Background frequencies

With the scores scaled in bit units, the relative entropy of the target and background frequencies is computed as... 

When the defining set is small, there is an inadequate representation of the range of allowed positional variation in terms of either amino acid frequencies or types. Pseudo counts have been used for estimates of such unobserved data (Brown et al., 1993 Lawrence et al., 1993 Claverie, 1994 Tatusov et al., 1994 Henikoff and Henikoff, 1996 Sjo-lander et al., 1996). Such pseudo counts have been based on background frequencies, existing substitution matrices (Henikoff and Henikoff, 1992), and Dirichlet priors (Brown et al., 1993 Tatusov et al., 1994 Sjolander et al., 1996). Tatusov et al. (1994) reported that the Dirichlet priors (Brown et al., 1993 Sjolander et al., 1996) were most effective in... 

Consider the of the clinical event frequency related to drug versus the background frequency of... 

In particular, high-dose data usually cannot identify a threshold. A threshold is a dose or exposure below which there is no effect. It is often assumed that there is no threshold for an end point, like a gene mutation, that may involve one molecule of the toxicant and one target molecule in such a case, the dose-response relationship would be linear at low doses. If the observed relationship is linear over the dose range studied and if the fitted line is extrapolated to no effect (or the background frequency of effects) at zero dose, linear kinetics with no threshold are likely. But data are usually not clear. Even such a large carcinogenesis study as the EDqi study conducted by... 

Pietra et al. (1990) studied the effects of some antidepressants on the volume-induced reflex contractions of the rat urinary bladder. The urinary bladder of anesthetized rats was filled via the recording catheter by incremental volumes of warmed saline until bladder contractions occurred as a result of central activity. Volume-induced contractions were then recorded and occurred rhythmically and reproducibly for 2-3 h. Drug activity was assessed in each animal against the background frequency of bladder contractions, for a 15-min time period following intravenous administration of different doses. 

The proportion of female Sprague-Dawley rats developing mammary tumors decreases very rapidly as the dose decreases (American Biogenics Corporation, 1986 McCormick, 1988 Thakur, 1991, 1992). The observed dose-response relationship is sublinear. Furthermore, the biological mechanism by which atrazine and simazine cause this response is most likely a threshold mechanism thus, the sublinear dose-response relationship contains a range of positive doses for which the frequency of the response is not increased above the background frequency at zero dose (Andersen et al., 1998 Connor et al., 1998 Eldridge et al 1998 Simpkins et al, 1998). 

Calculation of a frequency (or rate) of the number of reports per 1000 patients, prescriptions, DDD/ lOOOp / day or another available denominator. From there several external comparisons can be made with similar frequencies based on number of cases in an unexposed population, also coined as baseline risk or background frequency, or the number of cases in a population exposed to another medicine from the same therapeutic category. This approach is only possible when reliable denominator data are present. Moreover the head-to-head comparisons require limited under-, over- or selective reporting in the two frequencies of observed possible induced drug problems. 

Check that in Expected frequency calibration, Predefined background frequencies is selected (see Notes 17 and 18), that the Background model is set to upstream-noorf, and that the selected Organism is the one for which the sequences were retrieved (see Note 19). 

Predefined background frequencies. Compare oligonucleotide frequencies observed in the query sequence to those of a reference sequence (the background model). 

The introduction of 20 mph zones in London has reduced the frequency of injury accidents within the zones by about 42% and reduced the frequency of accidents involving fatal or serious injury KSI by about 53%. Both of these reductions allow for the background frequency of injury accidents declining over the period. 

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