CRQ Flashcards
Hierarchy of evidence
Meta analysis Rct Non randomised CT Cohort study Case control study Cross sectional surgery Case series Case report
Sensitivity
Chance of it being correctly positive
Ie does have the disease and is positive on the test
A/ a+c
Positive predictive value
If positive on a test what is the chance they actually are positive for the disease?
A/a+b
Specificity
If they don’t have the disease what is the chance the test correctly identifies them as negative?
D/b+d
Negative predictive value
If the patient is negative on the test what is the chance they actually are a true negative without the disease
D/c+d
What does CONSORT diagram stand for?
Consolidated standards of reporting trials
To improve quality of rct
Patient flow
Includes those lost to follow up
Evidence based minimum set of recommendations for reporting rcts
Standardised way to present report findings
What does PICO stand for?
Formulating a question for a study
Patient or problem (population)
Intervention
Comparison
Outcome
Case report
Experience of one person
Anecdotal
Prone to chance and bias
Case series
Group of people studied
Useful for rare diseases
5 children who presented to EF with abdo epilepsy etc
Cohort study
Consequences of exposure to a risk factor
Same group of people followed
One with risk exposure and one without
No one has the disease at start of the trial
Can do retrospectively
Takes long time (usually years)
E.g 500 people who smoke cannabis monitored for 15 years to see if at greater risk of developing schizophrenia
Case control study
Compares those with disease and those without
and looks at a risk factor
50 women with hepatitis and 50 women without queries about ear piercing to see if a risk factor
Cross sectional study
Surveyed group of people at one point in time
Prevalence of exposure and outcome in a population
E.g population questionnaire examining prevalence of stroke risk factors
RCT
Minimises bias
Measures efficacy
Compare two treatments
Kids with fever given either paracetamol or ibuprofen to determine which is better at reducing fever
Endpoints
Study should say how endpoint selected e.g morbidity, plaque developed, major CV risk factor
Validity
How well does it measure what it was supposed to
Measures variable
Criteria compared to what is know to be valid
Reliability
How consistent a test is on repeated measurement
How true is it to true value
Consistency of measurement
Measurement error either:
systematic (dif readings on same machine)
Random error- dif in weight readings
Incidence
Rate of occurrence of new cases over a period of time
Measures risk of disease
Number of new cases over time period divided by population size
Prevalence
Proportion with disease at a given time
Number with disease divided by population size
Variance
Sum of all the differences between the values plus the mean squared
Divided by
Total number of observations - 1
( work out mean Minus mean from each value Square each result Sum of squared results Divide by number of results -1
Standard deviation
Degree of spread from the mean
Square root of variance
2 standard deviations above and below =95%
Z score
Value of an observation into number of standard deviations frommean where it lies
Observation -mean divided by standard deviation
95% confidence interval
95% of means in the sample like in 1.96 standard error
So 95% of the time the population mean would lie in this range
Equation for risk
Number of times an event likely to occur
Divided by
Total number of events possible
Ie one in 6 fall ill
Risk = 1/6 = 0.167 or 16.7%
Equation for odds
Ratio of number of times likely to occur
Divided by number of times not likely to occur
1/5 = 0.2 odds of falling ill
