Interview Q&A / Data Science
Data Science interview questions
Statistics, pandas, cleaning data and exploratory analysis for analyst and data science roles.
Prefer rapid revision? Practise Data Science short interview answers →
- What are variance and standard deviation, and why do we need them?
Variance is the average of the squared distances from the mean, and standard deviation is its square root. They measure how spread out the data is. Two datasets can have the same mean but very different spread, and standard deviation is easier to read because it is in the same units as the data.
BeginnerIn-depth3 min read - What is the difference between mean, median and mode, and when is the median better?
The mean is the sum divided by the count, the median is the middle value after sorting, and the mode is the most frequent value. Use the median when the data is skewed or has outliers, like salaries, because one very large value pulls the mean up but barely moves the median.
BeginnerIn-depth4 min read - How do you read a box plot?
A box plot shows the median, Q1 and Q3 as a box, whiskers reaching the furthest points within 1.5 x IQR of the box, and dots for points beyond that. It summarises centre, spread, skew and outliers in one compact picture.
BeginnerQuick answer1 min read - What is a percentile, and how is it different from a quartile?
A percentile is the value below which a given percentage of the data falls. Quartiles are just three special percentiles: Q1 is the 25th, Q2 the 50th (the median) and Q3 the 75th.
BeginnerQuick answer1 min read - What is a weighted average, and when should you use it instead of a simple average?
A weighted average multiplies each value by its importance (weight) and divides by the total weight. Use it when items do not count equally, such as marks with different credit values or averaging group means of unequal size.
BeginnerQuick answer1 min read - What is skewness, and what does it tell you about the mean and median?
Skewness measures how lopsided a distribution is. In a right-skewed distribution a long tail of large values pulls the mean above the median; in a left-skewed one the mean falls below the median.
BeginnerQuick answer1 min read - Why is the range a weak measure of spread?
The range is maximum minus minimum, so it depends only on the two most extreme values. One outlier can change it enormously while the rest of the data is unchanged, which makes it unstable. IQR or standard deviation use more of the data.
BeginnerQuick answer1 min read