Random Forest and XGBoost for Mobile-Number Validity Classification
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Abstract
Invalid mobile numbers in registration forms cause failed notifications, and a deterministic validator catches only the cases its rules cover. This study asks whether ensemble classifiers can learn a validity rule from syntactic features, and which does it better. We built a dataset of 46,485 Indonesian numbers and labeled them by rule: prefix 08, 10–13 digits, and an allocation list for the first four digits (8.68% invalid). Random Forest and XGBoost were trained after SMOTE on 37,188 records and tested on 9,297 untouched records (807 invalid). With a binary prefix-validity flag supplied (scenario 1), both models made 53–54 errors (about 99.4% accuracy). With the third and fourth digits as numeric features instead (scenario 2), XGBoost made 9 errors (99.90%) and Random Forest 75 (99.19%); exact bounds show the difference is significant under any overlap of errors (p < 10^−13). XGBoost also trained about 36 times faster, on undocumented hardware. Because the labels come from rules that the features reproduce, the accuracies measure rule recovery, not detection of well-formed but wrong numbers; no independent ground truth or rule-based baseline was evaluated. The results support XGBoost as a learned approximation of the rule and call for validation against verified contact status.
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