Stats Gross

Question 1

What is a case-control study

Answer 1

Observational, retrospective

A study done using a population of subjects that are selected based on the outcome of interest (cases) and compares them to a similar population of patients who don’t have the outcome of interest (controls). Investigators look back to identify characteristics (exposures) that are linked to the outcome

Question 2

What is a cohort study

Answer 2

Observational, prospective OR retrospective

A study that defines two groups of patients (cohorts) - one which has been exposed (e.g., received active treatment) and one which has not been exposed (control) - and observes to see if an outcome of interest happens in either group.

Question 3

Intent-To-treat vs Per-Protocol Analysis

Answer 3

Intent-to-Treat (ITT) – analyzing subjects according to the group to which they were randomized

Per-Protocol (PP) – analyzing only those subjects who adhered to the treatment according to the protocol

Question 4

What is Type 1 Error

Answer 4

A Type 1 error occurs if we reject H0 when, in fact, H0 is true; If this happens, we will have a false positive

AKA say there is a difference when there really isn’t a difference

Question 5

What is Type 2 Error

Answer 5

o A Type 2 error occurs when we accept H0 when, in fact, H0 is false; If this happens, we will have a false negative

AKA say there is no difference when there really is a difference

Question 6

Probability of Type 1 Error

Answer 6

Alpha, normally 0.05

1 time out of 20 we will falsely reject H0

Question 7

Probability of Type 2 Error

Answer 7

Beta, normally 0.20

Question 8

Prevalence vs Incidence

Answer 8

Prevalence: Total number of cases (EXISTING disease) divided by total population; Tells how much disease there is right now (burden of disease)

Incidence: Measures frequency of disease in a population; How many people per year acquire the disease?

Question 9

Odds Ratio calculation

Answer 9

Odds of outcome given EXPOSURE versus non-exposure to a substance or event (ratio of odds)

OR = Odds case was exposed/Odds control was exposed
OR=A/C / B/D
OR=AD/BC

Question 10

Relative Risk Calculation

Answer 10

Ratio of incidence of outcome among exposed group/incidence of outcome among non-exposed

RR=Risk among exposed/Risk among non-exposed
RR=(A/A+B)/(C/C+D)

Question 11

Relative Risk Reduction

Answer 11

Tells how much treatment reduced the risk of the outcome relative to controls who did not get treatment

RRR=1-RR

Question 12

Absolute Risk Reduction

Answer 12

Absolute risk difference in event rate

ARR=(A/A+B) - (C/C+D)

Question 13

How to calculate NNT?

Answer 13

1/ARR

Question 14

Which test if data is:
Nonparametic
Nominal
Two groups, independent

Answer 14

Chi-square or Fisher exact test (if <5 in any cell or n<20)

Question 15

Which test if data is:
Nonparametic
Nominal
3+ groups, independent

Answer 15

Chi-square or Fisher exact test (if <5 in any cell or n<20)

Question 16

Which test if data is:
Nonparametic
Ordinal
2 groups, independent

Answer 16

• Mann-Whitney U
• Wilcoxon rank sum test
• Wilcoxon-Mann-Whitney test

Question 17

Which test if data is:
Nonparametic
Continuous, not normally distributed
2 groups, independent

Answer 17

• Mann-Whitney U
• Wilcoxon rank sum test
• Wilcoxon-Mann-Whitney test

Question 18

Which test if data is:
Nonparametic
Ordinal
3+ groups, independent

Answer 18

Kruskal-Wallis

Question 19

Which test if data is:
Nonparametic
Continuous, not normally distributed
3+ groups, independent

Answer 19

Kruskal-Wallis

Question 20

Nonparametric
Nominal
2 groups: Before & After a Single Treatment

Answer 20

McNemar test

Question 21

Nonparametric
Nominal
3+ groups: Before & After a Single Treatment

Answer 21

Cochran Q test: Mantel-Haenszel test

Question 22

Nonparametric
Ordinal
2 groups: Before & After a Single Treatment

Answer 22

Wilcoxon signed-rank test

Question 23

Nonparametric
Ordinal
3+ groups: Before & After a Single Treatment

Answer 23

Friedman ANOVA by ranks

Question 24

Nonparametric
Continuous, not normally distributed
2 groups: Before & After a Single Treatment

Answer 24

Wilcoxon signed-rank test

Question 25

Nonparametric
Continuous, not normally distributed
3+ groups: Before & After a Single Treatment

Answer 25

Friedman ANOVA by ranks

Question 26

Parametric
Continuous, normally distributed
2 groups

Answer 26

Student t-test

Question 27

Parametric
Continuous, normally distributed
3+ groups

Answer 27

ANOVA followed by post hoc testing

Question 28

Parametric
Continuous, normally distributed
2 groups: Before & After a Single Treatment

Answer 28

Paired t-test

Question 29

Parametric
Continuous, normally distributed
3+ groups: Before & After a Single Treatment

Answer 29

Repeated measures ANOVA

Question 30

What is study bias? Give examples

Answer 30

Systematic, nonrandom variation in study metholodgy and.or data collection process that results in an incorrect estimate of association between exposure and outcome

Selection bias
Information bias
Recall bias
Interviewer bias
Misclassification bias
PUblicaiton bias
Confounding variables

Question 31

Categorical data: what is Nominal? Ordinal?

Answer 31

Nominal = categories w/o rank (i.e., sex, race, presence/absense of disease)

Ordinal = categories with rank (i.e., likert scale, pain score)

Question 32

Continuous data: what is Ratio? Interval?

Answer 32

Ratio = HAS absolute zero where zero=none (HR, BP)
- Can calculate ratio of 2 measurements with ratio

Interval = NO absolute zero (temp)