Stats Flashcards
Likelihood ratio
Express a change in odds
Positive = increase in probability of disease if test is positive. Larger the +LR, more informative the test.
Negative = decrease in odds of having disease with negative results.
Smaller -LR, more informative the test
Positive predictive value
Ratio of patients truly diagnosed as positive to all those who had a positive test result:
TP = TP/(TP+FP)
Negative predictive value
Ratio of patients truly diagnosed as negative who are negative for the test
NPV = TN/(TN+FN)
Likelihood ratio calculate
LR+ = DSens/1-DSpec
LR- = 1-DSens/DSpec
Standard error of mean
Standard deviation ÷ Square root of n
Power
Measure of a studies ability to detect the smallest difference between 2 groups, considered clinically worthwhile.
Probability that a type 2 error (incorrectly accepting null hypothesis) will not be made
Power increase
Large sample size
Increase p-value
Decrease in variability of outcome measure (standard deviation)
Variance
Dispersion of values around the mean
Square of SD=variance
Sum of (difference between all values and the mean) squared÷ n-1
Standard deviation
A statistical measure of the degree of data spread about the mean
SD = square root of variance
Standard deviation in normal distribution
1 SD from the mean, 68% of observations
2 SD from the mean, 95% of observations
3 SD from the mean, 99.7% of observations
Standard error of the mean
Standard deviation ÷ Square root of n
Confidence level
1-alpha
Ability to reject alternate hypothesis correctly as there is no effect
Type 1 error
Alpha
Failure to reject null hypothesis, e.g. saying there is a difference when there isn’t
False positive
Caused by multiple testing
Power
1-beta
To find true effect
Beta
Type 2 error
Incorrectly accepting null hypothesis, saying no difference when there is
False negative
