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Biostats
Mainolfi
66
Medical
Graduate
02/01/2012

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Term
Right Skew
Definition
tail to the right
mean toward the tail
positive skew
mean > median > mode
Term
Left Skew
Definition
tail to the left
mean toward the tail
negative skew
mean < median < mode
Term
Type I error
Definition
Rejection of a true null
False positive test
Term
Type II error
Definition
Acceptance of false null
False negative test
Term
Nominal Scales
Definition
Categorical data (race)
Chi Square
Discete numbers with no rank order
Term
Dicotomous scales
Definition
Yes or No
Chi Square
Term
Ordinal Scale
Definition
level of (pain, symptoms)
Discrete numbers with rank order only , no magnitude of diffrence between
Term
Interval Scale
Definition
Continuous and ordered: distance between variables has meaning
mean, sd, corelation, regression
Term
Ratio Scale
Definition
Needs a zero point
(blood cell counts)
Term
T-distribution
Definition
continuous probability distribution that arises when estimating the mean of a normally distributed population in
Measures the differences in the means
Situations where the sample size (less than 30) is small and population standard deviation is unknown

DF = N +1
sample size = 18
Term
Descriptive numbers for samples
Definition
parameter = population
statistic = sample
Term
Poisson Distribution
Definition
In general p should be less than 0.1 (small) an the number of trials should be >15 (large).

Need to be independent at a different time




Electrical system example: telephone calls arriving in a system.
Astronomy example: photons arriving at a telescope.
Biology example: the number of mutations on a given strand of DNA.
Term
Linear Regression analysis
Definition
y= bx + a
y = dependent
b= slope
a = intercept

linear regression is used to describe and association as inverse or
Term
Mutual Exclusive
Definition
Events that can not happen together
Probability of A or B happening
P(A) + P (B)
Term
Joint probability
Definition
events A or B occurring together or in succession

P(A) * P(B)
Term
Venn Diagram
Definition
circle in a diagram
Term
Standard deviation
Definition
Square root of variance
Term
Histogram
Definition
The class intervals are diffrent
each data point must fit into one class
open classes are not allowed
Term
Binomial Distribution
Definition
need fixed outcomes
can be approximated by the normal distribution.
Term
Coefficient of variation
Definition
100 times the population standards deviation divided by mean
Term
standard score (Z-scores) of normal distribution
Definition
the number of standard deviations from the mean
Term
Regression Equation estimate
Definition
explains the dependent variables. The higher the correlation the better the regression equation
Term
Kappa Stat
Definition
measures the extent that diffrent observations agree beyond what would be expected by chance alone.

K= Pobserved - Pexpected/ 100% - Pe
Term
NNT
Definition
1/ Attributable risk
Term
ROC
Definition
Reciver Opperator Test : determine the accuracy of the test.

Y axis = sen
X axis = 1-spec (FPR)

Area under curve proportional to accuracy of the test
Term
Parametric modeling
Definition
Used in Normal Distributions : more powerfull
Data must be interval or ratio
Can be used to describe measures of central tendancy
Term
Non-parametric Methods
Definition
non-normally distributed data
or Ordinal scale data
Term
Mean
Definition
Average
used for interval and ratio data
Term
Median
Definition
50% percentile
not affected by outliers
Usefull for Ordinal data
Term
Mode
Definition
most usefull when two clusters exist.
It is the highest point of the peak.
Usfull for nominal data
Term
Measures of varriability
Definition
range, standard deviation
Term
Range
Definition
can be influenced by outliers
Applicable to all data sets nomianal, ordinal, interval, ratio
Term
Interquartile range
Definition
range betweeen the 25th and 75th interval.
Directly related to the median
Applicable to ordinal, interval, and range
Term
Standard Deviation
Definition
Degree of scatter of individual data points about the sample mean

Usefull for normal distribution

= square root of varriance = sigma
Term
Varriance
Definition
= x-xi squared / n-1
= sigma saured

Applicable to interval and ratio data
Term
Standard Error of the mean
Definition
scatter about the mean = SD/ square root of n.

SEM always < SD
As n increases SEM decreases
Term
alpha
Definition
probablity of making a type 1 error
Term
B
Definition
probability of making a type II error
should be less than .2
Term
Power
Definition
1-B = probability of not making a type II error. = sensetivity

increase alpha = increase power
increase n = increase power
Term
Operating Charateristic Curve
Definition
function that relates the dependent variable B that results from independent values of alpha, and n
Term
One - tailed Test
Definition
More powerfull than a two tailed test.
Result must fall in either the top or bottom 5% of a distribution
Term
parametric stat tests
Definition
t- test (diffence between means)
ANOVA
Multiple Comparison models
Term
T-test
Definition
- Continuous data
- Normal distribution
- Variance same
- not paired (independent)

Paired T-test for dependent
Term
Risk Ratio
Definition
a / (a+b) / c (c+d)

OR shifts RR away from the Null.
Term
PPV
Definition
increase prevalence increase PPV

TP / (TP+FP) = a/ a+b
Term
ROC curve
Definition
Receiver operator Characteristics

Y = sensitivity
X = FPR

The greater the area under the curve the greater the accuracy.
Term
FNR
Definition
FNR = 1- sen = 1-TP
1-FNR = TP / sen
Term
FPR
Definition
FPR = 1-spec = TN
1-FPR = TN/ Spec
Term
Chi Squared
Definition
used if the variables are both categorical/ dichotomous.
DF= r-1

Chi squared pearsons = diffrences in proportions.
Term
ANOVA
Definition
- Continuous data
- 3 or more groups
- Independent
Term
Kruskal Wallis
Definition
- Continuous data
- 3 groups or more
- Skewed
- Dependent
Term
Friedmans test
Definition
- Continuous data
- 3 groups or more
- Skewed
- Independent
Term
Wilcoxen Rank sum
Definition
- Continuous data
- 2 groups
- Independent
Term
Wilcoxen Sign
Definition
-Continuous data
-2 groups
-Dependent / paired
Term
Tukey's Test
Definition
test of multiple comparison for adjusted data
Term
Chi Macnamare test
Definition
Univariate test to asses the diffrences in proportions.
Term
Linear Regression
Definition
Multivariate technique used for continuous data
Term
Logistic regression
Definition
Multivariate technique used for dichotomous or categorical data
Term
Chi mental test
Definition
test for linear trend w p values
Term
Cox proportional hazard curve
Definition
adjusted for confounders in the survival analysis curve.
Term
Survival Curve
Definition
Comparison of Kaplan Meir Curves for treatments.
Term
Hills Criteria
Definition
1.) Temporal
2.) Strenght of Ass
3.) Dose
4.) Consistency
5.) Plausibility
6.) Alt explanation
7.) Coherance
Term
Central Limit theorem
Definition
even if a population has a normal distribution the sample mean from repeated samples from this distribution approaches the normal distribution the larger the N . Sample size must be greater than 30
Term
Pearsons Correlation
Definition
R value give a indication of how closesly correlated
Term
Analysis of Varriants
Definition
AnoVA
Term
McNemars
Definition
Chi Squared for dependent
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