Interview Q&A / Data Science

1. How do you detect outliers using the IQR and z-score methods?

   With the IQR method, a value is an outlier if it lies below Q1 minus 1.5 times the IQR or above Q3 plus 1.5 times the IQR. With the z-score method, a value is flagged if it is more than about 3 standard deviations from the mean. IQR is more robust for skewed data and small samples, because outliers inflate the mean and standard deviation.

   IntermediateIn-depth4 min read
2. What is a z-score, and how does it help compare values on different scales?

   A z-score is (value - mean) / standard deviation, the number of standard deviations a value sits from the mean. Because it removes units and scale, you can compare a Maths mark with a Physics mark fairly.

   BeginnerQuick answer1 min read