Biostatistics

Question 1

What is the empirical rule of standard deviation in normal distributions? (aka how many samples values are found within 1, 2 and 3 SD)

Answer 1

68% of the sample values are found within ±1

SD, 95% are found within ±2 SD, and 99% are found within ±3 SD.

Question 2

How do you calculate the standard error of the mean? What does it represent?

Answer 2

SEM quantifies the uncertainty in the estimate of the mean and is calculated by dividing SD by the square root of the sample size.

Question 3

Using a CI, how could you interpret if two continuous variables are not statistically significant?

Answer 3

If the CI contains 0 (no difference between 2 variables)

Question 4

Using a CI, how could you interpret if odds ratio or relative risks are not statistically significant?

Answer 4

Value of 1 indicates no difference in risk and if CI includes 1, there is no statistical difference

Question 5

Describe the several types of student T tests

Answer 5

Parametric tests
One-sample test: Compares the mean of the study sample with the population mean
Group 1 vs Known population mean

b. Two-sample, independent samples, or unpaired test: Compares the means of two independent samples.
This is an independent samples test.
Group 1 vs Group 2
i. Equal variance test

c. Paired test: Compares the mean difference of paired or matched samples. This is a related samples
test.
Group 1
Measurement 1 Measurement 2

Question 6

Describe the different between analysis of variance vs t-test

Answer 6

ANOVA can apply to more than 2 groups

One-way ANOVA: Compares the means of three or more groups in a study; also known as singlefactor
ANOVA. This is an independent samples test.
Group 1 Group 2 Group 3

b. Two-way ANOVA: Additional factor (e.g., age) added
Young groups Group 1 Group 2 Group 3
Old groups Group 1 Group 2 Group 3

Question 7

Name other tests for independent samples that do not meet t-test or ANOVA requirements

Answer 7

Wilcoxon rank sum test, Mann-Whitney U test, or Wilcoxon Mann-Whitney test: Compare two
independent samples

Question 8

What does the Kruskal-Wallis test compare?

Answer 8

Compares three or more independent groups (related to one-way ANOVA)

Question 9

What tests can you run for paired samples?

Answer 9

Sign test and Wilcoxon signed rank test

Question 10

What does a Chi-square test measure?

Answer 10

Compares expected and observed proportions between two or more groups for nominal data

Question 11

What does a Fisher exact test measure?

Answer 11

Specialized version of the chi-square test for small groups (cells) containing less than
fve predicted observations for nominal data

Question 12

Which test compares paired samples for nominal data?

Answer 12

McNemar

Question 13

Define Type 1 Error

Answer 13

Conclude statistically significance when one does not actually exist (false positive)

Question 14

Define Type 2 Error

Answer 14

Concluding no difference exists when one truly does (false negative)

Question 15

Define Power

Answer 15

Probably of making a correct decision when Ho is false; the ability to detect differences between groups if one actually exists

Question 16

What is Pearson correlation?

Answer 16

strength of the relationship between two variables that are normally distributed; r = 1 means is more correlated

Question 17

What is Spearman Rank Correlation?

Answer 17

Nonparametric test that quantifes the strength of an association between two
variables but does not assume a normal distribution of continuous data.

Question 18

How would you interpret a coefficient of determination (r squared) of 0.8?

Answer 18

80% of the variability from the dependent variable can be explained by the independent variable

Question 19

Name which variables you can run chi square testing?

Answer 19

Nominal with 2 independent groups, nominal with more than >2 groups