CLINICAL STATISITC 5

Question 1

What is Pearson’s correlation used for?

Answer 1

Pearson’s correlation measures the strength and direction of a linear relationship between two continuous variables.

Question 2

How is Spearman’s rank correlation different from Pearson’s?

Answer 2

Spearman’s rank uses ranks instead of actual values, making it a non-parametric measure less influenced by outliers.

Question 3

What are the properties of the correlation coefficient (r)?

Answer 3

Range: -1 to 1
r = 1: perfect positive linear relationship
r = -1: perfect negative linear relationship
r = 0: no linear relationship
Unitless

Question 4

What does a positive r value indicate?

Answer 4

As one variable increases, the other also increases.

Question 5

What’s the purpose of linear regression?

Answer 5

To predict the dependent variable (Y) using the independent variable (X).

Question 6

What does a negative r value indicate?

Answer 6

As one variable increases, the other decreases.

Question 7

How does regression differ from correlation?

Answer 7

Correlation treats both variables equally. Regression assumes one variable (X) predicts the other (Y).

Question 8

What is the general formula for a linear regression line?

Answer 8

y = b + mx, where:

y = dependent variable
b = intercept
m = slope
x = independent variable

Question 9

What does a slope of 0.7 in a regression model mean?

Answer 9

For every 1 unit increase in X, Y increases by 0.7 on average.

Question 10

in the example y = 1.5 + 0.7x, what is the predicted DMFT score when sugar consumption is 3 units?

Answer 10

y = 1.5 + 0.7(3) = 3.6

Question 11

Match the r value with interpretation:

r = -1 →
r = -0.6 →
r = 0 →
r = 0.3 →
r = 1 →

Answer 11

Match the r value with interpretation:

r = -1 → Perfect negative linear relationship
r = -0.6 → Moderate negative correlation
r = 0 → No correlation
r = 0.3 → Weak positive correlation
r = 1 → Perfect positive linear relationship

Question 12

What is relative risk (RR)?

Answer 12

The ratio of the probability of an event in the exposed group vs the non-exposed group.

Question 13

In the example, what is the absolute risk difference between vitamin and placebo groups for periodontal disease?

Answer 13

36.4% (vitamin) - 62.9% (placebo) = -26.5%

Question 14

What is the relative risk for the same example?

Answer 14

36.4 / 62.9 = 0.58

Question 15

How do you interpret RR = 0.58?

Answer 15

42% relative risk reduction in periodontal disease in the vitamin group.

Question 16

What is an odds ratio (OR)?

Answer 16

The ratio of odds of exposure in the diseased group to the odds in the non-diseased group.

Question 17

How do you calculate odds from probability?

Answer 17

Odds = p / (1 - p)

Question 18

How do you interpret an odds ratio of 0.34?

Answer 18

There’s a 66% reduction in the odds of periodontal disease in the vitamin group.

Question 19

How do odds ratios compare to risk ratios?

Answer 19

OR is larger than RR when RR > 1
OR is smaller than RR when RR < 1

Question 20

What is survival analysis used for?

Answer 20

To analyze time-to-event data like death, disease onset, recovery, etc.

Question 21

What does the Kaplan-Meier curve represent?

Answer 21

It shows the survival probability over time and allows comparison between groups.
BAR- Shows drop out - doesn’t change survival tho

Question 22

What is censoring in survival analysis?

Answer 22

When participants don’t experience the event during the study (lost to follow-up, drop out, or study ends).

Question 23

What is the dependent variable in regression?

Answer 23

The outcome variable being predicted (Y).

Question 24

What is the independent variable in regression?

Answer 24

The predictor variable (X).

Question 25

When do you use risk ratios vs odds ratios?

Answer 25

Use risk ratios for cohort studies (prospective) Use odds ratios for case-control studies

Question 26

What is function of multivariable analysis

Answer 26

- control for confounders - test for interactions between predictors - Improve

Question 27

What is the prevalence rate

Answer 27

= the proportion of a population that are cases at a point in time.

Question 28

What is the relative risk

Answer 28

rate of condition among exposed divided by rate of condition among unexposed

Question 29

what does relative risk = 1 mean

Answer 29

means no difference

Question 30

Relative risk > 1

Answer 30

shows existence of an association between exposure and disease

Question 31

What is the Odds ratio

Answer 31

The odds of an event is the ratio of the probability of occurrence of an event to the probability of non-occurrence

Question 32

Why not compare mean time-to-event between your groups using a t-test?

Answer 32

ignores censoring

Question 33

. Why not compare proportion of events in your groups using risk/odds ratios?

Answer 33

ignores time THATS WHY WE NEED TO USE SURVIVAL ANALYSIS

Question 34

What are limitations of Kaplan Meier

Answer 34

Mainly descriptive Doesn’t control for covariates Requires categorical predictors Can’t accommodate predictor variables that change over time

Question 35

Which of the following data sets is likely to lend itself to survival analysis? A case-control study of caffeine intake and breast cancer. A randomized controlled trial where the outcome was whether or not women developed breast cancer in the study period. A cohort study where the outcome was the time it took women to develop breast cancer. A cross-sectional study which identified both whether or not women have ever had breast cancer and their date of diagnosis.

Answer 35

Question 36

Investigators compared mean cholesterol level between cases with heart disease and controls without heart disease. Which of the following is likely the most appropriate statistical test for this comparison?

Answer 36