Summarize samples with center (mean, median), spread (variance, IQR), and shape (skew, outliers).
Center and spread
- Mean — sensitive to outliers
- Median — robust middle value
- Standard deviation — typical distance from mean
- IQR — middle 50% spread; basis for outlier rules
Percentiles
P95 latency means 95% of requests are faster—common SLA language. Report percentiles for skewed metrics (income, latency).
Important interview questions and answers
- Q: Mean vs median?
A: Median better when outliers skew mean. - Q: P95?
A: 95th percentile—only 5% of values are higher.
Self-check
- When prefer median over mean?
- What does standard deviation measure?
Tip: Report median with mean when distributions are skewed.
Interview prep
- Median vs mean?
Median robust to outliers; mean sensitive.
- P95?
95th percentile—5% of values exceed it.