**Question:** Significance of difference between two proportions is best studied by:

A. Z-test
B. Chi-square test
C. Odds ratio
D. Fisher's exact test

**Core Concept:** When comparing two proportions, determining if the observed differences are statistically significant is essential to draw meaningful conclusions from the data. The appropriate statistical test depends on the nature of the data and the research question.

**Why the Correct Answer is Right:**
The Z-test is the correct answer because it is used for comparing proportions when the sample sizes are large (n>=30) and the data is normally distributed. In this case, the Z-test provides a standardized measure of the difference between proportions, making it easier to interpret and compare the results.

**Why Each Wrong Option is Incorrect:**

A. Chi-square test is used for comparing proportions when the sample sizes are small (n<30) or when the data is categorical (e.g., nominal or ordinal). It is not suitable for large sample sizes and continuous data (proportions). B. Chi-square test is also used for comparing categorical variables, not proportions. When comparing proportions, the Z-test is a better choice. C. Odds ratio is a measure of the strength of association between two categorical variables, not for comparing proportions directly. It can be used in conjunction with a test for proportions, but is not a test itself. D. Fisher's exact test is used when the expected count in any cell of a 2 x 2 table is less than 5. It is suitable when the assumptions of the Z-test are not met, such as for small sample sizes or unequal sample sizes. However, it is not suitable for large sample sizes and equal sample sizes (as in the given question). **Core Concept:** When dealing with large sample sizes and equal sample sizes, the Z-test is the appropriate test to determine if the difference between proportions is statistically significant. **Why the Correct Answer is Right:** The Z-test is suitable for large sample sizes and equal sample sizes because it provides a standardized measure of the difference between proportions, allowing for easier interpretation and comparison of the results. **Why Each Wrong Option is Incorrect:** A. Chi-square test assumes equal sample sizes and is not suitable for large sample sizes, making it unsuitable for this scenario. B. Odds ratio is a measure of association, not directly comparing proportions. It can be used in conjunction with a test for proportions but is not a test itself. C. Fisher's exact test is used when the expected count in any cell of a 2 x 2 table is less than 5. This test is suitable when the assumptions of the Z-test are not met, such as for small sample sizes or unequal sample sizes. However, it is not suitable for large sample sizes and equal sample sizes. **Core Concept:** Understanding when to use appropriate statistical tests is crucial for accurate interpretation and application of test results in clinical practice. **Why the Correct Answer is Right:** The Z-test is appropriate when dealing with large sample sizes and equal sample sizes, providing