**Question:** In a 3 x 3 table, degree of freedom is:

A. Number of rows - Number of columns
B. Number of rows - 1
C. Number of rows - 2
D. Number of rows - 1

**Core Concept:** In statistics, the degree of freedom (DF) is a measure of the number of values in an analysis that can vary. In a 3 x 3 table, the degrees of freedom can be calculated using the formula specific to the given arrangement.

**Why the Correct Answer is Right:** In a 3 x 3 table, the correct formula for calculating degrees of freedom (DF) is:

Correct Answer: D. Number of rows - 1

This is because the number of rows represents the number of independent observations, and we subtract 1 to account for the fact that the mean is a fixed value (the sum of all values divided by the degrees of freedom).

**Why Each Wrong Option is Incorrect:**

A. This option is wrong because it counts the number of rows, not the independent observations:
- Number of rows - Number of columns = 3 - 3 = 0

B. This option is incorrect because it subtracts one more than necessary:
- Number of rows - 1 = 3 - 1 = 2

C. This option is wrong because it subtracts two, which is more than needed:
- Number of rows - 2 = 3 - 2 = 1

**Clinical Pearl:** Degrees of freedom calculations are essential for understanding statistics in medical research and analysis. It helps in interpreting the results and drawing meaningful conclusions.