Explicit Policy

What Missing Handling Is and Is Not

Close the boundary: this is an explicit preprocessing rewrite, not a model claim.

highlighted = computed this step

What missing-value handling does

It rewrites displayed missing cells using the pinned preprocessing policy so later methods receive explicit values and indicators.

missing cells→filled cells plus indicators\text{missing cells}\rightarrow\text{filled cells plus indicators}
Missing Values ExactlyExact missing-cell replacements from a pinned policy.explicit missing-value policyrowage rawcolor rawage filledcolor filledage_missingcolor_missingA2red2red00B?blue6blue10C6?6red01D10red10red00age mean: (2+6+10)/3 = 6color mode: red count 2, blue count 1add missingness indicatorsexplicit preprocessing policy for displayed missing cellsnumeric uses observed mean; categorical uses observed modemissingness indicators stay visibleNOT training; NOT learning; NOT generalizationNOT accuracy; NOT calibration; NOT a guarantee of model qualityNOT probability truth

What it does not do

It does not train a model and does not prove accuracy, calibration, model quality, or probability truth.

preprocessing only\text{preprocessing only}
Missing Values ExactlyExact missing-cell replacements from a pinned policy.explicit missing-value policyrowage rawcolor rawage filledcolor filledage_missingcolor_missingA2red2red00B?blue6blue10C6?6red01D10red10red00age mean: (2+6+10)/3 = 6color mode: red count 2, blue count 1add missingness indicatorsexplicit preprocessing policy for displayed missing cellsnumeric uses observed mean; categorical uses observed modemissingness indicators stay visibleNOT training; NOT learning; NOT generalizationNOT accuracy; NOT calibration; NOT a guarantee of model qualityNOT probability truth

The honest boundary

This book pins one missing-value policy. It is NOT training, NOT learning, NOT generalization, NOT accuracy, NOT calibration, NOT a guarantee of model quality, and NOT probability truth.

explicit policy; deferred claims explicit\text{explicit policy; deferred claims explicit}
Missing Values ExactlyExact missing-cell replacements from a pinned policy.explicit missing-value policyrowage rawcolor rawage filledcolor filledage_missingcolor_missingA2red2red00B?blue6blue10C6?6red01D10red10red00age mean: (2+6+10)/3 = 6color mode: red count 2, blue count 1add missingness indicatorsexplicit preprocessing policy for displayed missing cellsnumeric uses observed mean; categorical uses observed modemissingness indicators stay visibleNOT training; NOT learning; NOT generalizationNOT accuracy; NOT calibration; NOT a guarantee of model qualityNOT probability truth