BIOSTATS Flashcards
What does Bayesian statistics allow you to do?
Calculate conditional probabilities
What does the Chi squared test allow you to do? What type of answers does it use?
Compare results from 2 independent populations…use binary answers
If you have a highly sensitive test…what result are you certain is correct?
A negative. Like airport security…want to have highly sensitive test. You know that the people who get thru are fine. You may catch a few innocent people in the process, however.
If you have a highly specific test…what result are you certain is correct?
A positive. this would be bad for airport security. The only thing you know is that if you get a positive & catch somebody they ARE guilty. But plenty of guilty people may have sneaked thru.
What is the difference b/w disease prevalence & incidence?
prevalence–how widespread the disease is
incidence–rate of occurrence of new cases of the disease
What is selection bias?
the reality that a certain type of people are willing to participate in studies…may not be totally representative of the population
What are 2 ways to randomize?
Blocked randomization
Stratification
As a sample size increases, _____ increases but you also establish a more firm ________.
range increases when sample size increases.
You also get a steady state w/ more normal values.
What is internal validity?
How confident you are that your dependent variables in your study solely changed b/c of your independent variable.
Basically….that you had a sound study design.
What is external validity?
Extent to which the results can be generalized to other people or settings.
What are some things that can endanger internal validity?
Maturation Testing Instrumentation Statistical Regression Selection Bias Experimental Mortality
What are some things that can endanger external validity?
Pretesting
Interaction
Multiple Treatments
Setting
What is the relationship b/w standard deviation & variance?
Standard deviation is the square root of variance.
What determines your degrees of freedom?
n-1
A peak on a graph would represent what measurement of the data?
the mode!!
If your mean is greater than your median & you have a long right tail…what is your skew?
Right/positive skew
If your median is greater than your mean & you have a long left tail…what is your skew?
Left/negative skew
T/F the chi square test has a larger p value than the z test.
False. They have the same p value.
What question is asked with:
the predictive value of a positive result
What is the probability that the patient actually has this disease? They tested positive.
True Positive/True Positive + false positive
What question is asked with:
the predictive value of a negative result
They tested negative. What is the probability that the patient really doesn’t have the disease?
True negatives/True negatives + False negatives
Single subject experiments have high _____ validity, but low _____ validity.
High internal validity
low external validity
What is a confidence interval?
CL = 1 - alpha
how confident you are that the interval contains the true average value
What is the role of the null hypothesis?
it says that there is no relationship b/w 2 things…it is your job in your experiment to reject the null hypothesis.
What is the p value?
ranges from 0-1
Tells us something about our null hypothesis.
If p value is low; reject the null. Yay!
If p value is high; accept or fail to reject the null. : (
What is the t statistic?
Used when sample is small & it follows a normal distribution
What is the z score?
compares a sample to a population…used when sample is large
What is the alpha level?
Called the significance level
The probability of rejecting the null hypothesis when it is true.
Usu alpha= 0.05. It ranges from 0-1
If you are making airplanes: make that alpha low; if you are making paper airplanes: make that alpha high
When is something statistically significant?
When the result of the hypothesis test is a p value less than 0.05
T/F P value is the probability that your null hypothesis is true.
FALSE
If the p value is greater than alpha…what does that mean for the null hypothesis?
We fail to reject the null hypothesis. : (
What is type I error? What represents this error?
Rejecting the null hypothesis when it is true.
alpha represents this.
What is type I error? What represents this error?
Rejecting the null hypothesis when it is true.
alpha represents this.
What is type II error?
failing to reject the null when it was false.
What is type II error?
failing to reject the null when it was false.
If you want a really awesome test…you choose a small/large alpha & make Type I/II errors more common.
small alpha
make it hard to reject the null
make Type II errors more common
If you want a really awesome test…you choose a small/large alpha & make Type I/II errors more common.
small alpha
make it hard to reject the null
make Type II errors more common
