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The process by which certain pulses are emitted in a human body is modeled as a Poisson process. In other words, the times 𝑌 𝑚 between adjacent pulses are i.i.d. random variables which are exponentially distributed with the arrival rate 𝜆 . A healthy patient is characterized by the rate 𝜆 0 , while an unhealthy one is characterized by 𝜆 1 < 𝜆 0 . 𝑀 measurements of inter-pulse times are taken from a patient, and a healthy/unhealthy decision has to be made. However, the values of 𝜆 0 and 𝜆 1 are not known as they are in fact random. Specifically, each is assumed to be exponentially distributed, 𝜆 0 with mean value 𝜆 ¯ 0 , and 𝜆 1 with mean value 𝜆 ¯ 1 . With this model, the likelihood ratio is replaced by the Bayesian factor. The decision threshold is set to 𝜂 = 𝑃 0 𝑃 1 𝐶 𝑓 𝑎 𝐶 𝑚 𝑑 = 1 . 𝑀 = 10 observations are made on a patient, yielding the measured values 𝑦 1 , … 𝑦 𝑀 . If 𝜆 ¯ 0 = 1 and 𝜆 ¯ 1 = 𝜆 ¯ 0 / 4 , which of the following represents the Bayesian decision rule (numbers are rounded):
Options
A.∑
𝑚
=
1
10
𝑦
𝑚
𝐻
1
≷
𝐻
0
21.3
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Step-by-Step Analysis
Question restatement: We are modeling inter-pulse times Y_m as i.i.d. exponential with rate lambda. Healthy (H0) has rate lambda0, unhealthy (H1) has rate lambda1 < lambda0. Both rates are themselves random, each with an exponential prior: lambda0 ~ Exp(mean lambda0_bar) and lambda1 ~ Exp(mean lambda1_bar). The threshold is set such that the Bayes factor (or Bayesian decision statistic) uses a certain rule. With M = 10 observations y1,...,y10 and lambda0_bar = 1, lambda1_bar = lambda0_bar/4 = 0.25, the proposed decision rule is based on the sum S = sum_{m=1}^{10} y_m and a numeric cutoff (here 21.3, rounded). The question asks which representation corresponds to the Bayesian decision rule, with the given options.
Option analysis:
- Option: ∑_{m=1}^{10} y_m H1 ≷ H0 21.3
This option encodes a decision rule that compares the s......Login to view full explanationLog in for full answers
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The process by which certain pulses are emitted in a human body is modeled as a Poisson process. In other words, the times Ym between adjacent pulses are i.i.d. random variables which are exponentially distributed with the arrival rate λ. A healthy patient is characterized by the rate λ0, while an unhealthy one is characterized by λ1<λ0. M measurements of inter-pulse times are taken from a patient, and a healthy/unhealthy decision has to be made. However, the values of λ0 and λ1 are not known as they are in fact random. Specifically, each is assumed to be exponentially distributed, λ0 with mean value ˉ λ 0, and λ1 with mean value ˉ λ 1. With this model, the likelihood ratio is replaced by the Bayesian factor. The decision threshold is set to η= P0 P1 Cfa Cmd =1. M=10 observations are made on a patient, yielding the measured values y1,…yM. If ˉ λ 0=1 and ˉ λ 1= ˉ λ 0/4, which of the following represents the Bayesian decision rule (numbers are rounded):
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