Stats Flashcards
Define bias
Systematic difference between the observed effect and the true effect. Not due to chance.
Define categorical data
categorical data refers to data is qualitative, describes a quality. It can either be ordinal or nominal
Define evidence based medicine
The use of the best available scientific research to guide clinical decision making
Define NNT
Number needed to treat refers to the number of patients needed to be treated with an intervention for 1 patient to have a benefit. Equals 1/ ARR
Define PPV and NPV
PPV: given the test is positve, what proppriton actually have disease= TP/ TP+ FP NPV: given that the test is negative, which porpotion don’t have disease: TN/ FN + TN
Define quantitative data
Quantitative data is numerical. It can be continuous or discrete. Continuous data can either be ratio (a zero point exists) or interval
Define relative risk reduction; absolute risk reduction
RRR= differnece between the incidence in the unexposed verus exposed / the incidnece in the unepxosed ARR: difference in the incidence between the unexposed and exposed.
Define risk ratio; define odds ratio;
risk ratio= relative risk: incidence in the exposed/ incidence in the unexposed.Used for RCT/cohort studies Odds ratio: odds of event in the exposed/ odds of the event in unexposed. Use in case control studies when can not determine incidence. Approximates relative risk, especially for rare events.
Define standard deviation; define variance
standard deviation: square root of the variance; vairance: the average of the squared differences from the mean = E (x- average x)** / (n-1)
define standard error of the mean (SEM)
SEM is the standard deviation of the sampling distribution. SEM= s/sqr(n) (sqr=square root)
Define Standardised Mortality ratio
Defined as the observed mortality rate/ expected mortality rate (as estimated from scoring systems such as APACHE II)
List non- parametric tests
Chi squared Wilcoxon Mann Whitney U test Kruskal wallis
What are the features of a normally distributed population
mean= mode= median bell shaped curve 68% of poupulation within 1 SD of mean 95% of populatio within 2 SD of mean
What are the parametric tests
t-test ANOVA
What are the Wilcoxon rank sum test, Wilcoxon paired sample test; Mann Whitney U test and Krsukal Wallis tests?
Wilcoxon rank sume test: non parametric equivalent of t test Wilcoxon paired sample test: non paramertric equivlanet of paited t test Mann Whitney U test: Non parametric equivalnet of t test Kruskal Wallist test: non parametric equivalent of ANOVA (i.e. more than 3 groups with continuous variables)
