How to answer this Technical interview question about Missing Data for Mid-Level Data Scientist?

How do you handle missing data in a dataset intended for machine learning?

Data Scientist

Technical

Asked at

IBM

Difficulty :

Medium

Explanation

This question evaluates your ability to preprocess datasets with missing values, which is crucial for building robust machine learning models. Recruiters assess your knowledge of imputation methods, handling missingness mechanisms, and trade-offs between these methods. Common pitfalls include failing to consider the type of missingness (e.g., MCAR, MAR, MNAR) or ignoring the impact on model performance. A strong answer includes justifying the chosen imputation method and considering its impact on the dataset.

Answer Example

I handle missing data by first analyzing the type of missingness (MCAR, MAR, or MNAR) and the percentage of missing values. For small amounts of missing data, I use simple imputation methods like mean or median for numerical features or mode for categorical features. For larger gaps, I apply advanced techniques like KNN imputation or model-based methods. For example, in a healthcare project, I used KNN imputation to handle 20% missing data in patient records, which preserved the dataset's integrity and improved model accuracy by 15%.

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