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Sample A: Cover Page of Thesis, Project, or Dissertation Proposal

Sample A: Cover Page of Thesis, Project, or Dissertation Proposal

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obustness in the predicted expression differences between two given tissue states [69]. These<br />

tissue states can be disease conditions, time points in a response curve, drug <strong>or</strong> toxin treatment<br />

groups, etc. Generating such a subset <strong>of</strong> genes, generally several dozen to several hundred in a<br />

list, falls within a type <strong>of</strong> classical statistical issue now well-understood f<strong>or</strong> Microarray data.<br />

That is, any such data set has a large feature (N) to sample (P) bias, where N >> P, in the initial<br />

measurement set [70]. In fact, this characteristic violates most statistical analysis method’s<br />

assumptions about the data [70]. A common test is the identification <strong>of</strong> unexpressed genes and<br />

genes whose expression does not change, such that these genes can be excluded [70, 71]. From<br />

here, investigat<strong>or</strong>s typically employ additional metrics to facilitate further down selection <strong>of</strong> the<br />

data’s features, by identifying those genes with the largest fold-change, noise-to-signal ratio, <strong>or</strong><br />

some other dimensionality reduction rule in <strong>or</strong>der to identify significant changes [52, 69-73].<br />

A great deal <strong>of</strong> eff<strong>or</strong>t has been extended to refine these identification methods, either in the<br />

alg<strong>or</strong>ithms themselves <strong>or</strong> in the statistical power, by expl<strong>or</strong>ing false discovering rates, etc [57, 74,<br />

75]. A maj<strong>or</strong> presumption about these approaches is that a significant change <strong>of</strong> any gene’s<br />

expression levels is found by identifying a large change, whether absolute <strong>or</strong> as a ratio, compared<br />

to a starting level. This does not match what is known about the expression <strong>of</strong> particular classes<br />

<strong>of</strong> genes, such as those regulating transcription, where very small changes may lead to large<br />

effects on other genes [76]. A similar assumption is that the biological tolerance <strong>of</strong> steady state<br />

variance is the same f<strong>or</strong> all genes [67]. The steady state reflects an average <strong>of</strong> the sample<br />

mixtures, but tolerance <strong>of</strong> expression variation will be different f<strong>or</strong> different genes in different<br />

cell types, and in samples having different components [58].<br />

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