China
Africa
Explore chapters and articles related to this topic
M
Published in Filomena Pereira-Maxwell, Medical Statistics, 2018
As opposed to a unimodal distribution, a multimodal distribution is characterised by having two or more peaks, which often reflects the presence in a study sample of individuals from distinct populations with regard to the feature or variable in question. See also bimodal distribution, mode.
Some Statistical Procedures for Biomarker Measurements Subject to Instrumental Limitations
Published in Albert Vexler, Alan D. Hutson, Xiwei Chen, Statistical Testing Strategies in the Health Sciences, 2017
Albert Vexler, Alan D. Hutson, Xiwei Chen
Consider the problem of the estimation of the distribution function, FU, of a random variable U when observations from this distribution are contaminated by measurement error, that is, based on observations of random variables Y = U + ε, where ε represents measurement error. The estimation of FU has been referred to as deconvolution, since the distribution of each Yi is the convolution of the distributions of Ui and δi. Cordy and Thomas (1997) investigated the deconvolution of density by modeling the unknown distribution FU as a mixture of a finite number of known distributions. The mixture model was shown to be able to approximate a wide range of distributions. The authors also demonstrated that this approach can be applied to estimation of a unimodal distribution. In both models, parameters were estimated and large sample confidence intervals were constructed based on the well-known likelihood theory. Based on simulation studies, the good performance of the estimators and the confidence interval procedures were confirmed. The authors illustrated their methods by an application of data from a dietary survey reported by Clayton (1992), where the ratio of polyunsaturated to saturated fat intake (P/S) was measured for 336 males in a 1-week full-weighted dietary survey, and the authors considered the measured values of P/S for the ith individual as normally distributed with mean equal to the true value, UM, of P/S and constant measurement error variance.
Assessing variability of aerosols generated from e-Cigarettes
Published in Inhalation Toxicology, 2022
Darpan Das, Sarah-Marie Alam El Din, Jairus Pulczinski, Jana N. Mihalic, Rui Chen, Joseph Bressler, Ana M. Rule, Gurumurthy Ramachandran
The number size distributions measured by SMPS and APS together (Figure 3) indicate a unimodal distribution of particles with a mode size of ∼300 nm, irrespective of the e-liquid used. However, several studies have reported a bimodal distribution, with the modes reported at 200 nm and 1 µm (Zhao et al. 2018). The unimodal distribution in our study can be primarily attributed to the evaporation and aging of particles, causing the bimodal distribution to become unimodal as the aerosol ages (Schripp et al. 2013). In the present study, the SMPS and APS measurements were obtained after the aerosol had aged and the concentration had reached steady state (i.e. ∼50 min after the start of the experiment). Further, the dilution air provided (1:1 ratio of e-cig aerosol to dilution air) may have facilitated the quenching of the aerosol leading to quicker evaporation.
Modeling with a large class of unimodal multivariate distributions
Published in Journal of Applied Statistics, 2018
The representation of Khintchine [21] is given by Y =XZ, where X is uniform on Z, independent of X, has any distribution. Then Y has a unimodal distribution with mode at 0. Also, according to Khintchine [21], any unimodal density can be written as Y =XZ. To see this let us consider the situation of g is used to represent the density function of Z. To see more clearly the unimodality at 0, let us use the transform y=0, and is non-increasing for y>0.
Pharmaceutical suspensions of ursodeoxycholic acid for pediatric patients: in vitro and in vivo studies
Published in Pharmaceutical Development and Technology, 2021
Oriana Boscolo, Leandro Salvo, Cecilia Dobrecky, Eliana N. Fissore, Fabian Buontempo, Valeria Tripodi, Silvia E. Lucangioli
UDCA liquid suspensions, SA and SB, were developed to balance pediatric patients’ acceptability while improving UDCA bioavailability. Suspensions were in vivo and in vitro characterized. One suspension was designed with minimal number of excipients (SA) and the other one with the use of two suspending agents (SB), which improved slightly the rheological behavior and importantly the chemical stability, while presented better palatability. Both suspensions showed adequate physical, chemical and microbiological stability. They showed a unimodal distribution of particle size, which translated to a homogeneous distribution. Thus, the correct dose is guaranteed when being administered to pediatric patients. Both suspensions, SA and SB, can be stored at room temperature and in the fridge for at least 120 days and at 40 °C for 90 and 120 days, respectively. SA showed a higher variability in UDCA content compared to SB. The formulated suspensions met the USP specifications for dissolution test as well as related substances contents. Moreover, the developed suspensions met the content uniformity test and the criteria established by the USP and the European Pharmacopoeia. The UDCA presented a similar relative oral bioavailability when administered through the SA or the SB forms, without significant differences. It was demonstrated that when UDCA is loaded in suspensions like SA and SB, its oral bioavailability was noticeably higher than when a UDCA containing commercial tablet is crushed and dispersed in water to facilitate the oral administration to children. Finally, this work permitted to find suitable vehicles to allow accurate and convenient dose measurement while prevented UDCA during suspensions shelf life from degradation.