Past exam of the mathematics course of the University of Cambridge 2016 iii Paper 207 1 c Solution Created 2026-10-03 Updated 2026-10-06
Let denote the centered unit-variance bivariate normal distribution density,The complement of rejecting either null hypothesis is . Therefore the probability of at least one rejection isWhen both null hypotheses are true, this is the familywise error rate. If one null hypothesis is false, a rejection of that hypothesis is not a Type I error, so the displayed probability is then an any-rejection probability rather than the familywise error rate.
Past exam of the mathematics course of the University of Cambridge 2016 iii Paper 207 1 d Solution Created 2026-10-03 Updated 2026-10-06
Couple the Wald test statistics as , where the joint centered bivariate normal distribution of is fixed. Increasing either enlarges, pointwise in this coupling, the event . Its probability is consequently nondecreasing in each treatment effect.
If both null hypotheses hold, then , so this probability is maximal at the joint boundary . To check the familywise error rate across all configurations, suppose only hypothesis is true. A Type I error then occurs only if , with probability at most , where is the standard normal distribution function. This is no larger than the any-rejection probability at , since that joint event contains . If neither null hypothesis is true, the familywise error rate is zero. Hence the least-favourable null configuration for Type I error iswhere is the centered bivariate normal distribution function with correlation coefficient .
Past exam of the mathematics course of the University of Cambridge 2016 iii Paper 210 1 a Solution Created 2026-10-03 Updated 2026-10-06
For each ball, the event of landing in is a Bernoulli distribution trial. Under the null hypothesis its probability is . Under the selected alternative , its probability is . The placements are independent random variables conditional on that selected index, so the count has the binomial distribution:The second assertion concerns , rather than the unconditional mixture model .
Past exam of the mathematics course of the University of Cambridge 2016 iii Paper 210 1 c Solution Created 2026-10-03 Updated 2026-10-06
Put and . Use the scan statistic and the statistical hypothesis testing ruleThe union bound and the Hoeffding inequality give , since . Conditional on index , accepting the null hypothesis implies . The assumed separation gives , so this threshold lies more than below the alternative expected value . The lower-tail Hoeffding inequality therefore gives . Averaging the conditional error over the mixture model gives as well.
Past exam of the mathematics course of the University of Cambridge 2016 iii Paper 210 2 c Solution Created 2026-10-03 Updated 2026-10-06
Put and . Use the quadratic scan statistic and reject when . Under the null hypothesis, each has the chi-squared distribution with degrees of freedom. The chi-squared concentration inequality gives , by the union bound. Since , the proposed Type I error is at most .
For the true set , has the same chi-squared distribution. We need a lower-tail bound that remains positive even when is close to one. Set . The chi-squared Chernoff lower-tail bound gives : indeed for . To verify this last inequality, its derivative is ; the expression in parentheses is strictly concave, starts at zero, and changes sign once, so the minimum occurs at an endpoint, where the inequality holds.
The function is convex with , so on this interval. Consequently implies . Failure to reject then requires , giving Type II error at most , uniformly in . An explicit, deliberately conservative answer isThe sharp constant is unnecessary; the detection scale is .
Past exam of the mathematics course of the University of Cambridge 2017 ib Paper 4 19H b Solution Created 2026-09-24 Updated 2026-10-05
Under the null hypothesis , has the uniform distribution on . Against , the likelihood ratio is , increasing on that interval. The Neyman-Pearson lemma therefore givesThe size of a statistical test is , and there is no boundary randomisation issue for this continuous probability distribution. Its statistical power against is .
For every admissible alternative , the likelihood ratio is strictly increasing. The same upper-tail rejection set has size and is a most powerful test against each fixed such alternative, again by the Neyman-Pearson lemma. Hence the same test is a uniformly most powerful test against , where the alternative is understood within the specified parameter range. Its full power function isFor or , the never-reject or always-reject test supplies the respective endpoint case.
Past exam of the mathematics course of the University of Cambridge 2017 iii Paper 205 3 Solution Created 2026-10-03 Updated 2026-10-05
Let denote the number of rejected null hypotheses and the number of rejected true null hypotheses. The familywise error rate is , whereas the false discovery rate is , with a zero contribution when . A valid true-null p-value satisfies for .
For the closed testing procedure, choose a level- local test of every nonempty intersection . Reject only if every intersection containing it is rejected by its local test. If any true null hypothesis is rejected, the local test of must reject. Since that intersection is true, its rejection probability is at most . If is empty there can be no false rejection. This proves strong closed-testing control of the familywise error rate, under arbitrary dependence, provided each local test is valid under its whole intersection null.
For the Benjamini-Hochberg procedure, order the p-values and setwith maximum zero if the set is empty; reject the first hypotheses. To prove its false discovery rate bound, fix a true-null index . Replace by zero and let be the modified rejection count. This is a function of the other p-values and satisfies .
The Benjamini-Hochberg leave-one-out identity isHere is its deterministic justification. If was rejected, lowering its value cannot decrease , and leaves all ordered values of ranks greater than unchanged. No such rank can newly satisfy its threshold, so . Conversely, if and , at least other values and are at most this threshold. Therefore the original procedure has . Monotonicity under decreasing also gives , so and is rejected. This establishes the identity; harmless deterministic tie-breaking also covers the artificial zero introduced in the modified data.
