Biostatistics Flashcards
Health promotion prevention category
Primary prevention
Enables people to improve their health
Health risk assessment method
Questionnaires collecting demographic, medical, lifestyle, family history information to calculate a patient’s risk age.
Percent of data between +/- 1 SD
68%
Percent of data between +/-2 SD
95%
Percent of data between +/- 3 SD
99.7%
The parameter of diagnostic tests most important for screening
High sensitivity
Decreasing the cutoff point will result in:
Sensitivity: increased True positive: increased False positive: larger increase PPV: decreased False negative: decreased
Hawthorne effect (observer effect)
The tendency of study subjects to change their behavior as a result of their awareness that they are being studied
Affects validity
Berkson’s bias
Selection bias created by choosing hospitalized pts as the control group
Pygmalion effect
A researcher’s beliefs in the efficacy of treatment can potentially affect the outcome
Chi-square test for independence
To test the association between two categorical variables
Two-sample z test
Two/sample t test
Used to compare 2 group means(numerical values), not categorical variables.
ANOVA
Used to compare the means of 2 or more groups
Test parameter influenced by disease prevalence
PPV
NPV
Test parameter influenced by pretest probability
NPV
Validity of a test
The test measures what it is supposed to measure
Positive likelihood ratio
the probability of a person who has the disease testing positive divided by the probability of a person who does not have the disease testing positive.
=sens/ (1-spec)
Negative likelihood ratio
the probability of a person who has the disease testing negative divided by the probability of a person who does not have the disease testing negative
=(1-sens)/ spec
In a smoker, diabetic, alcoholic, sedentary, hypertensive individual, what is the intervention most likely to reduce overall mortality rate?
Smoking cessation
Negative skewed distribution curve
Peak (mode) to the right
Mean to the left
Median in between
Positively skewed curve
Mode to the left
Mean to the right
Median in between
NNT calculation
1/ARR
ARR
Control rate - treatment rate
RRR
ARR/Control rate
Relative risk
Treatment rate/control rate
Or
Risk of outcome in exposed / risk of outcome in non-exposed
Type II error (beta) definition
The probability of concluding there is no difference when such a difference truly exists
Power of study
1- beta
The ability of a study to detect a difference when such a difference truly exists
Type one error (Alpha)
The probability of seeing a difference when there is no difference in reality
Definition of a reliable test (precision)
It gives similar or very close results on repeat measurements
Validity or accuracy
A test’s ability to measure what it is supposed to measure
How to quantify the reliability of a test
In terms of the coefficient of variation ( standard deviation divided by mean of repeated measurements) generally expressed as a percentage
The odds ratio measurement
Is a measure of association between an exposure and an outcome
All in favor of association/all against an association
=ad/bc
The significance of confidence of interval in a meta-analysis study
If the range of confidence of interval does not include a null value, the result is statistically significant.
If the CI crosses the null value then there is no statistically significant difference between the groups.
Matching Method
Used in design stage of case-control studies to control confounding
Stratified analysis
Can be used to negate confounding effect
Confounding effect vs effect modification in stratified analysis
Stratified analysis disappears the observed difference in the study due to “confounding effect” but potentiates the observed difference due to “effect modification”
Case fatality rate measurement
Calculated by dividing the number of fatal cases by the total number of people with the disease
Atributable risk percentage
100 x (Risk in exposed- Risk in unexposed) / risk in exposed
Attrition bias
In prospective studies if loss to follow-up occurs disproportionately between the exposed and unexposed groups attrition bias can result if the lost subjects differ in the risk of developing the outcome compared to the remaining subjects.
It is a form of selection bias.
Latency definition
The concepts of latency. It can be used for infectious diseases, risk factors and risk reducers.
The time between exposure and clinically apparent disease.
The rare disease assumption
Refers to the fact that the odds ratio approximates RR When disease prevalence is low
The relative risk null value
1
For a result to be considered statistically significant, its corresponding CI must not contain the null value
The relationship between CI and P-value
A statistically significant 95% CI corresponds to a P-value <0.05. A statistically significant 99% CI corresponds to a P-value <0.01.
Mean +/- 1.96 SD would cover
95% of the observations
The mean +/- 2.58 SD would cover
99% of the observations
SE= standard error
SD/√n
A way to account for variability due to sampling
95% CI= mean +/- 1.96 SE
99% CI= mean +/- 2.58 SE
Relative risk, relative rate are for which type of study?
Cohort
Because these are incidence measures, they cannot be calculated from case-control studies
Exposure odds ratio is for which type of study?
Case-control
Prevalence odds ratio is for which type of study?
Cross-sectional
Generalizability or external validity
The applicability of the obtained results beyond the cohort that Was studied
