Term

Definition
 discrete (dichotomous, categorical)
 continuous



Term

Definition
 Nominal
 Ordinal
can only take a limited number of values within a given range 


Term

Definition
Discrete variable
Classified into groups in an unordered manner & with no indication of relative severity (sex, mortality, disease state) 


Term

Definition
discrete variable
 ranked in specific order
 no consistent level of magnitude of difference between ranks (NYHA functional class describes the functional status of pts w/heart failure & subjects classified in increasing order of disability I, II, III, IV)
 means & SD should not be used with ordinal data in most cases (measure of central tendency)



Term

Definition
Ranked in a specific order with a consistent change in magnitude between units
Zero point is arbitrary (e.g. Fahrenheit)
Continuous variable 


Term

Definition
 Can take on any value within a given range
 Sometimes referred to as Counting Variable



Term

Definition
Data ranked in a specific order with a consistnet change in magnitude between units
Has an absolute zero (e.g. degrees Kelvin, pulse, BP, time, distance)
Continuous variable 


Term
Measures of Central Tendency (3) 

Definition
 Mean
 Median
 Mode
Presenting dat using only measures of central tendency can be misleading without some idea of data spread 


Term

Definition
 Average
 Measure of central tendency
 Sum of all values divided by the total number of values
 Generally used only for continuous & normally distributed data
 Very sensitive to outliers & tend toward the tail which has the outliers
Geometric mean 


Term

Definition
 Measure of central tendency
 Midpoint of the values when placed in order from highest to lowest
 half of the observations are above & half below
 Also called the 50th percentile
 Can be used for ordinal or continuous data
 especially good for skewed populations
 Insensitive to outliers



Term

Definition
 Most common value in a distribution
 Measure of central tendency
 can be used for nominal, ordinal or continuous data
 Can be more than 1 mode: bimodal & trimodal
 Does not help describe meaningful distributions with a large range of calues, each of which occur infrequently



Term
Measures of Data Spread or variability (3) 

Definition
 Standard deviation
 Range
 Percentiles



Term

Definition
 Meaure or the variability about the mean (most common measure used to describe this)
 Square root of the variance (average squared difference of each observation from the mean) returns variance back into original units (nonsquared)
 apply only to continuous data normally or nearnormally distributed
 68% within 1 SD
 95% within 2 SD
 99% within 3 SD



Term

Definition
relates the mean & SD
SD/mean x 100% 


Term

Definition
 Difference between the smallest and largest values
 does not give a tremendous amount of info by itself
 Easy to compute (simpel subtraction)
 Size of range is very sensitive to outliers
 Often reported as the actual values rather than the difference between the 2 extreme values



Term

Definition
 The point (value) in a distribution in which a value is larger than some % of the other values in the sample
 75^{th} percentile (75% of the values are smaller)
 Does not assume the population has a normal distribution
 IQR: middle 50%  encompasses the 25^{th} to the 75^{th} percentile



Term

Definition
Discrete
Normal (Gaussian) 


Term
Normal (Gaussian) Distribution 

Definition
 Most common model for population distribution
 Symetric or "bellshaped" frequency distribution
 median and mean will be approx. equal
 Frequency ditribution & histograms (visual check look symmetrical & bellshaped)
 formal test: KolmogorovSmirnov
Landmarks for continuous, normally distributed data
 m: population mean is equal to zero
 s: population SD is equal to 1
 x and s represent the smple mean and SD



Term

Definition
 quantifies uncertainty in the estimate of the mean NOT variability in the sample
 estimates the SD of the means



Term

Definition
 95% CI most common
 gives and idea of the magnitude of the difference between groups as well as statistical significance
 if CI contains 0 = no difference between 2 variables (interpreted as not statistically significant: a pvalue _{>/=} 0.05)
 no need to show both 95% CI & pvalue
odds ratio & relative risk:
value of 1 indicates no difference in risk, no statisical difference 


Term
H_{o }(Null Hypothesis)
(rejected or not rejected) 

Definition
no difference between groups being compared
(treatment A = treatment B)
 if rejected: statistical significance between groups (unlikely attributable to chance)
 if accepted (not rejected): no statistically significant difference between groups (any apparent differences may be attributable to chance) not concluding that they are equal



Term
H_{a }(alternative hypothesis) 

Definition
 opposite of null hypothesis
 States that there is a difference between groups



Term
Parametric Tests
Assumptions
Examples (3) 

Definition
 Assume: data normal or near normal distribution  evaluate whether this is true by comparing mean to median
 data is continuous
 measured on an interval or ratio scale
Examples:
student ttest:::
onesample test: compares mean of the study with population mean
twosample test: compares means of 2 independent samples
(may not use multiple ttests with more than2 groups)
Paired test:::
compares the mean difference of paired or matched samples 


Term
Parametric tests
analysis of variance 

Definition
 Oneway ANOVA: compares means of 3 or more groups
 Twoway ANOVA: additional factor (e.g. age) added
 RepeatedMeaures ANOVA: a related samples test



Term

Definition
 may also be used for ordinal & continuous data that do not meet the assumptions of the ttests or ANOVA
Tests:
 Wilcoson rank sum & MannWhitney Utest, compares 2 independent samples (related to a ttest)
 KruskalWallis oneway ANOVA by ranks, compares 3 or more independent groups (related to a oneway ANOVA)   post hoc testing



Term
Nonparametric Tests
(tests for related or paired samples) 

Definition
 Sign test & Wilcoson signed rank test: compares 2 matched or paired samples
 Firedman ANOVA by ranks: compares 3 or more matched/paired groups



Term

Definition
Chisquare (x^{2}) test: compares expected & observed proportions between 2 or more groups:
 test of independence
 test of goodness of fit
Fisher exact test: specialized version of chisquare test for small groups (cells) containing < 5 observations
McNemar: paired samples
MantelHaenszel: controls for the influence of confounders



Term

Definition
H_{o }is rejected, when it should not have been
 conclude that there is a statistically significant difference when actually one does not exist
termed a  convention is to set it at 0.05 (5%)



Term

Definition
H_{o} is not rejected, but should have been
 concluding that no differnce exists when one truly does
termed b  conventionally set 0.20 to 0.10 


Term

Definition


Term

Definition
1b
 the probability of making a corret decision when H_{o} is false
 the ability to detect differences between groups if 1 actually exists
Dependent on:
predetermined a: the risk of error you will tolerate when rejecting H_{o}
 sample size
 the size of the difference between the outcomes wanting to detect
 variability of the outcomes being measured 

