Purpose

This section documents the data preprocessing pipeline for the ANCOVA analysis comparing four therapy types. Perfect data retention (100%) indicates no rows were removed during cleaning, meaning all 500 observations proceeded to statistical analysis without exclusions or transformations. This is critical for understanding whether the final results represent the complete dataset or a filtered subset.

Key Findings

Initial Rows: 500 observations entered the preprocessing pipeline
Final Rows: 500 observations retained after cleaning (100% retention rate)
Rows Removed: 0 — no observations were excluded during data quality checks
Data Integrity: No missing values, duplicates, or outliers triggered removal; the assumption tests confirmed 0 outliers using studentized residuals (|studentized| > 3)

Interpretation

The perfect retention rate suggests either exceptionally clean source data or minimal preprocessing criteria applied. This is consistent with the ANCOVA results, where no outliers were detected and all 500 cases contributed to the F-statistic (F=0.324, p=0.808). The complete dataset strengthens statistical power for detecting group differences, though the negligible effect size (partial η²=0.002) reflects genuine similarity between therapy types rather than data limitations.

Context

No train/test split was performed, indicating this is a confirmatory analysis rather than predictive modeling.