BCPP Biostatistics || 100% Correct Solutions.
Descriptive Statistics correct answers Tendency = mean, median, mode. Variaibility = variance,
standard deviation, interquartile range. "
Inferential Statistics correct answers Conclusions based on rules of probability. Used to compare
investigational medication to control treatment. Minimizes investigator bias.
Variables correct answers 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 correct answers Defined units, equal distance between increments. Interval zero
point arbitrary (deg F. ) Ratio absolute zero - blood pressure, blood glucose, triglycerides. "
Discrete Data correct answers Nominal names, categories (eye color, religion, sex blood type
presence of absence of disease) Ordinal order of rank - cancer staging, heart failure class"
Mean correct answers sum of all data points divided by the number of data points. Continuous
data. Extremely sensitive to outliers
Median correct answers 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 correct answers Most commonly observed value in distribution. Describes nominal,
ordinal or continuous data. May be more than one - bimodal"
Variance correct answers 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) correct answers 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) correct answers 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. "
SEM vs. SD correct answers Some report findings as a point estimate +/_ SEM, rather than +/_
SD. makes data appear to have less variation. "
Range and Interquartile range. correct answers Range-difference between largest and smallest
value. outliers big impact. Interquartile range measure of variability related to median between
, 25th and 75th %ile. Describes variability for ordinal data. Defines where 50% of measures occur,
spread"
Distributions correct answers Demonstrates # of times particular measurement obtained. Nl =
Gaussian (bell shaped) mean=median=mode
Skewness correct answers Mean and median pulled in direction of longer tail. Mean is pulled
farther than median. Tail may contain outliers.
Kurtosis correct answers Measure of whether data are flat or peaked. Normal (mesokurtic) dist =
3.High peak (leptokurtic) >3, Flat peak(platykurtic) <3. Higher peak = small # of extreme
differences from mean. "
Hypothesis Testing. correct answers (Ho) No difference between treatments. (H1) difference
between treatments. Ability to reject Ho is dependent on statistical analysis
Descriptive/Cross Sectional correct answers Experience or Observation. May be only available
e.g. toxicity. looks for relationships between characteristics and outcomes at point in time. case
reports, case series, surveys. Insufficient evidence, multiple bias (observer, selection,
classification)"
"Case Control (observational, comparison groups)" correct answers Retrospective, identify
outcome, then cases, then controls. Cases,controls may be matched for similarties. Good rare
disease, long latency. Examines risk factors. Weaker than cohort or randomized. Selection,
informational, recall classification bias."
"Cohort (observational, comparison groups)" correct answers Retro or prospective. Excludes
cases w/ outcome , classifies based on risk, follows longitudinally, strongest observational for
cause & effect, temporality, calc incidence. Neg-$$, long time, loss to f/u, confounding, Select,
classify, attrition bias, HE"
(HE) correct answers Hawthorne Effect - cohort - did participants change behavior due to
observation.
"Controlled Clinical Trial (experimental, comparison groups)" correct answers Gold standard.
assignment, intervention, outcome. (X-over, wash out, other tx) cause and effect, stratification,
randomization, most difficult & expensive. Not good for rare dx, selection, allocation, observers.
Need for identical tx. "
Randomizaton correct answers sample = chance of selection for study, allocation=chance for
each group, nonrandom allocation =group assigned preferentially, biases results. removes
selection bias, best w/lg group. "
Simple Random Allocation correct answers coin toss, groups may be unequal in size at any
point, difficult to detect true difference. "
Descriptive Statistics correct answers Tendency = mean, median, mode. Variaibility = variance,
standard deviation, interquartile range. "
Inferential Statistics correct answers Conclusions based on rules of probability. Used to compare
investigational medication to control treatment. Minimizes investigator bias.
Variables correct answers 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 correct answers Defined units, equal distance between increments. Interval zero
point arbitrary (deg F. ) Ratio absolute zero - blood pressure, blood glucose, triglycerides. "
Discrete Data correct answers Nominal names, categories (eye color, religion, sex blood type
presence of absence of disease) Ordinal order of rank - cancer staging, heart failure class"
Mean correct answers sum of all data points divided by the number of data points. Continuous
data. Extremely sensitive to outliers
Median correct answers 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 correct answers Most commonly observed value in distribution. Describes nominal,
ordinal or continuous data. May be more than one - bimodal"
Variance correct answers 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) correct answers 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) correct answers 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. "
SEM vs. SD correct answers Some report findings as a point estimate +/_ SEM, rather than +/_
SD. makes data appear to have less variation. "
Range and Interquartile range. correct answers Range-difference between largest and smallest
value. outliers big impact. Interquartile range measure of variability related to median between
, 25th and 75th %ile. Describes variability for ordinal data. Defines where 50% of measures occur,
spread"
Distributions correct answers Demonstrates # of times particular measurement obtained. Nl =
Gaussian (bell shaped) mean=median=mode
Skewness correct answers Mean and median pulled in direction of longer tail. Mean is pulled
farther than median. Tail may contain outliers.
Kurtosis correct answers Measure of whether data are flat or peaked. Normal (mesokurtic) dist =
3.High peak (leptokurtic) >3, Flat peak(platykurtic) <3. Higher peak = small # of extreme
differences from mean. "
Hypothesis Testing. correct answers (Ho) No difference between treatments. (H1) difference
between treatments. Ability to reject Ho is dependent on statistical analysis
Descriptive/Cross Sectional correct answers Experience or Observation. May be only available
e.g. toxicity. looks for relationships between characteristics and outcomes at point in time. case
reports, case series, surveys. Insufficient evidence, multiple bias (observer, selection,
classification)"
"Case Control (observational, comparison groups)" correct answers Retrospective, identify
outcome, then cases, then controls. Cases,controls may be matched for similarties. Good rare
disease, long latency. Examines risk factors. Weaker than cohort or randomized. Selection,
informational, recall classification bias."
"Cohort (observational, comparison groups)" correct answers Retro or prospective. Excludes
cases w/ outcome , classifies based on risk, follows longitudinally, strongest observational for
cause & effect, temporality, calc incidence. Neg-$$, long time, loss to f/u, confounding, Select,
classify, attrition bias, HE"
(HE) correct answers Hawthorne Effect - cohort - did participants change behavior due to
observation.
"Controlled Clinical Trial (experimental, comparison groups)" correct answers Gold standard.
assignment, intervention, outcome. (X-over, wash out, other tx) cause and effect, stratification,
randomization, most difficult & expensive. Not good for rare dx, selection, allocation, observers.
Need for identical tx. "
Randomizaton correct answers sample = chance of selection for study, allocation=chance for
each group, nonrandom allocation =group assigned preferentially, biases results. removes
selection bias, best w/lg group. "
Simple Random Allocation correct answers coin toss, groups may be unequal in size at any
point, difficult to detect true difference. "
