5,076 reputation
1424
bio website quantdec.com
location Northeastern US
age 14
visits member for 4 years, 3 months
seen 2 days ago

Consultant (environmental and spatial stats a specialty), expert witness, and teacher. I can be reached through (outdated but still valid) links posted on my web site.

Twitter: @WilliamAHuber // ASA-P website: http://amstatphilly.org/


Why waste time learning, when ignorance is instantaneous?

--T(iger) Hobbes.

For any complex problem there is a simple solution. And it's always wrong.

--[Mis?]attributed to H.L. Mencken by Dava Sobel, Longitude.


Jul
3
answered Combinatorics: Mean and Variance of an indicator function of items arranged in a circle.
Jul
1
comment How to understand Demartines theorem
This is a minor variant of the Central Limit Theorem, which asserts the standardized version of $||X||_2^2$ is asymptotically Normal. It requires that $X$ have finite variance.
Jun
26
comment Transforming vector elements to element indices
Because matrix operations represent linear transformations and the relationship between Y and X is not linear, no such Q exists.
Jun
18
comment Does affine equivariance implies shape unbiasedness?
Some things to consider: when $\sigma(X)=0$ (the $p\times p$ zero matrix) the procedure is trivially equivariant but obviously not unbiased. More generally, when $\sigma$ is equivariant unbiased and $p\gt 1$, the procedure $\tau(X)=\lambda\sigma(X)$ is also equivariant but when $\lambda^p\ne \lambda$ it must be biased. This suggests that dividing $\sigma(X)$ by its determinant might not be the right definition of "unbiased" to be using.
Apr
7
comment Holder's inequality
Your second statement is not well defined until you assume both $X$ and $Y$ are strictly positive.
Mar
7
reviewed Approve suggested edit on another question on surds and how to use math symbols in this site
Feb
26
comment Lower bound for non-negative definite matrix
The matrix $$\left( \begin{array}{cc} 0 & 1 \\ -1 & 2 \\ \end{array} \right)$$ is non-negative definite but your expression equals $-2$. Perhaps you would like to stipulate that $A$ also be symmetric?
Feb
16
awarded  Good Answer
Jan
16
awarded  Custodian
Jan
16
reviewed Leave Open How do you find the angle between a diagonal of a cube and one of its faces?
Jan
16
reviewed Looks OK How do you find the angle between a diagonal of a cube and one of its faces?
Jan
16
reviewed Looks OK Integration Techniques - Adding [arbitrary] values to the numerator.
Jan
16
reviewed Approve suggested edit on Card game question
Dec
16
comment Determine the number of revolutions the normal to a curve makes as it moves along a curve in three dimensions?
That is correct, which is why I claimed your question is not well-defined! It only becomes so once you fix a pair of points on the sphere once and for all.
Dec
6
comment If $X$ is independent of $Z$ and $Y$ is dependent with $Z$ is it possible for $X + Y$ to be independent of $Z$?
@Did Thank you for pointing that out!
Dec
6
comment If $X$ is independent of $Z$ and $Y$ is dependent with $Z$ is it possible for $X + Y$ to be independent of $Z$?
If $X+Y$ is independent of $Z$ and $X$ is independent of $Z$, then $(X+Y)-X = Y$ must also be independent of $Z$.
Dec
6
comment Determine the number of revolutions the normal to a curve makes as it moves along a curve in three dimensions?
You can make this question well-defined by first restricting to curves whose normals are never zero, allowing you to define a unit normal everywhere, and assuming this unit normal is a continuous map into the unit sphere. Select two points on the unit sphere not in the image of that map. Use (say) a stereographic projection based at one of them to project the curve into the plane. Define the number of "revolutions" to be the winding number of the (projected) unit normal around the second point.
Dec
6
comment Mapping CDF's to each other
The result is false for discrete distributions. A simple example is given by two Bernoulli variables with parameters $p$ and $p'$ such that $p\ne p'$ and $p\ne 1-p'$.
Oct
25
comment How do you calculate an upper-confidence bound on a problem with 2 means?
That's right--and leave out the left endpoint of the interval altogether.
Oct
25
comment How do you calculate an upper-confidence bound on a problem with 2 means?
This is a nice exposition but it addresses a slightly different problem: the question asks for a UCL of the mean, not a symmetric CI for the mean.