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Book 1. 20220808. Section 3.3.4.

Open Rajon010 opened this issue 2 years ago • 3 comments

That equality does not hold. Consider the univariate standard normal distribution and N=4. Suppose the sample is {-1, -1, 1, 1}. Then the joint probability density equals N(1 | mean=0, var=1) ^ 4. The probability density for the sample mean (-1 + -1 + 1 + 1) / 4 = 0 is N(0 | mean=0, var=0.25). Grab a calculator https://www.danielsoper.com/statcalc/calculator.aspx?id=54, we have that N(1 | mean=0, var=1) ^ 4 is about 0.24 ^ 4 and N(0 | mean=0, var=0.25) is about 0.79. Obviously, they differ. Intuitively, the probability of a sample mean collects the probability of all possible samples having this sample mean value, and should be larger than the probability of any single such sample. 0

Rajon010 avatar Aug 13 '22 07:08 Rajon010

Same issue in section 4.6.4.2.

Rajon010 avatar Sep 02 '22 11:09 Rajon010

Also, that N should be an exponent rather than a numerator. 圖片

Rajon010 avatar Sep 02 '22 11:09 Rajon010

Missing period. 圖片

Rajon010 avatar Sep 02 '22 11:09 Rajon010

Re 3.65. I meant to write proportional to, not equality. See https://github.com/probml/pml-book/issues/512

murphyk avatar Apr 17 '23 03:04 murphyk

All fixed, thanks.

murphyk avatar Apr 17 '23 03:04 murphyk