The assumed independence makes independent of . Conditional on , validity of the p-value impliesSum over to obtainIf true-null p-values are exactly uniform rather than merely valid, the first inequality is equality. No restriction on dependence among the false-null p-values is needed beyond their joint independence from the true-null values.
For the requested Simes inequality, apply this result to the true-null p-values alone, for . Every rejection is now false, so and the false discovery rate is the probability of any rejection. The event of at least one Benjamini-Hochberg procedure rejection is exactlyIts probability is at most . This holds for ; with no true nulls the written minimum and division by are undefined and the error-control statement is instead vacuous.
The final step-up rule is the Hochberg procedure. Use Simes tests as the local tests for a closed testing procedure: reject when . Under any true intersection all its p-values are valid and independent, so the Simes inequality proves level for its local test. The implication supplied in the question says that whenever the Hochberg procedure rejects , every intersection containing passes its local Simes test. Thus every such rejection is also a closed-testing rejection. ConsequentlyThe true-null independence assumption is essential to this particular proof of local-test validity; the arbitrary-dependence guarantee of closed testing does not create valid local tests automatically.
Past exam of the mathematics course of the University of Cambridge 2017 iii Paper 207 1 c Solution Created 2026-10-03 Updated 2026-10-05
Under the null hypothesis of consistency, has approximately zero expectation and variance , since the displayed trials are independent. Thus a two-sided Wald test usesThe observed difference is , and . Its two-sided p-value is approximately , so there is no detectable discrepancy here. Failure to reject is not proof of consistency: this test has limited statistical power, and transitivity in network meta-analysis also needs substantive assessment. If evidence sources overlap, replace by .
Past exam of the mathematics course of the University of Cambridge 2017 iii Paper 207 2 a i Solution Created 2026-10-03 Updated 2026-10-05
A Type I error is rejecting a true null hypothesis. Here it means declaring a statistical association between the biomarker and bowel cancer when, in the population and under the association model being tested, there is no statistical association. It is a false positive association finding, not merely a large estimation error. A test with level limits this probability to under the null hypothesis, subject to valid calibration; the p-value is not the probability that the null hypothesis is true.
Past exam of the mathematics course of the University of Cambridge 2017 iii Paper 207 3 c iii Solution Created 2026-10-03 Updated 2026-10-05
Use one joint hypothesis test for . Fit the unrestricted model with statistical parameters , where and for treatment indicator . Refit under , estimating the two common baseline intensities; do not fix them at their unrestricted estimates. The likelihood-ratio test statistic isUnder regular identifiable positive-rate models, sufficient independent patient trajectories, and the null hypothesis, Wilks theorem gives two degrees of freedom because two coefficients are constrained. Reject if exceeds the chosen upper chi-squared distribution quantile. Alternatively a two-dimensional Wald test uses , including the off-diagonal covariance. Two separate tests do not provide this single calibrated assessment. The point estimates alone cannot produce a numerical p-value without fitted likelihoods or a coefficient covariance matrix.
Past exam of the mathematics course of the University of Cambridge 2017 ii Paper 2 5J a Solution Created 2026-09-24 Updated 2026-10-05
Use the usual normal linear model , with fixed full-column-rank design , , and . These Gaussian distribution and constant-variance hypotheses are necessary for an exact finite-sample Student's t-test. Put and . The vector of ordinary least squares estimators satisfiesWith , the test statistic isUnder the null hypothesis, has Student's t-distribution with degrees of freedom. A two-sided level- Student's t-test rejects when . If the intended test is one-sided against , it rejects when ; the statistical power conclusion below holds for either convention.
Past exam of the mathematics course of the University of Cambridge 2018 ib Paper 2 8H Solution Created 2026-09-24 Updated 2026-10-03
A simple hypothesis specifies a single probability distribution. For a test with rejection region , its size of a statistical test is the rejection probability under the simple null hypothesis, while its statistical power against the simple alternative is the rejection probability under that alternative. The Neyman-Pearson lemma states that among tests of size at most , a test rejecting for the largest values of the likelihood ratio has greatest power, with boundary randomization if needed.
Past exam of the mathematics course of the University of Cambridge 2018 ib Paper 3 20H Solution Created 2026-09-24 Updated 2026-10-03
Under the null hypothesis that treatment and recovery are independent, estimate each expected cell count byand form the Pearson chi-squared test of independence statistic . For a table its asymptotic null law is a chi-squared distribution with one degree of freedom. A second-order Taylor expansion of the generalized likelihood-ratio test statistic around the fitted counts gives this Pearson statistic, which explains its asymptotic null distribution.
Writing the four residuals over their fitted counts and simplifying givesFor ,whose one-degree-of-freedom p-value is about . There is no evidence of an effect. One fitted count is only , however, so the chi-squared approximation is questionable; Fisher's exact test would be preferable.
Past exam of the mathematics course of the University of Cambridge 2019 ii Paper 1 13J c Solution Created 2026-09-24 Updated 2026-09-29
The null hypothesis is that price and score are independent, equivalently that the independence log-linear model for a two-way contingency table is correct. Against the saturated alternative, the reported Poisson deviance is the likelihood-ratio test statisticUnder the null and the usual large-sample regularity assumptions, Wilks theorem givesThe observations must be independent, the cell probabilities must not lie on the boundary of the parameter space, and the expected counts must be large enough for the chi-squared asymptotic approximation. The fitted counts are either or , so the customary expected-count check is comfortably satisfied. Since(equivalently, the p-value is about ), we do not reject the null at the significance level. The data provide no significant lack of fit for independence.