EBM Flashcards
What p value would cause one to accept the null hypothesis of a chi-squared analysis?
p > 0.05
When would linear regression be used?
To help predict a variable from another variable
So you draw out a line chart and use one value to predict the other
When would an un-paired t-test be used?
To compare the means of two unrelated populations
When would a paired t-test be used?
To compare the means of two related populations (e.g. the same population before and after)
What is a meta-analysis?
Combining results from different studies
What is sensitivity?
Measures the proportion of +ve’s identified (e.g % of sick people identified as sick).
TRUE POSITIVE RATE
What is specificity?
Measure the proportion of -ve’s identified (e.g. % of healthy people correctly identified as not sick).
TRUE NEGATIVE RATE
The most important 3 factors when assessing a clinical trial are…
Validity, results and clinical relevance
When would you use regression and what are the two types?
To predict dependant variable from independant
Can correct for confunding variables
Linear- when continous outcomes
Logistic- When binary outcomes
What is the t-test used for?
Tests the change in mean between two groups
CONTINUOUS VARIABLE
What is the chi-squared test used for?
Version of t-test to see if expected freq = anticipated frequency (testing null hypothesis)
BINARY VARIABLES ONLY
What equation is used to calculate odds ?
Number of individuals without outcome
What equation is used to calculate odds ratio?
odds of the outcome in another group (e.g. control)
What is implied by an odds ratio of 1?
No difference between the two groups
What is used to test the significance of odds ratio’s?
Chi squared
Allows us to compare proportions across two different groups.
Tells us whether the comparison is statistically significant (it gives a p value).
What is Multiple (or multivariate) logistic regression used for?
Used to assess the predictive value of one or more variables on a YES/NO outcome
You are asked: “How does smoking affect the likelihood of having pancreatitis, after accounting for (or ‘unconfounded by’ or ‘independent of’) alcohol consumption, BMI, etc.?”. What do you use to find the answer?
Multiple logistic regression
What is positive predictive value?
Probability that the disease is present when the test is positive.
What is negative predictive value?
Probability that the disease is not present when the test is negative.
What equation is used to work out positive predictive value?
(true positives + false positives)
What equation is used to work out negative predictive value?
(true negatives + false negatives)
The true positive rate is also known as…..?
Sensitivity
False positive rate is also known as….
(1- Specificity)
What is found on the x and y axis of ROC curves?
x axis = (1- specificity)
y axis= Sensitivity
What does ROC stand for?
Receiver Operating Characteristic
What are ROC curves used for in a clinical context?
Setting test cut off points
What does the null hypothesis usually state?
That the difference between the two means is 0
so intervention makes no difference
What p value would cause you to reject the null hypothesis?
p less than 0.05
What is a categorical variable?
Can take a fixed number of values
What is a discrete variable?
Can take any of a number of values
