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CUET-PG Nonparametric & Rank-Based Methods: practice questions

CUET-PG - Statistics · India · National Testing Agency

Original practice questions written to the published syllabus · not past papers
10worked here, free
69written to this exam in this subject
11syllabus units

What this subject covers

Methods that hold without a normal model: the empirical distribution, goodness-of-fit, sign and rank tests for one, two and many samples, rank correlation, and tests used for scored or ranked agricultural data such as disease ratings and sensory panels.

In the exams: AICE-JRF Ag Stat Unit 2 (heavy: run, sign, rank, Wilcoxon, Kruskal-Wallis, Mann-Whitney, Cochran, Friedman named); GATE ST 'Non-parametric Statistics' (heavy); UPSC ISS Statistics II (present)

Where the 69 questions fall

How our questions for CUET-PG spread across the units of Nonparametric & Rank-Based Methods. Difficulty: 31 easy, 29 medium, 9 hard.

Mann-Whitney U test and two-sample Kolmogorov-Smirnov test9
Goodness of fit: chi-square and Kolmogorov-Smirnov tests7
Friedman's test for randomised blocks7
Asymptotic relative efficiency7
Empirical distribution function and its properties6
Sign test and Wilcoxon signed-rank test6
Kruskal-Wallis test6
Spearman's and Kendall's rank correlations6
Analysing ordinal scores: disease ratings and sensory panels6
Run test for randomness5
Cochran's Q test4

10 practice questions, worked

Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.

1 · Goodness of fit: chi-square and Kolmogorov-Smirnov tests · medium

Which statement compares Pearson's chi-square and the Kolmogorov-Smirnov goodness-of-fit tests correctly?

  1. KS ignores the order of the classes; chi-square uses that order in its statistic
  2. KS uses ungrouped continuous data; chi-square suits counts and grouped data
  3. Chi-square needs a fully specified F₀; KS allows estimated parameters
  4. Chi-square is exact in small samples; KS is only an approximation
Answer and working

B. KS uses ungrouped continuous data; chi-square suits counts and grouped data

KS is exact and distribution-free for continuous, fully specified F₀ and avoids grouping. Chi-square handles discrete data and estimated parameters (with df adjustment) but loses information by grouping and ignores the order of classes.

Further reading: Gibbons and Chakraborti, Nonparametric Statistical Inference; Conover, Practical Nonparametric Statistics; Hollander, Wolfe and Chicken, Nonparametric Statistical Methods

2 · Goodness of fit: chi-square and Kolmogorov-Smirnov tests · easy

In a chi-square goodness-of-fit test of insect counts, several classes have expected frequencies below 5. What is the usual remedy?

  1. Replace the chi-square test by a t-test on the class frequencies
  2. Pool adjacent classes, then count df after pooling
  3. Add 0.5 to every observed count and keep all of the classes
  4. Drop those classes from the table and keep the original degrees of freedom
Answer and working

B. Pool adjacent classes, then count df after pooling

Small expected counts make the χ² approximation unreliable; adjacent classes are pooled and the df counted on the pooled classes. Dropping classes discards data and biases the test.

Further reading: Gibbons and Chakraborti, Nonparametric Statistical Inference; Conover, Practical Nonparametric Statistics; Hollander, Wolfe and Chicken, Nonparametric Statistical Methods

3 · Run test for randomness · easy

In a runs test for randomness, what do far too many runs suggest?

  1. Clustering of like symbols or a trend in the series
  2. Unequal variances
  3. A shift in location
  4. Alternation or negative dependence
Answer and working

D. Alternation or negative dependence

Many short runs mean the two symbols alternate more than chance allows, as with regular spacing or negative serial correlation. Too few runs indicate clustering or trend.

Further reading: Gibbons and Chakraborti, Nonparametric Statistical Inference; Conover, Practical Nonparametric Statistics; Hollander, Wolfe and Chicken, Nonparametric Statistical Methods

4 · Run test for randomness · medium

What is a weakness of the Wald-Wolfowitz two-sample runs test compared with the Mann-Whitney test?

  1. It cannot detect differences in spread
  2. It is valid only for equal sample sizes
  3. It needs normally distributed data
  4. Low power against a pure location shift
Answer and working

D. Low power against a pure location shift

The runs test reacts to any difference in distribution, but for a location shift Mann-Whitney is much more powerful. Neither needs normality, and the runs test does detect spread differences.

Further reading: Gibbons and Chakraborti, Nonparametric Statistical Inference; Conover, Practical Nonparametric Statistics; Hollander, Wolfe and Chicken, Nonparametric Statistical Methods

5 · Sign test and Wilcoxon signed-rank test · easy

What does the Wilcoxon signed-rank test assume about the distribution of the paired differences that the sign test does not?

