Interpreting Data Flashcards
How do we calculate standard deviation (SD)?
square root of variance
How do we calculate standard error of the mean (SEM)?
standard deviation / square root of sample size
Within a normal distribution, what percentage of values lie within +/- 1 standard deviation from the mean?
68%
Within a normal distribution, what percentage of values lie within +/- 2 standard deviations from the mean?
95%
What is meant by the measure of central value?
Another way of saying median
How do we calculate a confidence interval?
Sample mean +/- 1.96 SE
sometimes 2 SE is used instead for simplicity
What is meant by a Type 1 Error?
False positive
Incorrect rejection of null hypothesis
What is meant by a Type 2 Error?
False negative
Incorrect acceptance of null hypothesis
What are the effects of increasing the sample size?
Decreases type 2 error and increases power of study
What are the axes of a ROC curve?
Sensitivity vs (1-Specificity)
How do we calculate number needed to treat (NNT)?
1/(ARR = absolute risk reduction)
What is meant by the power of a study?
The study’s ability to detect an effect of a specified size
What is meant by a likelihood ratio?
The effectiveness of a particular diagnostic test to confirm or exclude a particular diagnosis
How do we calculate a positive likelihood ratio?
Sensitivity/(1-specificity)
What is the best way of representing the probability of survival in a graphical form?
A Kaplan-Meier plot
