Transcript What, Exactly, is the Food Propensity Questionnaire?

Bayesian Methods for Density and
Regression Deconvolution
Raymond J. Carroll
Texas A&M University and University of
Technology Sydney
http://stat.tamu.edu/~carroll
Co-Authors
 Bani Mallick
Abhra Sarkar 
 John Staudenmayer
Debdeep Pati 
Longtime Collaborators in
Deconvolution
Peter Hall
Aurore Delaigle
Len Stefanski
Overview
• My main application interest is in nutrition
• Nutritional intake is necessarily multivariate
• Smart nutritionists have recognized that in
cancers, it is the patterns of nutrition that
matter, not single causes such as saturated fat
• To affect public health practice, nutritionists
have developed scores that characterize how
well one eats
• Healthy Eating Index, Dash score,
Mediterranean score, etc.
Overview
• One day of French fries/Chips will not kill you
• It is your long-term average pattern that is
important
• In population public health science, long term
averages cannot be measured
• The best you can get is some version of selfreport, e.g., multiple 24 hour recalls
• This fact has been the driver behind much of
measurement error modeling, especially
including density deconvolution
Overview
•
Analysis is complicated by the fact that on a
given day, people will not consume certain
foods, e.g., whole grains, legumes, etc.
• My long term goal has been to develop methods
that take into account measurement error, the
multivariate nature of nutrition, and excess
zeros.
Why it Matters
•
What % of kids U.S. have alarmingly bad diets?
• Ignore measurement error, 28%
• Account for it, 8%
• What are the relative rates of colon cancer for
those with a HEI score of 70 versus those with
40?
• Ignore measurement error, decrease 10%
• Account for it, decrease 35%
Overview
• We have perfectly serviceable and practical
methods that involve transformations, random
effects, latent variables and measurement errors
• The methods are widely and internationally used
in nutritional surveillance and nutritional
epidemiology
• For the multivariate case, computation is
“Bayesian”
• Eventually though, anything random is
assumed to be Gaussian
• Can we not do better?
Background
• In the classical measurement error –
deconvolution problem, there is a variable, X,
that is not observable
• Instead, a proxy for it, W, is observed
• In the density problem, the goal is to estimate
the density of X using only observations on W
• Also, in population science contexts, the
distribution of X given covariates Z is also
important (very small literature on this)
Background
• In the regression problem, there is a response Y
• One goal is to estimate E(Y | X)
• Another goal is to estimate the distribution
of
Y given X, because variances are not always
nuisance parameters
Background
• In the classic problem, W = X + U, with U
independent on X.
• Deconvoluting kernel methods that result in
consistent estimation of the density of X were
discovered in 1988 (Stefanski, Hall, Fan and  )
• They are kernel density estimates with kernel
function
K decon (x)
Background
• In the classic problem, W = X + U, with U
independent of X.
• The deconvoluting kernel is a corrected score
for a ordinary kernel density function, with the
property that for a bandwidth h,
E  K decon (W-x 0 )/h|X  =K (X-x 0 )/h
• Lots of results on rates of convergence, etc.
Background
• There is an R package called decon
• However, a paper to appear by A. Delaigle
discusses problems with the package’s
bandwidth selectors
• Her web site has Matlab code for cases that the
measurement error is independent of X,
including bandwidth selection
Problem Considered Here
• Here is a general class of models. Here are W
and X
Wij =X i +U ij (X i )
E U ij (X i ) | X i   0
var U ij (X i ) | X i    u2 (X i )
• The W’s are independent given X
Background
• There is a substantial econometric literature
on technical conditions for identification in many
different contexts (S. Schennach, X. Chen, Y.
Hu)
• The problem I have stated is known to be
nonparametrically identified if there are 3
replicates (and certain technical completeness
assumptions hold)
Problem Considered Here
• Here is a general class of models, First, Y
Yi =g(X i )+ε i (X i )
E ε i (X i ) | X i   0
var ε i (X i ) | X i    (X i )
2
ε
• The classical heteroscedastic model where the
•
variance is important
Identified if there are 2 replicate W’s
Background
• The econometric literature invariably uses sieves
with orthogonal basis functions
• The theory follows X. Shen’s 1997 paper
Background
• In practice, as with non-penalized splines, 5-7
basis functions are used to represent all
densities and functions
• Constraints (such as being positive and
integrating to 1 for densities) are often ignored
• In the problem I eventually want to solve, the
dimension of the two densities = 19 (latent stuff
all around
• Maybe use multivariate Hermite series?
