Q: Which of the following is the correct formula for calculating the odds of an event occurring?

$$ \text{Odds} = \frac{p}{1-p} $$

Q: A study of 1272 children with ALL and 6238 without ALL found that 1020 with ALL and 5343 without ALL had significant social activity. What is the odds for children with ALL to be without exposure?

$$ \text{Odds} = \frac{252}{1020} = 0.247 $$

Question 1

Which of the following is the correct formula for calculating the odds of an event occurring?

Accepted Answer

$$ 	ext{Odds} = \frac{p}{1-p} $$

Question 2

A study finds that 19 out of 182 seniors and 2 out of 219 young patients died from WNV. What is the relative risk (RR) of mortality for seniors compared to young patients?

Accepted Answer

$$ RR = \frac{19/182}{2/219} = 11.4 $$

Question 3

Which of the following is NOT an assumption required for the chi-square test of independence?

Accepted Answer

Data must be paired.

Question 4

In a case-control study, which measure of association is most appropriate to use?

Accepted Answer

Odds ratio (OR)

Question 5

If the odds ratio (OR) for a disease between two groups is 1, what does this indicate?

Accepted Answer

There is no association between group and disease.

Question 6

A study of 1272 children with ALL and 6238 without ALL found that 1020 with ALL and 5343 without ALL had significant social activity. What is the odds for children with ALL to be without exposure?

Accepted Answer

$$ 	ext{Odds} = \frac{252}{1020} = 0.247 $$

Question 7

Which of the following best describes the main disadvantage of using the odds ratio (OR) instead of the risk ratio (RR)?

Accepted Answer

The interpretation of OR is not intuitive, especially when the event is common.

Question 8

Given a 2x2 table with all expected cell frequencies above 5, which test is most appropriate to assess association between two categorical variables?

Accepted Answer

Chi-square test of independence

Question 9

A paired t-test comparing the number of electric fish species upstream and downstream of tributaries yields $$t = 1.91$$, $$df = 11$$, $$p = 0.0826. $$What is the correct interpretation?

Accepted Answer

The difference was not statistically significant, but there is a considerable risk of type II error. Repeat the study with a larger sample.

Question 10

Which of the following formulas correctly calculates the odds ratio (OR) for a 2x2 table?

Accepted Answer

$$ OR = \frac{a/c}{b/d} = \frac{ad}{bc} $$

Question 11

If a study has low statistical power, which of the following is most likely to occur?

Accepted Answer

A true effect may not be detected (Type II error).

Question 12

Which of the following is a correct rule of thumb for expected cell frequencies in a chi-square test for a 3x3 table?

Accepted Answer

All cells should have expected counts of at least 1, and no more than 20% of cells should have expected counts less than 5.

Question 13

A power curve for a two-sample t-test shows that to detect a large effect ($$d = 0.8) $$with 80% power, the minimum sample size per group should be approximately:

Accepted Answer

$$ n = 25 $$

Question 14

Which of the following best describes the relationship between odds ratio (OR) and risk ratio (RR) when the event is rare?

Accepted Answer

OR closely approximates RR when the event is rare.

Question 15

In the context of effect size, which value of Cohen's $$d is $$considered a large effect?

Accepted Answer

$$ d = 0.8 $$

Question 16

A study finds an odds ratio (OR) of 11.8 for WNV mortality in seniors compared to young patients, with a 95% confidence interval of (3.3, 80.9). What does this result mean?

Accepted Answer

Seniors are significantly more likely to die from WNV than young patients.

Question 17

Which of the following best describes the power of a one-sided paired t-test with $$n = 30$$ and $$\alpha = 0.05 to $$detect a large effect?

Accepted Answer

About 97%

Question 18

If the p-value from a paired t-test is 0.0826, what is the p-value for the one-sided alternative that the mean difference is greater than zero?

Accepted Answer

0.0413

Question 19

Which of the following is a correct interpretation of a statistically significant but weak association (e.g., Cramer's V \u003c 0.1) between two categorical variables?

Accepted Answer

There is a significant but very weak association between the variables.

Question 20

In a 2x2 table, which test should be used if some expected cell frequencies are less than 5?

Accepted Answer

Fisher's exact test

Odds Ratios, Risk Assessment, and Power in Statistical Analysis

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