Purpose

Initial Rows: 500 observations entered the pipeline
Final Rows: 500 observations retained for analysis (100% retention rate)
Rows Removed: 0 - No data loss occurred during preprocessing
Data Quality: No filtering, imputation, or exclusion steps were applied

This section presents the Mann-Whitney U test results, a non-parametric statistical test appropriate for comparing two independent groups with non-normal distributions. It determines whether the ad and psa groups have statistically significantly different distributions, which is essential for validating whether observed differences are genuine rather than due to random variation.

Key Findings

Mann-Whitney U Statistic: 7807.50 - Represents the test statistic calculated from ranked data across both groups
P-Value: 0.0079 - Falls below the 0.05 significance threshold, indicating strong evidence against the null hypothesis
Statistical Significance: TRUE - The difference between groups is statistically significant at the 95% confidence level

Interpretation

The p-value of 0.0079 provides strong evidence that the ad and psa groups have meaningfully different distributions. This finding aligns with the descriptive statistics showing the ad group has a higher median (79 vs. 35) and greater spread. The Mann-Whitney U test was appropriately chosen because both groups failed normality tests (Shapiro-Wilk p-values near 0), making it more reliable than parametric alternatives.

Context

The severe sample size imbalance (475 ad vs. 25 psa observations) should be considered when interpreting results