BCPP Biostatistics Review Questions with Complete Solutions

Descriptive Statistics Tendency = mean, median, mode. Variaibility = variance, standard deviation, interquartile range. " Inferential Statistics Conclusions based on rules of probability. Used to compare investigational medication to control treatment. Minimizes investigator bias. Variables Dependent - outcome of interest. Independent - variable used to predict the value of the dependent variable. Ex. Independent variable new medication, Dependendent variable HAM-D score" Continuous Data Defined units, equal distance between increments. Interval zero point arbitrary (deg F. ) Ratio absolute zero - blood pressure, blood glucose, triglycerides. " Discrete Data Nominal names, categories (eye color, religion, sex blood type presence of absence of disease) Ordinal order of rank - cancer staging, heart failure class" Mean sum of all data points divided by the number of data points. Continuous data. Extremely sensitive to outliers Median Value above or below which half of the data points fall. 50th percentile. Not sensitive to outliers. Useful when outliers present of continuous data not nl distribution. Cont or Ordinal data Mode Most commonly observed value in distribution. Describes nominal, ordinal or continuous data. May be more than one - bimodal" Variance Measure of degree to which data are scattered around the mean/median. Mean of the squared differences of the observed values from their mean. Standard Deviation (SD) Most common, measures spread, meaningful only in nl or near nl continuous distribution. Computed by square root of variance. 68% within 1 SD, 95% within 2SD, 99.7% within 3SD. " Standard Error of the Mean (SEM) Quantifies the uncertainty in the estimate of the mean.Computed from SD SEM= SD divided by the square root of n (n=number of subjects) Always smaller than SD unless = 1. Decreases as sample size increases, increases as SD increases. "