specific or sensitive test?
SnNout Sensitivity; rules out (eg D-dimer) (if high and -, then they most likely dont have the condition)
SpPin- specific; rules in ( if high and + then they most likely have the disease)
Positive predictive value
the probability of having disease if you test positive
Negative predictive value
the probability of not having disease if you test negative
work up bias
- when gold standard test is too expensive/invasive
- so you only use it in advanced disease eg kidney biopsy
- so you may end up overestimating the sensitivity
reporting bias
was it blinded to investigators?
publication bias
difficult to publish -ive results
spectrum bias
A type of sampling bias
Pt mix in one clinic may be completely different from another
Therefore performance of a diagnostic test may be completely different
+ive likelihood ratio
LR+= Sensitivity / 1-specificity
Likelihood ratio
values close to 1 indicating no better than random
if higher than 10, it is likely and conclusive of disease presence
Intension to treat analysis
Analyse data from everyone randomised no matter whether they dropped out or not throughout the trial
Per protocol analysis
Just analyse people who completed/complied with the study protocol, exclude dropouts
Sensitivity analysis
Doing the analysis using different assumptions, eg if seeing if certain drug gives you hyponatraemia, analyse for Na < 135 mmol/L, then Na < 130, then etc.
See if lower Na levels have an effect on the outcome
Pragmatic study
Very inclusive, generalisable
Assesses real world
Explanatory RCT
Selected (exclusive) patients
Assesses best case, efficacy
Cluster randomisation
Groups rather than individuals
Advantages of cluster randomisation
Avoid performance bias (treating similar patients differently)
Avoid contamination
