Interview Q&A / Data Science
Data Science interview questions
Statistics, pandas, cleaning data and exploratory analysis for analyst and data science roles.
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- 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 - What is the 68-95-99.7 rule for the normal distribution?
In a normal distribution, about 68% of values lie within 1 standard deviation of the mean, 95% within 2 and 99.7% within 3. It gives a fast way to judge how unusual a value is.
BeginnerQuick answer1 min read - When do you use the binomial distribution?
Use it to count successes in a fixed number of independent trials, each with the same probability of success. The probability of exactly k successes in n trials is C(n,k) p^k (1-p)^(n-k).
BeginnerQuick answer1 min read - How do you check whether data is normally distributed?
Look first: a histogram and a Q-Q plot, where points hugging the straight line suggest normality. Then optionally confirm with a test such as Shapiro-Wilk, remembering that large samples reject for tiny, harmless deviations.
IntermediateQuick answer1 min read - What does the exponential distribution model?
The exponential distribution models the waiting time until the next event when events arrive randomly at a constant rate. It is memoryless: the time already waited does not change the remaining wait.
IntermediateQuick answer1 min read - What is the Poisson distribution, and what kind of data does it model?
Poisson models the number of events in a fixed interval of time or space when events occur independently at a constant average rate. It has one parameter, the rate lambda, which is both its mean and its variance.
IntermediateQuick answer1 min read - Why are incomes and prices right-skewed, and why does a log transform help?
Such values grow by percentages rather than fixed amounts, so many small effects multiply and produce a long right tail (log-normal shape). Taking the log turns multiplication into addition and usually makes the data close to symmetric.
IntermediateQuick answer1 min read