object orie’d data analysis, last time distance weighted discrimination: revisit microarray data...

Object Orie’d Data Analysis, Last Time

Distance Weighted Discrimination:

• Revisit microarray data

• Face Data

• Outcomes Data

• Simulation Comparison

22

UNC, Stat & OR

Twiddle ratios of subtypes

33

UNC, Stat & OR

Why not adjust by means?

DWD robust against non-

proportional subtypes…

Mathematical Statistical Question:

Are there mathematics behind this?

(will answer next time…)

Distance Weighted Discrim’n Maximal Data Piling

HDLSS Discrim’n Simulations

Main idea:

Comparison of

• SVM (Support Vector Machine)

• DWD (Distance Weighted Discrimination)

• MD (Mean Difference, a.k.a. Centroid)

Linear versions, across dimensions

HDLSS Discrim’n SimulationsConclusions:

• Everything (sensible) is best sometimes• DWD often very near best• MD weak beyond Gaussian

Caution about simulations (and examples):• Very easy to cherry pick best ones• Good practice in Machine Learning

– “Ignore method proposed, but read paper for useful comparison of

others”

HDLSS Discrim’n Simulations

Can we say more about:

All methods come together

in very high dimensions???

Mathematical Statistical Question:

Mathematics behind this???

(will answer now)

HDLSS Asymptotics

Modern Mathematical Statistics: Based on asymptotic analysis I.e. Uses limiting operations Almost always Occasional misconceptions: Indicates behavior for large samples Thus only makes sense for “large” samples Models phenomenon of “increasing data” So other flavors are useless???

nlim

HDLSS Asymptotics

Modern Mathematical Statistics: Based on asymptotic analysis Real Reasons:Approximation provides insightsCan find simple underlying structureIn complex situations

Thus various flavors are fine:

Even desirable! (find additional insights)

0,lim,lim,lim,lim dndn

HDLSS Asymptotics: Simple Paradoxes

For dim’al Standard Normal dist’n:

Euclidean Distance to Origin (as ):

d

d

dd

d

IN

Z

Z

Z ,0~1

)1(pOdZ


As ,

-Data lie roughly on surface of sphere,

with radius

- Yet origin is point of highest density???

- Paradox resolved by:

density w. r. t. Lebesgue Measure

d

)1(pOdZ

d



indep. of

Euclidean Dist. Between and

(as ):

Distance tends to non-random constant:

d

d

dd INZ ,0~2

)1(221 pOdZZ

1Z

1Z 2Z


Distance tends to non-random constant:

•Factor , since

Can extend to Where do they all go???

(we can only perceive 3 dim’ns)

)1(221 pOdZZ

nZZ ,...,

1

222

121 XsdXsdXXsd 2



indep. of

High dim’al Angles (as ):

- Everything is orthogonal???

- Where do they all go???

(again our perceptual limitations)

- Again 1st order structure is non-random

d

d

dd INZ ,0~2

)(90, 2/121

dOZZAngle p

1Z

HDLSS Asy’s: Geometrical Represent’n

Assume , let

Study Subspace Generated by Data

Hyperplane through 0,

of dimension

Points are “nearly equidistant to 0”,

& dist

Within plane, can

“rotate towards Unit Simplex”

All Gaussian data sets are:

“near Unit Simplex Vertices”!!!

“Randomness” appears

only in rotation of simplex

n

d ddn INZZ ,0~,...,1

d

d

Hall, Marron & Neeman (2005)

HDLSS Asy’s: Geometrical Represent’n

Assume , let

Study Hyperplane Generated by Data

dimensional hyperplane

Points are pairwise equidistant, dist

Points lie at vertices of:

“regular hedron”

Again “randomness in data” is only in rotation

Surprisingly rigid structure in data?

1n

d ddn INZZ ,0~,...,1

d2

d~

n

HDLSS Asy’s: Geometrical Represen’tion

Simulation View: study “rigidity after rotation”

• Simple 3 point data sets

• In dimensions d = 2, 20, 200, 20000

• Generate hyperplane of dimension 2

• Rotate that to plane of screen

• Rotate within plane, to make “comparable”

• Repeat 10 times, use different colors


Simulation View: shows “rigidity after rotation”


Explanation of Observed (Simulation) Behavior:

“everything similar for very high d ”

• 2 popn’s are 2 simplices (i.e. regular n-hedrons)

• All are same distance from the other class

• i.e. everything is a support vector

• i.e. all sensible directions show “data piling”

• so “sensible methods are all nearly the same”

• Including 1 - NN


Straightforward Generalizations:

non-Gaussian data: only need moments

non-independent: use “mixing conditions”

Mild Eigenvalue condition on Theoretical Cov. (Ahn, Marron, Muller & Chi, 2007)

All based on simple “Laws of Large Numbers”

2nd Paper on HDLSS Asymptotics

Ahn, Marron, Muller & Chi (2007) Assume 2nd Moments

Assume no eigenvalues too large in sense:

For assume i.e.