  1. Symmetry of the differences
  2. Normality
  3. A known median
  4. Equal variances in the two members of each pair
Answer and working

A. Symmetry of the differences

Both need independence and continuity; the signed-rank test also assumes symmetry, which is what lets each rank carry either sign with probability 1/2. Neither assumes normality.

Further reading: Gibbons and Chakraborti, Nonparametric Statistical Inference; Conover, Practical Nonparametric Statistics; Hollander, Wolfe and Chicken, Nonparametric Statistical Methods

6 · Mann-Whitney U test and two-sample Kolmogorov-Smirnov test · easy

Two independent samples have sizes 6 and 6, and sample 1's rank sum is W₁ = 25. What is the Mann-Whitney statistic U₁?

  1. 4
  2. 11
  3. 25
  4. 14
Answer and working

A. 4

U₁ = W₁ − n₁(n₁ + 1)/2 = 25 − 21 = 4. U₂ = n₁n₂ − U₁ = 32. 14 = 25 − 11 omits the correct offset.

Further reading: Gibbons and Chakraborti, Nonparametric Statistical Inference; Conover, Practical Nonparametric Statistics; Hollander, Wolfe and Chicken, Nonparametric Statistical Methods

7 · Mann-Whitney U test and two-sample Kolmogorov-Smirnov test · medium

Six treated and six untreated plants are scored for disease; the Mann-Whitney U for the treated group is 4. What is the normal-approximation Z, ignoring ties and continuity correction?

  1. −4.67
  2. −2.72
  3. −2.24
  4. −0.359
Answer and working

C. −2.24

E(U) = 36/2 = 18, Var(U) = 36 × 13/12 = 39, Z = (4 − 18)/√39 = −2.24. Using 36/4 as the variance gives −4.67.

Further reading: Gibbons and Chakraborti, Nonparametric Statistical Inference; Conover, Practical Nonparametric Statistics; Hollander, Wolfe and Chicken, Nonparametric Statistical Methods

8 · Kruskal-Wallis test · hard

For k = 2 groups, how is the Kruskal-Wallis H related to the Mann-Whitney test?

  1. They are unrelated statistics
  2. H is half the Mann-Whitney U
  3. H equals the Mann-Whitney U itself, unstandardised
  4. H equals the square of the Mann-Whitney Z
Answer and working

D. H equals the square of the Mann-Whitney Z

With two groups H is the squared standardised rank-sum statistic, Z², and χ²₁ is the distribution of Z² for normal Z.

Further reading: Gibbons and Chakraborti, Nonparametric Statistical Inference; Conover, Practical Nonparametric Statistics; Hollander, Wolfe and Chicken, Nonparametric Statistical Methods

9 · Friedman's test for randomised blocks · easy

Which design is Friedman's test intended for?

  1. A completely randomised design with unequal group sizes
  2. A paired comparison of binary outcomes
  3. An RCBD with one observation per treatment per block
  4. A two-sample comparison of independent groups
Answer and working

C. An RCBD with one observation per treatment per block

Friedman ranks treatments within blocks, the rank analogue of the RCBD ANOVA. Binary blocked data use Cochran's Q.

Further reading: Gibbons and Chakraborti, Nonparametric Statistical Inference; Conover, Practical Nonparametric Statistics; Hollander, Wolfe and Chicken, Nonparametric Statistical Methods

10 · Analysing ordinal scores: disease ratings and sensory panels · hard

How is the Mann-Whitney test related to the proportional-odds model for comparing two groups on an ordinal scale?

  1. It is closely related to the score test for the group effect in that model
  2. It is unrelated, because the model is parametric and the test is not
  3. It is identical to the Wald test for the cut-point parameters θⱼ
  4. It is the likelihood-ratio test of the proportional-odds assumption itself
Answer and working

A. It is closely related to the score test for the group effect in that model

For two groups, the score test of β = 0 in the cumulative logit model is essentially the Wilcoxon rank-sum test with mid-ranks, which is why the two usually agree; the model adds odds-ratio estimates and covariates.

Further reading: Gibbons and Chakraborti, Nonparametric Statistical Inference; Conover, Practical Nonparametric Statistics; Hollander, Wolfe and Chicken, Nonparametric Statistical Methods

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Nonparametric & Rank-Based MethodsThe full study manual, free CUET-PGFormat, sections and how it has changed

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Nonparametric & Rank-Based Methods for other exams

GATE · IndiaIIT JAM · IndiaICAR AICE-JRF/SRF · IndiaIndian Statistical Institute admission tests · IndiaASRB NET · IndiaState statistical services · IndiaCSIR-UGC NET · IndiaASRB Agricultural Research Service · IndiaIndian Statistical Service Examination · IndiaICAR AIEEA-PG · IndiaSSC Combined Graduate Level · India

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