Biostatistics Flashcards
attack rate =
number of individuals who become ill divided by the number of individuals who are at risk of contracting that illness
the ______ of test refers to its ability to correctly ID those with the disease. A highly ______ test should be chosen over a highly ______ test when screening for life threatening diseases
sensitivity
sensitive
specific
1 SD away from the mean =
2 SD away from the mean =
3 SD away from the mean =
68% (16 on each side of the curve)
95% (2.5 on each side of the curve)
99.7% (.15 on each side of the curve)
If the CI crosses the null value = 0, then there is
no statistical significance
in a _________ subjects are randomly allocated to a sequence of 2 or more treatments given consecutively. A washout period is often added between treatment intervals to limit the confounding effects of prior treatment
Cross over study
_______ is present when the effect of the main exposure on the outcome is modified by the presence of another variable
effect modification
the _________ of a test refers to its ability to correctly ID individuals without the disease
specificity
the mean is the ______
the mode is the ______
the range is the _____
an outlier will not effect the ____
average
most frequent
difference from largest to smallest
mode
PPV =
TP/(TP+FP)
incidence corresponds to the ________ of a disease in a certain population at risk over a given period of time. _______ is the total number of cases in the population over a given period of time
number of new cases
prevalence
True negatives =
false positives =
specificity =
sensitivity =
specificity x number of patients confirmed without the disease
1 - specificity x the number of patients confirmed without he disease
d/(b+d)
a/(a+c)
the cutoff value of a quantitative diagnostic test determines whether a given result is interpreted as positive or negative. Lowering the cutoff point typically causes ________, which decreases the false negative number and increases the sensitivity and decreases the specificity. =
more patients with the disease to test positive
cases and controls should be selected based on _________, not exposure status
disease status
prompt treatment of grpA strep pharyngitis could reduce the incidence of
ARF
matching is used in case controls studies in order to control ___________
confounding variables
the mean measure of association in a case control study used to compare exposure status of people with disease vs people without disease is the ______
odds ratio
the _______ or observer effect is the tendency of study subjects to change their behavior as a result of their awareness that they’re being studied
Hawthorne effect
ARR =
event rate in the control group - event rate in the treatment group
statistical ______ = (1-Beta) is the probability of rejecting the null hypothesis when it is truly false. It is typically set at 80% and depends on sample size and difference between outcomes
power
allele frequency =
phenotypic frequency
mutant allele frequency from disease prevalence
p + q = q
p^2 + 2pq + q^2 = 1
square root(q^2) = q
The odds ratio is =
ad/bc
exposure to a risk factor or risk reducing factor sometimes occurs years before clinical manifestations of a disease are evident. THis is called
latent period
if the 95% CI does not cross the null value, the p value must be
<0.05
if events are independent (blood samples) the probability that all events will turn out the same is the ________ of the separate probabilities for each event
product
in a _________ exposure and outcome are measured simultaneously at a particular point in time (snapshot)
cross sectional
________ values are influenced by disease prevalence in a target population while sensitivity, specificity, and likelihood ratios are not prevalence dependent
positive and negative predictive values
CI of mean =
Mean + or - 1.96(SDsquareroot(n))
Number needed to harm =
ARR =
1/ARR
adverse event rate in experimental group - adverse event rate in control group
relative risk reduction = (absolute risk - absolute risk treatment)/ARcontrol
or Standard recurrence rate - [desired recurrence rate reduction x (_________)]
standard recurrence rate
______ occurs when new test diagnoses a condition earlier than conventional studies, causing an apparent increase in survival time
lead time bias
a _____ is used to compare the difference between the means of 2 groups. ____ compares the difference between the means of 2 or more groups.
T test
ANOVA
____ is the probability of developing a disease over a certain period of time. To calculate this probability, divide the number of affected subjects by the total number of subjects in the corresponding exposure group
Risk
the _______ represent the risk of an outcome in the exposed divided by the risk of that outcome in the unexposed. this is equal to [a/(a+b)]/[c/(c+d)]
Relative risk
the unit of analysis in ______ is populations not individuals
ecological studies
______ results from study participants inaccurate recall of past exposure and occurs most often in retrospective studies
recall bias
a studies power increases as its _______. therefore the larger the sample, the greater the ability of a study to detect a difference when one truly exists
sample size increases
the attributable risk percent in the exposed represents the excess risk in the exposed population that can be attributed to the risk factor (smoking). It can be derived by ARPexposed =
100x [(RR-1)/RR]
________ is calculated by dividing the number of fatal cases of a disease by the total number of people with that disease or condition
case fatality rate
in prospective studies, disproportionate loss to follow up between the exposed and unexposed groups creates the potential for attrition bias, which is a form of
selection bias
a factor that prolongs disease duration (improved quality of care) will ________________
increase disease prevalence
