11 research outputs found
RAPTT: An Exact Two-Sample Test in High Dimensions Using Random Projections
In high dimensions, the classical Hotelling's test tends to have low
power or becomes undefined due to singularity of the sample covariance matrix.
In this paper, this problem is overcome by projecting the data matrix onto
lower dimensional subspaces through multiplication by random matrices. We
propose RAPTT (RAndom Projection T-Test), an exact test for equality of means
of two normal populations based on projected lower dimensional data. RAPTT does
not require any constraints on the dimension of the data or the sample size. A
simulation study indicates that in high dimensions the power of this test is
often greater than that of competing tests. The advantage of RAPTT is
illustrated on high-dimensional gene expression data involving the
discrimination of tumor and normal colon tissues
AR(1) sequence with random coefficients: Regenerative properties and its application
Let be a sequence of real valued random variables such that
, where
are i.i.d. and independent of initial value
(possibly random) . In this paper it is shown that, under some natural
conditions on the distribution of , the sequence
is regenerative in the sense that it could be broken up into
i.i.d. components. Further, when and are independent, we
construct a non-parametric strongly consistent estimator of the characteristic
functions of and
Apparent ice accumulation rate in East Antarctica: Relation with temperature and thinning pattern
We present here formal evidence of a strong linkage between temperature and
East Antarctic ice accumulation over the past eight hundred kiloyears, after
accounting for thinning. The conclusions are based on statistical analysis of a
proposed empirical model based on ice core data from multiple locations with
ground topography ranging from local peaks to local valleys. The method permits
adjustment of the apparent accumulation rate for a very general thinning
process of ice sheet over the ages, is robust to any misspecification of the
age scale, and does not require delineation of the accumulation rate from
thinning. Records show 5% to 8% increase in the accumulation rate for every
1C rise in temperature. This is consistent with the theoretical
expectation on the average rate of increase in moisture absorption capacity of
the atmosphere with rise in temperature, as inferred from the
Clausius-Clapeyron equation. This finding reinforces indications of the
resilience of the Antarctic Ice Sheet to the effects of warming induced by
climate change, which have been documented in other studies based on recent
data. Analysis of the thinning pattern of ice revealed an exponential rate of
thinning over several glacial cycles and eventual attainment of a saturation
level