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Past exam of the mathematics course of the University of Cambridge 2019 iii Paper 207 3 2 c Solution by
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MAR is plausible if clinic withdrawal is driven by recorded QoL, observed side effects, treatment, and other measured history. It is doubtful if patients leave because of an unrecorded deterioration, an imminent recovery, treatment toxicity not included in the analysis, or dissatisfaction that predicts their unseen 12-month QoL. The large dropout fraction makes such missing not at random mechanisms a serious concern, so MAR should be supported by rich predictors and sensitivity analysis rather than assumed without examination.
Past exam of the mathematics course of the University of Cambridge 2019 iii Paper 207 3 2 b Solution by
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In this trial, MAR means that among patients assigned the same treatment who have the same recorded QoL trajectory up to a visit, the probability of dropping out next is unrelated to what their later QoL values would have been. Dropout may depend strongly on previous poor QoL, treatment assignment, and other observed history; MAR only rules out residual dependence on the unobserved outcomes.
Past exam of the mathematics course of the University of Cambridge 2019 iii Paper 207 3 2 a Solution by
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Past exam of the mathematics course of the University of Cambridge 2019 iii Paper 207 2 2 4 Solution by
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The mediation estimate relies on several strong assumptions. Possible failures include mediator-outcome confounding, residual exposure-outcome or exposure-mediator confounding, and an exposure-induced mediator-outcome confounder. Smoking duration may itself be part of the causal pathway, making adjustment inappropriate. Self-reported cigarettes per day has measurement error and does not fully measure tobacco exposure. The case-control sampling can create selection bias; population stratification can confound the genotype relations; cancer may alter reported smoking; and the product-of-coefficients calculation can be inappropriate for a binary outcome because odds ratio effects are nonlinear and noncollapsible. Any of these can attenuate or distort the indirect effect.
Past exam of the mathematics course of the University of Cambridge 2019 iii Paper 207 2 2 3 Solution by
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The significant additive-scale interaction and the association of the variant with cancer among smokers but not nonsmokers indicate effect modification: the joint effect of genotype and smoking exceeds additivity on the risk scale. Under adequate control of confounding and selection, that pattern supports a causal role for smoking in activating or amplifying the genetic pathway. Interaction alone is not proof that smoking is causal, because smoking was not randomized and the stratum-specific estimates can be affected by confounding, selection, and low power among nonsmokers.
Past exam of the mathematics course of the University of Cambridge 2019 iii Paper 203 4 d ii Solution by
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Past exam of the mathematics course of the University of Cambridge 2019 iii Paper 203 4 d i Solution by
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Past exam of the mathematics course of the University of Cambridge 2019 iii Paper 203 3 d ii Solution by
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Write the semimartingale decomposition as , where is a continuous local martingale and has finite variation. Applying Itô formula to shows that its finite-variation part isIt vanishes for every . Multiplying by givesSubtract this identity for two points with distinct to obtain ; then . Since the curve starts at zero, . The Lévy characterization of Brownian motion now gives . Hence the Loewner chain is
Past exam of the mathematics course of the University of Cambridge 2019 iii Paper 203 3 d i Solution by
Codex 0 2026-10-03
Fix and writeBy assumption, is a continuous local martingale, so is a semimartingale. The Chordal Loewner equation giveswhich has finite variation. Thereforeis a semimartingale. Thus the Loewner driver is a continuous semimartingale.
Past exam of the mathematics course of the University of Cambridge 2019 iii Paper 203 3 c ii Solution by
Codex 0 2026-10-03
The imaginary partis a bounded local martingale and hence a martingale. As the simple transient trace passes , this angle converges to if the trace passes to the right of and to if it passes to the left. Bounded convergence therefore givesso the SLE4 left-passage probability is
Past exam of the mathematics course of the University of Cambridge 2019 iii Paper 203 3 c i Solution by
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Past exam of the mathematics course of the University of Cambridge 2019 iii Paper 203 2 c iii Solution by
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For compact , letBy the Tonelli theorem and part (ii),Every point in the SLE range has conformal radius tending to zero and therefore belongs to every . Hence the range inside has zero expected Lebesgue measure, and so has zero measure almost surely. Exhausting by countably many compact sets proves
Past exam of the mathematics course of the University of Cambridge 2019 iii Paper 203 2 c ii Solution by
Codex 0 2026-10-03
At time zero, . Compactness of givesAlso is uniformly bounded above on . Onone has . Optional stopping, Fatou lemma, and the assumed conditional angular estimate giveThusThe exponent requested in the question does not follow and is false as written. The SLE Green-function estimate gives probability comparable to , confirming that the denominator in the requested exponent should be .
Past exam of the mathematics course of the University of Cambridge 2019 iii Paper 203 2 c i Solution by
Codex 0 2026-10-03
Putso . Before , one has and . ThereforeThe supplied continuous local martingale is thus bounded after stopping, and a bounded local martingale is a true martingale. Hence
Past exam of the mathematics course of the University of Cambridge 2019 iii Paper 203 1 c iii Solution by
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It has the Loewner local growth property when, after mapping out the old hull, each short new increment is small: for every there is such thatEquivalent formulations use a crosscut of diameter below separating the new increment from infinity.
Past exam of the mathematics course of the University of Cambridge 2019 iii Paper 203 1 c ii Solution by
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It has the half-plane-capacity parameterization under the standard chordal convention when
Past exam of the mathematics course of the University of Cambridge 2019 iii Paper 203 1 c i Solution by
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Past exam of the mathematics course of the University of Cambridge 2019 iii Paper 203 1 b iii Solution by
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The statement is true. In the notation of part (ii), equality of the capacities forces . Every nonempty compact H-hull has strictly positive half-plane capacity: by the Brownian representation of half-plane capacity, Brownian motion started sufficiently high has positive harmonic measure of a boundary portion of positive height. Hence , so and
Past exam of the mathematics course of the University of Cambridge 2019 iii Paper 203 1 b ii Solution by
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Map out first. The imagewith its bounded filling is a compact H-hull, and uniqueness of hydrodynamic normalization givesComparing the coefficients of at infinity yields the half-plane-capacity composition ruleThus half-plane capacity is monotone under inclusion.
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