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The effect on the correlation coefficient of discretizing data was investigated in two ways. First, the theoretical effect of dichotomizing data was calculated, and it was shown that the resulting correlation coefficient is considerably less than that between the underlying bivariate normally distributed variables. Second, computer simulations were performed of a model in which a continuous variable (measured with some error) gives rise to a counting variable through a mechanism in which the count is zero below a certain threshold value for the continuous variable and then increases linearly as the continuous variable increases. It was shown that the correlation coefficient between the observed values of the continuous and counting variables decreased as (a) the measurement error increased, (b) the slope of the relationship decreased, and (c) the number of counts decreased. It is concluded that caution is required when interpreting correlation coefficients when one or both of the variables consist of a few (say only four or five) discrete scores. 相似文献
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Growth factor responsiveness of human retinal pigment epithelial cells 总被引:21,自引:0,他引:21
K H Leschey S F Hackett J H Singer P A Campochiaro 《Investigative ophthalmology & visual science》1990,31(5):839-846
Growth factor effects on DNA synthesis in density-arrested human retinal pigment epithelial cells were assessed by [3H]-thymidine incorporation. Acidic and basic fibroblast growth factor and epidermal growth factor were potent stimulators, whereas platelet-derived growth factor, insulinlike growth factor-1, and insulin were weak or modest stimulators when used alone. When used in combination, each of the above growth factors caused a significant enhancement of [3H]-thymidine incorporation regardless of its effect when used alone. The combination of all four growth factors was significantly more effective than all other combinations, demonstrating synergism in their action. Similar results were found in cell proliferation assays. In contrast to this, transforming growth factor-beta inhibited the ability of each of the other growth factors and serum-containing media to stimulate [3H]-thymidine incorporation. These data suggest that DNA synthesis in human retinal pigment epithelial cells can be modulated by several growth factors, some in a stimulatory or synergistic manner and at least one in an inhibitory manner. A better understanding of these complex interactions may provide insights relevant to normal and abnormal ocular wound healing. 相似文献
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CA von Arnim R Spoelgen ID Peltan M Deng S Courchesne M Koker T Matsui H Kowa SF Lichtenthaler MC Irizarry BT Hyman 《The Journal of neuroscience》2006,26(39):9913-9922
The beta-amyloid (Abeta) precursor protein (APP) is cleaved sequentially by beta-site of APP-cleaving enzyme (BACE) and gamma-secretase to release the Abeta peptides that accumulate in plaques in Alzheimer's disease (AD). GGA1, a member of the Golgi-localized gamma-ear-containing ARF-binding (GGA) protein family, interacts with BACE and influences its subcellular distribution. We now report that overexpression of GGA1 in cells increased the APP C-terminal fragment resulting from beta-cleavage but surprisingly reduced Abeta. GGA1 confined APP to the Golgi, in which fluorescence resonance energy transfer analyses suggest that the proteins come into close proximity. GGA1 blunted only APP but not notch intracellular domain release. These results suggest that GGA1 prevented APP beta-cleavage products from becoming substrates for gamma-secretase. Direct binding of GGA1 to BACE was not required for these effects, but the integrity of the GAT (GGA1 and TOM) domain of GGA1 was. GGA1 may act as a specific spatial switch influencing APP trafficking and processing, so that APP-GGA1 interactions may have pathophysiological relevance in AD. 相似文献
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Psychological Disturbance and its Associations in the Children of the Gujarati Community 总被引:1,自引:1,他引:0
Latha Hackett Richard Hackett David C. Taylor 《Journal of child psychology and psychiatry, and allied disciplines》1991,32(5):851-856
The infrequent referral of Asian children to child psychiatry clinics was noted. By administering Rutter's scale A2 to samples of Gujarati and English parents with children between the ages of 4 and 7 years a lower rate of disturbance was demonstrated among the Asian sample providing an explanation for the original observation. Family and child-rearing factors associated with disturbance were identified. 相似文献
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The performance of the LCx HIV RNA Quantitative (LCx HIV), AMPLICOR HIV-1 MONITOR version 1.5 (MONITOR v1.5), and Quantiplex HIV-1 RNA version 3.0 (bDNA v3.0) viral load assays was evaluated with 39 viral isolates (3 A, 7 B, 6 C, 4 D, 8 E, 4 F, 1 G, 4 mosaic, and 2 group O). Quantitation across the assay dynamic ranges was assessed using serial fivefold dilutions of the viruses. In addition, sequences of gag-encoded p24 (gag p24), pol-encoded integrase, and env-encoded gp41 were analyzed to assign group and subtype and to assess nucleotide mismatches at primer and probe binding sites. For group M isolates, quantification was highly correlated among all three assays. In contrast, only the LCx HIV assay reliably quantified group O isolates. The bDNA v3.0 assay detected but consistently underquantified group O viruses, whereas the MONITOR v1.5 test failed to detect group O viruses. Analysis of target regions revealed fewer primer or probe mismatches in the LCx HIV assay than in the MONITOR v1.5 test. Consistent with the high level of nucleotide conservation is the ability of the LCx HIV assay to quantify efficiently human immunodeficiency virus type 1 group M and the genetically diverse group O. 相似文献
9.
应用放射配体结合法证实大鼠胸腺内存在降黑素特异结合部位,该结合位点可以满足特异结合部位的基本条件:1.低结合容量;2.高亲和力;3.可饱和性;4.可逆性;5.对降黑素高度特异性。此外,该特异结合位点具昼夜节律;亚细胞分布的研究表明以细胞核含量最高,线粒体次之,并具有年龄依赖性降低,以出生时最高。 相似文献
10.
A galE via (Vi antigen-negative) mutant of Salmonella typhi Ty2 retains virulence in humans. 总被引:5,自引:8,他引:5 下载免费PDF全文
D M Hone S R Attridge B Forrest R Morona D Daniels J T LaBrooy R C Bartholomeusz D J Shearman J Hackett 《Infection and immunity》1988,56(5):1326-1333
We have recently described the construction of a galE derivative of Salmonella typhi Ty2 (Ty2H1) which had a 0.4-kilobase deletion in the galE gene and was sensitive to galactose-induced lysis when cultured with greater than or equal to 0.06 mM galactose (D. M. Hone, R. Morona, S. Attridge, and J. Hackett, J. Infect. Dis. 156:167-174, 1987). We now report the selection of a rifampin-resistant, via derivative of Ty2H1, EX462. Compared with the Ty2 parent strain, EX462 was serum sensitive and highly attenuated in the mouse mucin virulence assay. When four human volunteers ingested 7 X 10(8) viable EX462, two became ill and developed a typhoidlike disease with fever and bacteremia. Blood isolates from these individuals were indistinguishable from the vaccine strain by a variety of criteria. We concluded that, even in a via background, the galE mutation was not attenuating for S. typhi in humans. 相似文献