Problem Considered Here
• There is no deconvoluting kernel method that
does density or regression deconvolution in the
context that the distribution of the measurement
error depends on X
Problem Considered Here
• It seems to me that there are two ways to
handle this problem in general
• Sieves  be an econometrician
• Bayesian with flexible models
• Our methodology is explicitly Bayesian, but
borrows basis function ideas from the sieve
approach
Model Formulation
• We borrow from Hu and Schennach’s example
and also Staudenmayer, Ruppert and
Buonaccorsi
Wij = X i
1/2
u
+ s (X i )U ij
1/2
ε
Yi = g(X i )+ s (X i )ε i
• Here, U is assumed independent of X
• Also, e is independent of X
Model Formulation
• Our model is
Wij = X i
+ s1/2
u (X i )U ij
Yi = g(X i )+ s1/2
ε (X i )ε i
• Like previous authors, we model
s ε (X i ) and s u (X i )
as B-splines with positive coefficients
• We model g(Xi ) as B-spline
•
As frequentists, we could model the densities of
X, U, and e by sieves, and appeal to Hu and
Schennach for theory
• We have not investigated this
Model Formulation
• Our model is
Wij = X i
+ s1/2
u (X i )U ij
Yi = g(X i )+ s1/2
ε (X i )ε i
• As Bayesians, we have modeled the densities of
X, U, and e by DPMM
• We have found that mixtures of normals, with
an unknown number of components, is much
faster, just as effective, and very stable
numerically
Model Formulation
• We found that by fixing the number of
components to a largish number works best
• The method concentrates on a lower number of
components (Rousseau and Mengersen found
this in a non-measurement error context)
• There are lots of issues involved: (a) starting
values; (b) hyper-parameters; (c) MH
candidates; (d) constraints (e.g., zero means),
(e) data standardization, etc.
Model Formulation
• Here is a simulation example of density
deconvolution and homoscedasticity with a
mixture of normals for X and a Laplace for U
• The settings come from a paper not by us
• There are 3 replicates, so the density of U is also
estimated by our method (we let DKDE know
the truth)
• I ran our R code as is, with no fine tuning
Model Formulation
Model Formulation
• Here is another example
• Y = sodium intake as measured by a food
frequency questionnaire (known to be biased)
• W = same thing, but measured by a 24 hour
recall (known to be almost unbiased)
• We have R code for this
Model Formulation
The dashed
line is the
Y=X line,
indicating the
bias of the
FFQ
Multivariate Deconvolution
• There are also multivariate problems of density
deconvolution
• We have found 4 papers about this
• 3 deconvoluting kernel papers, all assume the
density of the measurement errors is known
• 1 of those papers has a bandwidth selector
• Bovy et al (2011, AoAS) model X as a mixture of
normals, and assume U is independent of X and
Gaussian with known covariance matrix. They
use an EM algorithm.
Multivariate Deconvolution
• We have generalized our 1-dimension
deconvolution approach as
Wijk = X ij
+ s1/2
uj (X ij )U ijk
• Again, X is a mixture of multivariate normals, as
is U
• However, standard multivariate inverse Wishart
computations fail miserably
Multivariate Deconvolution
• We have generalized our 1-dimension
deconvolution approach as
Wijk = X ij
+ s1/2
uj (X ij )U ijk
• We use a factor analytic representation of the
component specific covariance matrices with
sparsity inducing shrinkage priors on the factor
loading matrices (A. Bhattacharya and D.
Dunson)
• This is crucial in flexibly lowering the dimension
of the covariance matrices
Multivariate Deconvolution
Multivariate inverse
Wisharts on top, Latent
factor model on bottom
Blue = MIW, green =
MLFA.
Variables are (a) carbs;
(b) fiber; (c) protein and
(d) potassium
Conclusion
• I still want to get to my problem of multiple
nutrients/foods, excess zeros and measurement
error
• Dimension reduction and flexible models seem a
practical way to go
• Final point: for health risk estimation and
nutritional surveillance, only a 1-dimensional
summary is needed, hence better rates of
convergence