Stats

Question 1

Small group, categorical data - best test

Answer 1

Fischer exact

Question 2

Large groups, categorical data - best test

Answer 2

Chi square

Question 3

Continuous data, different individuals - best test

Answer 3

Unpaired T test

Question 4

Continuous data, matched samples - best test

Answer 4

Paired T test

Question 5

Continuous or ordinal data for non-normally distributed data - best test
“Nonparametric test to compare differences between two groups when dependent variables are ordinal or continuous”

Answer 5

Mann Whitney U

Question 6

What is a Funnel Plot

Answer 6

Used to eval for bias in meta analysis/systematic reviews

Question 7

Define sensitivity / specificity

Answer 7

Sens = TP / TP+FN = a/a+c
Spec = TN / TN+FP = d/d+b

 disease t       +      - e +  TP   FP s  -  FN   TN t

SENS/SPEC VERTICAL

Question 8

What studies determine prevalence vs incidence

Answer 8

Prev = cross sectional survey
Incidence = new dx in a period of time = prospective cohort

Question 9

95% CI is what mean/SD

Answer 9

Mean +/- 1.96 SD

90: 1.62
98: 2.33
99: 2.58

Question 10

Define PPV and NPV

Answer 10

disease
t + -
e + TP FP
s - FN TN
t

PPV = TP/TP+FP
NPV = TN/TN+FN

HORIZONTAL

Question 11

What is power
What is T2 error

Answer 11

Power = 1 - probability of T2 error (beta)
= 1- 20% = 80%
80% chance of doing study that finds p<0.05 if true association exists

T2 error = beta = study reports a negative result when a true difference exists
- False negative
- Ok 20% time

If decrease the power, increase the confidence if a negative result is found

Question 12

What statistic is used for intra observer reliability

Answer 12

Kappa

Question 13

Describe a cohort study
What statistic can be calculated

Answer 13

No comparison group
Know a potential risk factor - do your cohort develop the outcome if they have the risk factor
Often prospective…. INCIDENCE

Question 14

Describe a case control study

Answer 14

ID pts with infection (cases)
Then go find their risk factor
By matching to controls

Question 15

What are the 4 phases of research by FDA

Answer 15

1: pharmacology, det if drug is safe, dose finding
2: efficacy, does drug work?, compare to other interventions
3: confirm efficacy in larger trial
4: post marketing surveillance

Question 16

What are the 5 levels of evidence?
What about systematic review/meta analysis

Answer 16

1 RCT
2 Cohort (prospective), poorly done RCT
3 Case control
4 Case series
5 Expert opinion

SR/MA - lowest level you incorporate into the review determines level of evidence

Question 17

Define bias vs confounding
How do you combat each

Answer 17

Bias = you put in
- Errors in research methodology
Combat w/ better study design

Confounding = you didn’t know something was associated
- Unaccounted variables that explain associations
Combat w/ randomization

Question 18

Define these types of bias
Selection
Detection
Recall
Interviewer
Performance
Hawthorne Effect

Answer 18

Selection - if study says “per surgeon preference” then this is selection bias
- Randomize to reduce!

Detection - tend to look more carefully for an outcomes in one group

Recall - knowledge of disease alters recall
- Pt w/ OA will recall a distant injury vs pt wo sx

Interviewer - knowledge of the treatment alters assessment

Performance - systematic, unintended difference in care
- Generalists vs trauma surgeons doing X case

Hawthorne Effect - subject behavior changes bc know being watched
- Room turnover gets better when people know turnover times are being watched

Question 19

Equation for RR
How do you interpret results

Answer 19

RR = risk in exposed / risk in unexposed

RR = 1, risk equal exposed to non exposed
RR>1 = exposed > unexp
- Positive associated between exposure and outcome (?causal?)
1<RR = exposed < unexp
- Negative “ “ (?protective?)

Remember 95% CI for RR cannot cross 1 to be sig!

Question 20

What is type 1 error
What does alpha < 0.05 mean

Answer 20

Saying an association exists, when it does not
False positive
Your study finds a difference when a diff doesn’t actually exist

Alpha < 0.05 = 5% of time get a difference in the data when it isn’t real