(min possible)

(much weaker than previous mixing conditions…)

d

jj

d

jj

d1

2

2

1

)(1 do 1 d


Background:

In classical multivariate analysis, the statistic

Is called the “epsilon statistic”

And is used to test “sphericity” of dist’n,

i.e. “are all cov’nce eigenvalues the same?”

d

jj

d

jj

d1

2

2

1


Can show: epsilon statistic:

Satisfies:

• For spherical Normal,

• Single extreme eigenvalue gives

• So assumption is very mild

• Much weaker than mixing conditions

d

jj

d

jj

d1

2

2

1

1,1d

1 d

1

d

1


Ahn, Marron, Muller & Chi (2007) Assume 2nd Moments

Assume no eigenvalues too large, :

Then

Not so strong as before:

1 d

dOXX pji )1(

)1(221 pOdZZ


Can we improve on:

?

John Kent example: Normal scale mixture

Won’t get:

ddddiININX *10,05.0,05.0~

dOXX pji )1(

)1(pjiOdCXX


Notes on Kent’s Normal Scale Mixture

• Data Vectors are indep’dent of each other

• But entries of each have strong depend’ce

• However, can show entries have cov = 0!

• Recall statistical folklore:

Covariance = 0 Independence

ddddiININX *10,05.0,05.0~

0 Covariance is not independence

Simple Example:

• Random Variables and

• Make both Gaussian

• With strong dependence

• Yet 0 covariance

Given , define

YX

1,0~, NYX

0c

cXX

cXXY


Simple Example:


Simple Example, c to make cov(X,Y) = 0


Simple Example:

• Distribution is degenerate

• Supported on diagonal lines

• Not abs. cont. w.r.t. 2-d Lebesgue meas.

• For small , have

• For large , have

• By continuity, with

0,cov YXc

c

c 0,cov YX

0,cov YX


Result:

• Joint distribution of and :

– Has Gaussian marginals

– Has

– Yet strong dependence of and

– Thus not multivariate Gaussian

Shows Multivariate Gaussian means more

than Gaussian Marginals

YX

0,cov YX

X Y


Further Consequences of Geometric Represen’tion

1. Inefficiency of DWD for uneven sample size(motivates weighted version, Xingye Qiao)

2. DWD more stable than SVM(based on deeper limiting distributions)

(reflects intuitive idea feeling sampling variation)(something like mean vs. median)

3. 1-NN rule inefficiency is quantified.

HDLSS Math. Stat. of PCA, I

Consistency & Strong Inconsistency:

Spike Covariance Model, Paul (2007)

For Eigenvalues:

1st Eigenvector:

How good are empirical versions,

as estimates?

1,,1, ,,2,1 dddd d

1u

1,,1 ˆ,ˆ,,ˆ uddd

HDLSS Math. Stat. of PCA, II

Consistency (big enough spike):

For ,

Strong Inconsistency (spike not big enough):

For ,

1

0ˆ, 11 uuAngle

1

011 90ˆ, uuAngle

HDLSS Math. Stat. of PCA, III

Consistency of eigenvalues?

Eigenvalues Inconsistent

But known distribution

Unless as well

nn

dL

d

2

,1,1̂

n

HDLSS Work in Progress, I

Batch Adjustment: Xuxin Liu

Recall Intuition from above:

Key is sizes of biological subtypes

Differing ratio trips up mean

But DWD more robust

Mathematics behind this?

Liu: Twiddle ratios of subtypes

HDLSS Data Combo Mathematics

Xuxin Liu Dissertation Results:

Simple Unbalanced Cluster Model

Growing at rate as

Answers depend on

Visualization of setting….

d d


Asymptotic Results (as ):

For , DWD Consistent

Angle(DWD,Truth)

For , DWD Strongly Inconsistent

Angle(DWD,Truth)

d

2

1

2

1

0

090


Asymptotic Results (as ):

For , PAM Inconsistent

Angle(PAM,Truth)

For , PAM Strongly Inconsistent

Angle(PAM,Truth)

d

2

1

2

1

0 rC

090


Value of , for sample size ratio :

, only when

Otherwise for , PAM Inconsistent

Verifies intuitive idea in strong way

rC

22

1cos

2

1

r

rCr

0rC

r

1r

1r

The Future of Geometrical Repres’tion?

HDLSS version of “optimality” results?

•“Contiguity” approach? Params depend on d?

•Rates of Convergence?

•Improvements of DWD?

(e.g. other functions of distance than inverse)

It is still early days …

State of HDLSS Research?

DevelopmentOf Methods

MathematicalAssessment

…

(thanks to:defiant.corban.edu/gtipton/net-fun/iceberg.html)

object orie’d data analysis, last time distance weighted discrimination: revisit microarray data...

Documents

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simple paradoxesas

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