Sensitivity
TP / (TP + FN)
Specificity
TN / (TN + TP)
Positive Predictive Value
TP / (TP + FP)
Negative Predictive Value
TN / (FN
... [Show More] + TN)
Incidence Rate
# of new cases in a certain time period / population that is at risk during that time period
This looks at new incidences occurring during a time period
Prevalence
# of existing cases / population at risk
Looks at ALL current cases
Odds Ratio
(a/c) / (b/d) OR ad / bc
Relative Risk
[a / (a + b)] / [c / (c + d)]
Attributable Risk
(a / (a+b) ) - (c / (c+d) )
Gaussian curve standard deviation %'s
+/- 1 SD = 68%
+/- 2 SD = 95%
+/- 3 SD = 99.7%
Type 1 error (alpha)
you sAw a difference that did not really exist
(convicting an innocent man)
Type 2 error (beta)
you were Blind to a difference that did exist
(setting a guilty man free)
Power
1-beta or in other words, 1 - type 2 error
(increasing sample size will increase power, there is POWER in numbers. Also, increasing Precision will increase power)
SEM
SD / square root of n
Confidence Interval
range from [mean - Z (SEM)] to [mean + Z (SEM)]
Z = 1.96 for 95% CI
Z = 2.58 for 99% CI
On the test, it may be easier to remember the Z values as 2 and 2.5 for easier calculations and memorization
t - test
checks difference between the means of 2 groups
ANOVA
checks difference between the means of 3 or more groups
Chi square
tests the difference between 2 or more percentages or proportions of categorical outcomes (NOT THE MEAN VALUES)
Number needed to treat
1 / absolute risk reduction
Number needed to harm
1 / attributable risk
Selection Bias
non-random assignment to participation in the study group
Recall Bias
Knowledge of presence of disorder alters recall by subjects
Sampling Bias
Subjects are not representative of the general population; therefore, results are can be generalized
Late-Look Bias
Information gathered at an inappropriate time (like surveying dead people)
Procedure Bias
Subjects in different groups are not treated the same
Confounding Bias
Occurs when factor is related to both exposure and outcome, but is not the the causal pathway; factor distorts or confuses effect of the exposure on outcome
Lead-time Bias
Early detection confused with increased survival; seen with improved screening (the natural history of the disease is not changed but catching things earlier, like cervical cancer, makes it seem as though survival increased)
Observer-expectancy effect
Occurs when a researcher's belief in the efficacy of a treatment changes the outcome of that treatment
Hawthorne effect
Occurs when the group being studied changes its behavior because they know they are being studied
Case control study
compares a group of people with a disease to a group of people without a disease
Asks, what happened?
Measures odds ratio
Cohort study
Compares a group wit ha given exposure or risk factor to a group without the exposure
Asks who developed disease?
Measures relative risk
Cross-sectional study
Collects data from a group of people to asses frequency of disease
Asks what is happening?
Measures disease prevalence
Twin concordance study
compares the frequency with which monozygotic twins or both dizygotic twins develop the same disease [Show Less]