Statistics

Question 1

Sensitivity

Answer 1

the proportion of people who test positive among all those who actually have the disease

Question 2

Specificity

Answer 2

the proportion of people who test negative among all those who actually do not have that disease

Question 3

PPV

Answer 3

the probability that, following a positive test result, that individual will truly have that specific disease

Question 4

NPV

Answer 4

the probability that, following a negative test result, that individual will not have that specific disease

Question 5

As prevalence decreases, what happens to a) PPV and b) NPV

Answer 5

a) PPV decreases - there will be more false positives for every true positive “needle in a haystack”

b) NPV increases - more true negatives for every false negative
- bc a false negative would mean the person actually has the disease, which is unlikely because the disease is rare (low prevalence)

Question 6

Correlation

Answer 6

statistical measure which determines co-relationship or association of two quantitative variables

used to represent a linear relationship between two variables

Question 7

Regression

Answer 7

describes how an independent variable is numerically related to the dependent variable. used to estimate a line of best fit and estimate one variable on the basis of another

can make predictions about what we expect among individuals who have not had the dependent variable measured

Question 8

Statistical inference

Answer 8

Statistical inference is the process of using data analysis to deduce properties of an underlying probability distribution

Question 9

Adjusted R sq

Answer 9

estimates the total proportion of overall variation of ___ explained by the fitted regression model

Question 10

R sq

Answer 10

___ % of the variability in variable Y is explained by variation in X

Question 11

Coefficient

Answer 11

For every one unit change in X, there is a coefficient (beta) unit change in Y

Question 12

cox proportional hazard model

Answer 12

allows for survival times to be modelled in terms of continuous and categorical explanatory variables

any factor alters the hazard factor at the same magnitude at all time points

Question 13

Hazard ratio

Answer 13

the probability of an individual dying at time (t) compared to background hazard rate in people without intervention

Question 14

Bland Altman Plot

Answer 14

graphical method to compare two measurement techniques

plots the difference between measurements for each data point against average of observations

Question 15

Number needed to treat NNT

Answer 15

the number of patients you would need to treat with new treatment to have ONE MORE SUCCESS than with the old treatment

Question 16

Parametric

Answer 16

assumes variables have been sampled from a normal distribution (as defined by mean and SD)

Question 17

H0 of mann whitney and equivalent

Answer 17

H0: both groups observations are sampled from the same underlying distribution

2 sample t

Question 18

H0 of wilcoxon signed ranks and equivalent

Answer 18

H0: pops MEDIAN is of a particular value

one sample t

Question 19

H0 of wilcoxon matched pairs test and equivalent

Answer 19

HO: median difference in popn is 0 - values of 1st measurement are apron equal to those of the 2nd measurement

paired t test

Question 20

kruskal wallis test

Answer 20

ANOVA

h0 all groups come from popns with same distribution

Question 21

Assumption of MW CI

Answer 21

that the two groups have the same shape and spread (differ only in medians not variability)

Question 22

I squared

Answer 22

measures the percentage of variability in treatment effect estimates that is due to between study heterogeneity rather than chance

Question 23

P value

Answer 23

the probability of obtaining the observed data or data more extreme, assuming the null hypothesis is true eg. 5% chance if null is true

due to random sampling error

Question 24

censored observation

Answer 24

information about an individuals survival time is incomplete - shows time spent in study before an indivudal left due to unrelated illness/condition, drop out etc

Question 25

Log rank test

Answer 25

tests for differences in survival times. goodness of fit

NPM

Question 26

ROC curve

Answer 26

plots sensitivity v 1- specificity for different cut off points

helps define cut off point for a test with continuous measurements