ASRB NET and ARS / SMS / STO (Agricultural Scientists Recruitment Board) · India · Agricultural Scientists Recruitment Board
Original practice questions written to the published syllabus · not past papersThe statistics a veterinarian needs to read a paper, design a trial or analyse herd records: descriptive statistics, tests of significance, regression and experimental design.
In the exams: ICAR AIEEA-PG 14 (statistics unit); ASRB NET
How our questions for ASRB NET and ARS / SMS / STO spread across the units of Biostatistics, Computer Application & Research Methodology. Difficulty: 40 easy, 52 medium, 29 hard.
| Tests of significance: the t-test | 12 | |
| Research methodology | 12 | |
| Correlation and regression | 11 | |
| Measures of central tendency | 10 | |
| Probability distributions | 10 | |
| Analysis of variance | 10 | |
| Experimental designs: CRD and RBD | 10 | |
| Computer and spreadsheet basics | 10 | |
| Measures of dispersion | 9 | |
| Sampling methods | 9 | |
| The chi-square test | 9 | |
| Sample-size calculation | 9 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
Herd A has mean daily milk yield 10 litres with SD 2 litres; herd B has mean 25 litres with SD 4 litres. Which statement about relative variability is correct?
D. Herd A is relatively more variable, CV 20% against 16%
CV = SD/mean × 100: herd A 2/10 = 20%, herd B 4/25 = 16%. The larger SD of herd B reflects its larger mean; the unit-free CV shows herd A is relatively more variable.
Further reading: Petrie A, Watson P. Statistics for Veterinary and Animal Science, 3rd ed.
Every PCV reading from a mis-calibrated centrifuge is 3 percentage points too high. When 3 is subtracted from every reading, how do the mean and SD change?
B. Mean falls by 3; SD is unchanged
Subtracting a constant shifts the whole distribution (change of origin): the mean falls by 3, but every deviation from the mean is unchanged, so the SD and variance are unchanged. Multiplying by a constant would change the SD.
Further reading: Petrie A, Watson P. Statistics for Veterinary and Animal Science, 3rd ed.
Assuming each calf is equally likely to be male or female and births are independent, what is the probability that exactly 2 of 4 calves are female?
B. 0.375
Binomial: 4C2 × 0.5² × 0.5² = 6/16 = 0.375. 0.500 confuses 'half the calves' with a probability; 0.0625 is the probability of one specific order such as FFMM; 0.250 counts 4 orders instead of 4C2 = 6.
Further reading: Petrie A, Watson P. Statistics for Veterinary and Animal Science, 3rd ed.
In a normal distribution, approximately what percentage of observations lie within one standard deviation of the mean?
C. 68.27%
Mean ± 1 SD contains 68.27%, ± 2 SD 95.45% and ± 3 SD 99.73%. Exactly 95% lies within ± 1.96 SD.
Further reading: Petrie A, Watson P. Statistics for Veterinary and Animal Science, 3rd ed.
At α = 0.05, what is the critical value of z for a one-tailed test?
B. 1.645
One-tailed 5% puts all 5% in one tail: z = 1.645. 1.960 is two-tailed 5%; 2.576 two-tailed 1%; 2.326 one-tailed 1%.
Further reading: Petrie A, Watson P. Statistics for Veterinary and Animal Science, 3rd ed.
Two diagnostic tests are applied to the same 200 sheep. Which test compares the proportions positive by the two methods?
A. McNemar's test using the discordant pairs
Results on the same animals are paired, so McNemar's test applies: χ² = (b − c)²/(b + c), using only sheep positive on one test and negative on the other. An ordinary chi-square treats the two sets of results as independent samples.
Further reading: Thrusfield M, Christley R. Veterinary Epidemiology, 4th ed.
In a logistic regression of calf mortality on colostrum feeding, the coefficient for 'no colostrum within 6 hours' is 0.693. What does this mean?
D. Odds of death are doubled
In logistic regression, exp(coefficient) is the odds ratio: e^0.693 = 2.0, so the odds of death are twice as high. The coefficient is on the log-odds scale, not a probability or a percentage change in risk.
Further reading: Dohoo I, Martin W, Stryhn H. Veterinary Epidemiologic Research, 2nd ed.
In a 2 × 2 factorial trial, a feed additive improves growth at the low protein level but not at the high protein level. This is an example of:
C. Interaction between the two factors
Interaction exists when the effect of one factor depends on the level of the other. Factorial designs are the only designs that estimate it; separate one-factor trials miss it.
Further reading: Gomez KA, Gomez AA. Statistical Procedures for Agricultural Research, 2nd ed.
What is the main purpose of randomisation in an experiment?
C. To remove bias and make the error estimate valid
Randomisation gives every animal the same chance of each treatment, so unknown factors are not systematically linked to treatment and the error estimate is valid. It does not guarantee exactly equal groups; blocking addresses known differences.
Further reading: Gomez KA, Gomez AA. Statistical Procedures for Agricultural Research, 2nd ed.
Which study design starts with diseased and non-diseased animals and looks back at their past exposures?
D. Case-control study
A case-control study selects on outcome and compares past exposure, giving an odds ratio. A cohort study selects on exposure and follows forward; a cross-sectional survey measures both at one time.
Further reading: Petrie A, Watson P. Statistics for Veterinary and Animal Science, 3rd ed.
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