BIOSTATISTICS Flashcards
What’s lead time bias?
Is the erroneous finding of prolongation of survival when just the illness was detected earlier .
What’s latent period factor in the effect of drugs or change in the risk?
Period needed to show differences
What is Observer bias ?
Is when the observer misclassifies data according its interpretation or its expectations
What’s selection bias ?
Inappropriate non-random selection
When use odds ratio?
CASE-CONTROL STUDIES !!!
RETROSPECTIVE!!!!
OR=ad/bc
“Patients with COPD had higher odds of a
history of smoking than those without COPD.”
When use Relative Risk?
COHORT STUDIES!!!!
PROSPECTIVE!!!!!
RR=[a/(a+b)] / [c/(c+d)]
“Smokers had a higher risk of developing COPD
than nonsmokers.”
What’s selection bias ?
Selection of unrepresentative sample ( all healthy ,all sick)
ATTRITION BIAS : a very different group of data is loss
What’s missclassification bias?
Use the wrong method to classify the groups
Big difference between case-control and cross-sectional study?
CASE -CONTROL : Make sick and non-sick subjects
CROSS-SECTIONAL: take random subjects
Big characteristic of randomized clinical trial?
COMPARES >2 TREATMENTS
What’s type II(beta) error?
Falsely conclude there is NO difference
FALSELY NOT REJECT
What’s type I (alpha) error?
Falsely conclude there is a difference
Falsely REJECT
The best answer to a college asking about a patient of your is …
No, I cannot say whether she is my patient .
How confounding bias can be controlled?
MATCHING
used in case control studies
Matching the subjects by age , race , gender etc…
What is statistical power?
1-beta
SAMPLE SIZE
Cause of mortality in TCAs overdoses?
Cardiac arrhythmia say inhibit fast Na channels
Refractory hypotension by alpha agonist
What is the center of study of ECOLOGICAL STUDY?
COMPARE POPULATIONS!!!!!!!
used to make HYPOTHESIS NOT CONCLUSIONS!!!!
What’s nested case-control?
Begins whit cohort studies
The patients with the outcome go to case - control studies
How the protest probability affects the NEGATIVE PREDICTIVE VALUE?
⬇️Pre-test probability ⬆️ NPV
⬆️Pre-test probability ⬇️ NPV
What is near miss?
Error recognized before any harm
What’s sentinels event?
Unexpected event involving death or serious physical or psychological injury that’s REQUIERS IMMEDIATE INVESTIGATION
Which calculation can be used to comparete different tests whit different normal values?
Coefficient variance
What’s a reliable test?
A test whit very similar results in the same patient is REPRODUCIBLE
What’s a valid test ?
Is the ability to measure what is suppose to measure
Very similar whit GOLD STANDARD
What’s the attributable risk percent in the exposed?
Percentage of disease attributable to the Exposition
=100x[(RR-1)/RR]
What’s referral bias ?
You cannot compared a big specialized hospital whit a small health center even if there is the same illness
What’s detection bias?
The risk factor increase the probability of diagnosis because they perform a lot of tests
What’s sampling bias?
Very sick people cannot be compared whit sick people not as Ill
How calculate the probability of a group of outcomes?
MULTIPLY THE INDEPENDENT EVENTS
What is the confidence interval formula?
Mean➕➖Z(S/√N)
Z 95%=2. 99%=2.5
S standard deviation
N population
What’s late-Look bias?
Miss severe cases because the patients dye before the study
What happen Whit confidence intervals which contain de number 1?
IS NOT STATISTICALLY SIGNIFICAT!!!!!
Alpha error is possible ONLY if the p value is….
p<0.05!!!!!
When do you use ANOVA, Chi-square test, Meta-analysis , multiplier linear regression, Pearson correlation coefficient, t-test?
ANOVA compare means between 2 or more independent groups
Chi-square test association between 2 categorical variables
Meta-analysis compare a lot of good studies
multiplier linear regression linear relation btw 1 dependent & 2 inde
Pearson correlation coefficient Strength & dirección of linear relation between 2 variables
t-test. Two groups compared
What is the equation for number need to treat?
Is equal to number needed to harm NNH…
NNT=1/ARR
Absolute risk reduction = ARR= control %-treatment %
What is the Hawthorne and Pygmalion effect?
Hawthorne : observer effect
Pygmalion: all of mine is better
Explain which measure two-sample t test, Two-sample z test, Chi-square, Analysis of variance.
two-sample t test 2 groups means
Two-sample z test 2 groups means
Chi-square. 2 categorical variables
Analysis of variance. Means of >2 groups
How VPP and VPN are affected by prevalence?
⬆️prevalence ⬆️VPP
⬆️prevalence ⬇️VPN
What’s effect modification?
When the outcome is modified by another variable
Ex. Thrombosis in women who take estrogens Vs Thrombosis In SMOKER women who take estrogens
Types of distribution?(3)
NORMAL DISTRIBUTION 🔼 mean=median=mode
POSITIVE SKEWED 📉 mean>median>mode
NEGATIVE SKEWED📈 mean<median<mode
