PP

Definitions

Standard deviation

  • Amount of variation from the mean value

Standard Error

  • Standard deviation of means from multiple samples
  • No sample fully representative
  • STANDARD ERROR: measure of deviation of sample's mean from true popn mean
  • Higher sample sizes reduce SE

Correlation Coefficient

  • Strength of pattern

Regression coefficient

  • Describes the pattern
  • PREDICTS, DESCRIBES, ADJUSTS

Definitions

Prevalence

  • Number of existing cases

Incidence

  • Number of new cases

Study Hierachy

Stronger methodology, Less Bias, Controls for comparison, Fewer studies

  • Meta-analysis
  • Systematic reviews

Randomized controlled trials

  • One intervention group, one control group
  • Participants truly randomised to one of two groups
  • Blinding to remove bias
  • Best but expensive

Cohort studies

  • Longitudinal, prospective study
  • Starts before disease onset
  • Two groups: exposed to risk factor and not exposed
  • Groups are followed and incidence of disease is monitored
  • Produces relative risk
  • Expensive and time consuming
  • Observer bias but reduced recall and selection bias

Case control Studies

  • Exposure to risk factor assessed in group of cases (people with disease) compared to a group of controls (people without disease)
  • Matching is employed as control of confounding risk factors
  • Only proves association, not causation
  • Produces an odds ratio
  • Recall and selection bias

Case reports/ Case series

  • Individual case
  • Number of same/similar case

Animal and lab research

Correlation study:

  • Correlates two or more variables to investigate relationship

Cross Sectional Study

  • (Prevalence study): snap shot of popn, good indicator of prevalence

Definitions

Relative risk

  • Risk of disease in exposed relative to unexposed. Expresses how many more times likely even is to occur in one group compared to another
  • Thing over total

Absolute risk

  • Probability of event occuring

Defintion

Odds Ratio

  • Product of case-control
  • Odds of event occuring in one group compared to odds of another
  • Thing over other thing
  • If odds ratio >1, there may be an association between risk factor and event
  • <1, factor may be protective against event
  • = 1 factor makes no difference

P values

  • Measure of statistical significance
  • Probability than an effect is not due to chance alone
  • p<0.01: very strong presumption against null hypothesis
  • p<0.05: Strong presumption against null hypothesis

Null Hypothesis

  • Opposite to what you are testing

Type 1 error

  • Null hypothesis incorrectly rejected:OPTIMIST

Type 2 error

  • Null hypothesis incorrectly accepted: PESSIMIST

Definitions

Accuracy (validity)

  • How good a test is at identifying correct answer

Reliabilty (consistency)

  • How consistent a test is

Bradford Hill Criteria

Does association conform with current knowledge

If study was replicated in different time + place, same association?

How strong is the association between cause and effect (relative risk)

Evidence from strong study?

If exposure to cause goes up, does effect follow/vice versa if considering treatments

Single cause produces specific effect

Applying accepted evidence another area of study

Does the cause come before the effect?

TEMPORALITY

If the cause is removed, does the effect go away?

REVERSIBILITY

DOSE RESPONSE RELATIONSHIP/BIOLOGICAL GRADIENT

STRENGTH

PLAUSIBILITY

CONSISTENCY

STUDY DESIGN

SPECIFICITY

ANALOGY

Maxwell Criteria

How is service views

Fairness (not equality). People treated regards to their needs

Is service relevant to needs of popn?

Cost effective?

Does service have access for service users?
Are appointments at accessible time?

How well does it work?

ACCESIBILITY

APPROPRIATENESS

ACCEPTABILITY

EFFECTIVENESS

EFFICIENCY

EQUITY

Wilson-Junger Criteria

  • Criteria should be applied before implementing potential popn screening programme
  • Is condition an important health problem?
  • Is there suitable exam/test?
  • Is there accepted/effective treatment?
  • Diagnostic and treatment facilities available?
  • Disease have latent/early symptomatic stage?
  • Natural record of condition known?
  • Agreed policy on who is case + treatment
  • Economically viable?
  • Continuing process?

Suitable test/exam


False positive

  • People identified as having disease, further tests they do not

True positive

  • People identified as having disease, further tests confirmed

False negatives

  • People identified as not having disease, further tests they do

True negatives

  • People identified as not having disease, further test confirms

Sensitivity and specificity: Measures of accuracy of screening test
Sensitivity: True +ves/ (True +ves + False -ves)

  • Everyone that has disease

Specificity: True -ves/ (True -ves + False +ves)

  • Everyone that doesn't have disease

PPV: positive predicitive values

  • The chance, if you test +ve, you will have disease

NPV: Negative predictive values

  • The chance, if you test -ive, that you will not have disease