Bioinformatics, Vol 14, 772-782, Copyright © 1998 by Oxford University Press
R Karchin and R Hughey
MOTIVATION: Hidden Markov models can efficiently and automatically build
statistical representations of related sequences. Unfortunately, training
sets are frequently biased toward one subgroup of sequences, leading to an
insufficiently general model. This work evaluates sequence weighting
methods based on the maximum-discrimination idea. RESULTS: One good method
scales sequence weights by an exponential that ranges between 0.1 for the
best scoring sequence and 1.0 for the worst. Experiments with a curated
data set show that while training with one or two sequences performed worse
than single-sequence Probabilistic Smith-Waterman, training with five or
ten sequences reduced errors by 20% and 51%, respectively. This new version
of the SAM HMM suite outperforms HMMer (17% reduction over PSW for 10
training sequences), Meta-MEME (28% reduction), and unweighted SAM (31%
reduction). AVAILABILITY: A WWW server, as well as information on obtaining
the Sequence Alignment and Modeling (SAM) software suite and additional
data from this work, can be found at http://www.cse.ucse.
edu/research/compbio/sam.html
ARTICLES
Weighting hidden Markov models for maximum discrimination
Department of Computer Engineering, Jack Baskin School of Engineering, University of California, Santa Cruz, CA 95064, USA. rph@cse.ucsc.edu
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