Purpose

This section documents the data cleaning and preparation phase for the chi-square independence test analyzing factors affecting test performance. Perfect retention indicates no rows were excluded during preprocessing, meaning the full dataset of 1,000 survey responses remained available for statistical analysis. This is critical for maintaining statistical power and ensuring the test results reflect the complete sample.

Key Findings

Retention Rate: 100% (1,000 of 1,000 rows retained) - No observations were removed during data cleaning, preserving the full analytical sample
Rows Removed: 0 - No missing values or data quality issues necessitated exclusion from the categorical variables analyzed
Data Integrity: Complete dataset available for all 10 variable pairs tested in the chi-square analysis

Interpretation

The perfect retention rate indicates robust data quality in the survey responses. Since the chi-square test requires complete cases for contingency table construction, maintaining all 1,000 observations strengthens the reliability of the statistical findings. The absence of missing data in categorical columns (gender, race/ethnicity, parental education, lunch program, test prep) means no information loss occurred that could bias association estimates or reduce statistical power.

Context

The analysis note mentions "Missing values in categorical columns" as a removal reason, yet zero rows were actually removed—suggesting either no missing values existed or they were handled through imputation rather than deletion