Interview practice

Data Scientist / ML Engineer

0–2 years · Junior — Python · Statistics · scikit-learn · Feature engineering · Model evaluation · Deployment

0–2 years 2–5 years 5–8 years 8+ years
ownership Feature engineering challenges 1 of 6
Can you tell me about a situation where a feature you created did not contribute positively to your model? How did you handle it?
What a strong answer covers

Mentions a specific feature and its intended impact; describes the evaluation process that revealed its ineffectiveness; includes how feedback was gathered from stakeholders or team members; explains the steps taken to modify or remove the feature; reflects on lessons learned regarding feature importance.

The follow-up you would get

What indicators would you look for earlier next time?

Could you have answered that?
technical Model Evaluation 2 of 6
A model evaluation shows a high precision but low recall. What does this indicate about the model's performance, and what actions might you take?
What a strong answer covers

Indicates the model is good at predicting positive cases but misses many; considers adjusting the classification threshold to improve recall; explores techniques like F-beta score for balanced performance evaluation; examines feature importance to identify potential improvements; investigates additional data for the minority class.

The follow-up you would get

What is the effect of changing the classification threshold on precision and recall?

Could you have answered that?
technical Deployment 3 of 6
You need to deploy a machine learning model with a requirement for low latency responses. What considerations do you take into account regarding the model and its environment?
What a strong answer covers

Assesses model complexity versus performance trade-offs; optimises the model for inference, possibly using techniques like quantisation or pruning; configures a fast serving infrastructure such as a REST API; monitors latency and throughput during and after deployment; prepares to scale the model serving if needed.

The follow-up you would get

What is model quantisation and why is it used?

Could you have answered that?
ownership A deployment issue 4 of 6
Describe a time when you deployed a model and it did not perform as expected. What did you learn from that experience?
What a strong answer covers

Identifies a specific model and deployment context; explains the performance metrics that dropped and how they were measured; describes the investigation process, including monitoring logs and data drift; outlines what corrective actions were taken and their impact; reflects on the importance of pre-deployment testing.

The follow-up you would get

What would you do differently in future deployments?

Could you have answered that?
scenario Metric Choice 5 of 6
You are asked to choose metrics for a model that predicts rare events, and stakeholders have conflicting priorities. How do you approach this decision?
What a strong answer covers

Identifies key stakeholders and their priorities; evaluates precision, recall, and F1 score for alignment with business goals; suggests creating a precision-recall curve to visualise trade-offs; discusses implications of different metrics on model behaviour; proposes a balanced scorecard to meet diverse needs.

The follow-up you would get

How do you handle a situation where the chosen metric does not seem to reflect real-world performance?

Could you have answered that?
technical Statistics 6 of 6
You are observing that a model gives different predictions on the same data when run on different machines. What could be the cause, and how do you investigate this issue?
What a strong answer covers

Checks for version discrepancies in libraries such as scikit-learn or NumPy; verifies the randomness in train-test splits or initialisation of model parameters; inspects for differences in data preprocessing steps; considers the environment setup including hardware differences; confirms consistent seed settings for reproducibility.

The follow-up you would get

What role does random seed play in model training?

Could you have answered that?
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