Specific refractive index increments of polyisoprenes with high cis-1,4 content have been determined in six solvents at 20� and λ 546 nm. A linear relationship was found between the refractive index increment dn/dc = n and the refractive index of the solvent nl : N45620 = 1.687 - 1.105n1 The results are compared with the best values reported for natural rubber which are usually employed for polyisoprene in light scattering measurements.

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Negative affectivity (NA) has been shown to be strongly and consistently correlated to patient reported, subjective health indicators. Therefore, subjective health indicators may or may not give an accurate assessment of the individual's true health status. NA can be expected to act as a general nuisance factor in health research, one that taps organically spurious variance. The pervasive influence of NA may confound the results and complicate the interpretation of health related quality of life instruments, such as the SF‐36. OBJECTIVE: The purpose of this study was to evaluate the potential influence of NA on the MOS SF‐36. METHODS: We used Structural Equation Modeling (SEM) techniques to evaluate the SF‐36 and the impact of NA on the Mental and Physical Components in a sample taken from the 1990 National Survey of Functional Health Status (NHS). RESULTS: The percent of shared variance of the Physical Health and Mental Health indicators and the Physical and Mental Health factors combined are physical function (.0603), role physical (.0817), bodily pain (.0720), health perception (.0600), role emotional (.0486), vitality (.0756), general mental health (.5207) and social function (.0811). General mental health (GMH) indicators are virtually identical to NA indicators. The percent of shared variance of the NA/GMH factor and Physical Health and Mental Health is .4422 and .9781 respectively. CONCLUSIONS: The present results suggest that about 47 percent of Physical Health and 98 percent of Mental Health is due to the influence of NA/GMH. This may account for the lack of discriminative ability, shown in previous studies, of the Mental Health factor and Mental Component Scale Score.

Health‐related quality of life (HRQoL) research suggests that, due to unique characteristics of a disease state, disease specific tools are better discriminators of health status than generic tools. OBJECTIVE: To compare generic (SF‐12) versus disease specific (SIBDQ) quality of life tools in a cohort of patients receiving treatment for Crohn's Disease (CD). METHODS: Structural Equation Modeling techniques were used to evaluate the effectiveness of the SF‐12 and the SIBDQ for evaluating health status patients with CD. A cohort of 151 patients with CD receiving drug therapy was administered both instruments via telephone survey. RESULTS: The variance explained by the SIBDQ in this population was 11.6% while the SF‐12 explained 55.7%. Adapted models of both the SIBDQ and SF‐12 resulted in explained variance of 54.8% and 84.1%, respectively. CONCLUSIONS: Given these results, the generic HRQoL tool was significantly better than the disease specific tool at measuring and accounting for health status in this population. Patients with moderate or severe CD have previously been shown to have differing clinical response to therapy based upon disease severity, whereby patients with more severe disease have better response. Due to these possible unique clinical outcomes of newer medications such as infliximab, the effectiveness of disease specific tools may be compromised since improving therapies may affect HRQoL in a different manner than therapies previously available. Other innovative therapies, such as biologic response modifiers for rheumatoid arthritis, may have similar findings related to HRQoL measurement. This potential problem with HRQoL measurement is likely to increase as biopharmaceutical and pharmacogenomic research increases the number and rate of new product approvals. These findings have important implications related to measurement of HRQoL in clinical trials and pharmacoeconomic evaluation of medications. This suggests a need for careful reevaluation of disease specific tools given the clinical effects of newer therapies.