Study limitations

There were missing valnes for some residence locations of the casualties and for some crash locations. These missing values were imputed using simple imputation from proportions estimated on observations without missing-values. The rates for PTW riders by gender, age gronp and location separately were not estimated we are concerned abont the reliability of the estimates because of the small number of PTW trips in the RTS. The mobility data provide information only about residents of the 

We were unfortunately not able to estimate confidence intervals of injury rates because of the multiplicity of the estimation steps estimates from a mobility survey (with a complex design), estimates of seasonality ratios from another survey (with complex design), estimates (connts) of those injured from the registry and ratios between estimates. 

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The characteristic function and the moment generating function are important tools for computing moments of distributions, studying limits of sequences of distributions, and finding the distribution of sums of independent variables. If Z — X + F, where X and T are independently distributed according to the distribution functions F(x) and 6( y) respectively, the distribution function of Z is given by... 

Chromosome aberrations were detected in lymphocytes of individuals acutely intoxicated by methyl parathion by the inhalation route (Van Bao et al. 1974). Blood samples were taken 3-6 days after exposure and again at 30 and 380 days. A temporary but significant (p<0.05) increase was noted in the frequency of stable chromosomal aberrations in the exposed individuals. The study limitations include small sample size, absence of a control group, lack of quantification of exposure levels, and a possible concomitant exposure to other substances via the dermal route. 

An adverse effect of lead on pregnancy rate has been noted in some animal studies (Kennedy et al. 1975). Acute-duration gavage administration of 390 mg lead/kg/day as lead acetate to rats resulted in a sharp decrease in pregnancy rates. This effect was not noted at 39 mg lead/kg/day. The study limitations include a lack of measurement of blood lead levels and lack of statistical analysis of pregnancy incidence. A decrease in the number of implantations was noted in untreated female mice that were mated to males that had been treated with 141 mg/kg/day lead chloride in the drinking water for 3 months... 

Comparative Toxicokinetics. The absorption, distribution, metabolism, and excretion of acrylonitrile in rats has been studied. Limited work in other species suggests that important species differences do exist. Further evaluation of these differences, and comparison of metabolic patterns in humans with those of animals would assist in determining the most appropriate animal species for evaluating the hazard and risk of human exposure to acrylonitrile. 

From a consideration of data provided in studies limited to the metathesis of 2-pentene, several views of the stereochemistry have been recently advanced. For the most part, they deal only with steric influences caused by alkyl groups coming from the reacting olefin. 

Reminiscent of the trend with laboratory studies, most (33 out of 43 cited above) uncontrolled clinical trials with either healthy volunteers or cardiovascular patients suggest that oral and intravenous NO donors at therapeutic doses acutely inhibit platelet activation in vivo (vide supra). Aside from their lack of long-term dosing and a placebo control group, several considerations restrict the predictive clinical value of these uncontrolled clinical studies limited numbers of subjects nonuniform criteria for subject entry and treatment outside of the trial induction of adrenaline or... 

Intact muscle/meat is studied Limited sample size... 

Ion-Activity Products. As in the determination of the amount sorbed through Equation 2, the characterization of surface precipitates often utilizes measurements made solely on the aqueous solution phase. Solubility studies limited in this way run a risk of being ambiguous as to mechanism because of the lack of direct information about the solid phase (10). In respect to the aqueous solution phase, ambiguity can be minimized if equilibrium is approached both from supersaturation and from undersaturation if the equilibration time is varied... 

Selection bias Occurs when there is a systematic difference between the characteristics of the people selected for a study, or who agree to participate, and the characteristics of those who are not selected, or who do not agree to participate (e.g., in a study limited to volunteers). 

Although a number of epidemiological studies have reported an increased risk of lung cancer among occupationally exposed beryllium workers, deficiencies in the studies limit any unequivocal conclusion. Specific criticisms concern the lack of consideration of latent effects, of smoking history, and of exposure to other potential carcinogens and the underestimation of expected lung cancer deaths in comparison populations. "... 

The absence of data at planting for parameters to be measured in the study limits comparisons to current conditions in the plantation. 

As discussed in Section 2.4, there is some evidence that nickel may affect the release of prolactin from the pituitary. In a study limited by decreased water and food intake and increased temperatures, oral exposure of rats resulted in increased pituitary weights in male but not female rats (RTI 1986, 1988a, 1988b). However, decreased prolactin levels were observed in female rats treated with nickel chloride in the drinking water throughout the breeding and lactation of two litters (Smith et al. 1993). 

In summary, these results portrayed an intermediate situation where the PT is coupled to the Sn2 geometry change and charge shifting features. It should now be apparent that a study limited to the RC and the TS and lacking a reaction path analysis would have missed most ofthe important mechanistic features discussed herein. 

Clinical studies in patients with sleep disorders have shown that oral melatonin supplementation may alter sleep architecture. Subjective improvements in sleep quality and improvements in sleep onset and sleep duration have been reported. However, the significance of these findings is impaired by many study limitations. 

Information on toxic effects of acute-duration exposure to PBBs by routes other than oral are limited to data on hepatic, renal, dermal, and ocular effects of inhalation and dermal exposure in rats or rabbits (Millischer et al. 1980 Needham et al. 1982 Norris et al. 1975a Waritz et al. 1977), but these data may not be reliable due to study limitations and possible delayed lethality. Quantitative data for inhalation and dermal absorption of PBBs are lacking. Studies of inhalation and dermal absorption following exposure to soil containing PBBs (i.e., bioavailability studies) would be useful for assessing risk at a hazardous waste... 

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