Baseline variables associated with

The following example illustrates several issues and problems associated with the interpretation of p-values arising out of the t-tests. The setting is a very common one where a variable is measured at baseline and then subsequently at the end of the treatment period and the analysis focuses on the relative effects of the two treatments. 

Computer packages such as SAS can fit these models, provide estimates of the values of the b coefficients together with standard errors, and give p-values associated with the hypothesis tests of interest. These hypotheses will be exactly as Hqj, Hq2 and Hq3 in Section 6.3. Methods of stepwise regression are also available for the identification of a subset of the baseline variables/factors that are predictive of outcome. 

Although the average weekly dose of warfarin is between 30 and 40 mg, some patient-related variables are associated with a lower than usual dose advanced age (>65 years), elevated baseline INR, poor nutritional status, liver disease, hyperthyroidism, and concurrent use of medications known to enhance the effect of warfarin (Table 19-12). Prior to initiating therapy, the clinician should screen for the presence of contraindications to anticoagulation therapy and risk factors for... 

In this review we concentrate on individual-based studies. In case-control studies, subjects with already existing disease are retrospectively compared with control persons with respect to previous exposure. In cohort studies, individual exposure is measured at baseline and the cohort is followed over time for newly diagnosed outcome variables. Both case-control and cohort studies estimate the (relative) risk associated with exposure. Intervention studies utilize an experimental design and are mostly double blind trials with a defined treatment or placebo assigned randomly. Results from intervention studies, followed by cohort studies, make the greatest contributions to obtaining evidence of a causal relationship. Case-control studies are liable to particular bias, which give their results less credibility. 

Although these factors are similar to those described in Chapter 4, there are some relevant differences. In PCA (and hence in PCR), the factors explain most of the variance in the X regardless of whether such variance is or is not related to the analyte, whereas in PLS they explain not only variance in the spectral variables but also the variance of the property of interest. An example might be a series of graphite furnace measurements where a baseline shift appears owing to some variation in the temperature of the furnace because of a drift in the power supply. The variance associated with the baseline shift will generate a factor that should not be considered to predict the concentration of the analyte. 

The variable controlled during the expiratory phase is known as the baseline variable, most commonly, pressure, typically expressed as EPAP or PEEP. It is necessary to have a positive baseline pressure in bi-level devices to assure CO2 washout. Bi-level devices have also been shown to be effective in managing upper airway collapse, in patients with obstructive sleep apnea and overlap (14). Einally, a positive baseline pressure has been shown to decrease the work of breathing associated with intrinsic PEEP and improve... 

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