AI0-001 Machine Learning and Deep Learning Practice Question
A machine learning engineer is building a spam filter. The dataset contains 10,000 emails, of which 1,000 are spam. The engineer decides to use a Random Forest classifier. Which preprocessing step is most critical to ensure the model generalizes well to new, unseen emails?
⚠ Common exam trap
CompTIA often tests the concept of data leakage by presenting preprocessing steps that seem harmless but actually incorporate test set information, tricking candidates into thinking scaling or dimensionality reduction is always necessary for tree-based models.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Split the data into training and testing sets before any other preprocessing
Splitting the data into training and testing sets before any other preprocessing prevents data leakage. If preprocessing like normalization or PCA is applied to the entire dataset first, the test set information influences the training process, leading to overly optimistic performance estimates and poor generalization to new, unseen emails.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Apply Principal Component Analysis (PCA) to reduce dimensionality
Why it's wrong here
PCA may discard useful information and is not necessary for Random Forest.
- ✗
Normalize the numerical features to have zero mean and unit variance
Why it's wrong here
Random Forest is not sensitive to feature scaling.
- ✓
Split the data into training and testing sets before any other preprocessing
Why this is correct
Splitting first prevents data leakage and ensures realistic evaluation.
- ✗
Encode all features using one-hot encoding
Why it's wrong here
One-hot encoding is not universally needed and may increase dimensionality unnecessarily.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This AI0-001 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the AI0-001 exam.