Every question below was asked in a real UPSC ISS interview, drawn from the transcripts of recommended candidates across the last year cycles, lightly generalised. Each carries a one line pointer, not a full answer, because the thinking is the preparation.
Week 2 covered the machinery: the ISS officer’s work, the surveys, the indices, GDP, simple explanations and data current affairs. Day 14 is the test. Read each question aloud, answer aloud, then read the pointer. Tick a question only when your spoken answer would survive one follow up.
Core statistics
1. What is a distribution function, and where is it used in practice? Pointer: cumulative probability up to a point; think lifetimes, incomes, waiting times.
2. What is the value of the distribution function at zero for a symmetric distribution centred at zero? Pointer: half.
3. If X is normal with mean p and variance q, what is the distribution of aX plus b? Pointer: still normal; transform the mean and variance.
4. Does the binomial distribution have the additive property, and under what condition? Pointer: yes, when the success probability is common.
5. Why do so many quantities look normal as samples grow? Pointer: sums of many small independent effects; the central limit intuition, said simply.
6. Which is more serious, a Type 1 or a Type 2 error? Give an example. Pointer: it depends on costs; screening versus courtroom.
7. Mean, median or mode for income in India, and why? Pointer: median; skewness drags the mean.
8. What is the harmonic mean of 1 and 2, without paper? Pointer: four thirds; and the real test is composure.
9. What makes an estimator good, and how can a given estimator be improved? Pointer: unbiasedness, efficiency, consistency; conditioning on a sufficient statistic improves.
10. What are the components of a time series, and how would you begin modelling one? Pointer: trend, seasonality, cycle, irregular; plot first, always.
11. What is regression in one sentence a non statistician would accept? Pointer: the average way one thing changes when another does.
12. What is principal component analysis, and how do you choose the number of components? Pointer: new axes capturing maximum variance; keep enough variance explained.
13. Which statistical software do you know, and what have you actually done with it? Pointer: name only what you can demonstrate; one real project beats five listed tools.
Sampling and surveys
14. Design a sample survey of a given population, step by step. Pointer: objective, frame, design, size, instrument, fieldwork, estimation with errors.
15. Where is non probability sampling acceptable? Pointer: exploration and pilots, never national estimates.
16. Can exit polls be trusted? What survives even careful sampling? Pointer: non sampling error, especially response bias; representativeness is not the whole battle.
17. How is non response handled in surveys? Pointer: follow ups, reweighting, and specialised techniques exist; naming the problem precisely is most of the answer.
18. Which survey measures unemployment, and what changed in it recently? Pointer: PLFS; revamped from January 2025, monthly rural and urban bulletins.
19. Which survey underpins consumption and poverty measurement, and what else did it rebuild this year? Pointer: HCES; its 2023-24 round supplied the new CPI basket.
20. What is the Time Use Survey, and how does it connect to national accounts? Pointer: how people spend the day; unpaid household work that GDP does not count.
Official statistics and the economy
21. Name five or six official indices. Pointer: CPI, WPI, IIP, and the Labour Bureau’s worker CPIs make a comfortable list with room to spare.
22. What is the difference between IIP and WPI? Pointer: output volume versus wholesale price.
23. What changed in the new CPI series? Pointer: base 2024, HCES 2023-24 weights, 358 items, COICOP 2018, rural house rent, digital collection; released February 2026.
24. What is the difference between GNP and NDP? Pointer: net foreign income added versus depreciation subtracted, both starting from GDP.
25. What do ISS officers do, and which task matters most? Pointer: surveys, national accounts, prices, ministries, data quality; then choose one and defend it.
The close of Week 2
Count your honest ticks. Twenty or more, and your technical spine is ready; below fifteen, and this list is your revision plan for the weekend, with each pointer leading back to its full post earlier in the series.
Week 3 changes register one last time. The content is now in you; from tomorrow we work on the room itself: the first ninety seconds, the art of saying I do not know, opinion questions without landmines, and how to mock yourself at home before anyone mocks you officially.
For the free ISS Interview Starter Kit and the DAF Question Mapper, send the word INTERVIEW on WhatsApp to +91 842591 5355.
Frequently Asked Questions
What technical questions are asked in the ISS interview?
Core statistics such as distributions, estimation, errors and regression; sampling and survey design; and official statistics including PLFS, HCES, the CPI, GDP aggregates and the work of ISS officers. All twenty five questions above come from real transcripts.
How technical is the ISS interview compared to the written exam?
Far less deep but far more spoken. Boards test whether you can explain foundations simply and honestly, sometimes with small mental calculations, rather than solve written problems.
How should I revise technical topics for the ISS interview?
Answer real questions aloud, one line at a time, and follow each gap back to its topic. Spoken fluency on foundations beats silent depth on the frontier.
Practice. Improve. Repeat.