The rate of a given outcome for participants with a particular characteristic divided by the rate of that outcome for participants without the characteristic. See Case-comparison design, Epidemiologcal studies, Epidemiology, Hazard ratio, Odds ratio
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Raphe nuclei
Nuclei arrayed around the midline of the brain stem (‘raphe’ referring to a ridge separating two symmetrical parts of a body). Forming part of the reticular system, the nuclei are evident at most levels of the brain stem (from the midbrain to the spinal cord and forebrain). Their main role involves the manufacture and synthesis of …
Ras
An intracellular tyrosine kinase (an enzyme) originally discovered through its role in oncogenesis, now found to be involved in a variety of developmental pathways. See Boss (or bride of seven less), Developmental genetics, Enzyme, Sevenless, R7 and R8 photoreceptors, Tyrosine kinase receptor/pathway
Random effects
Coefficientsvarying in value that are modeled as the variance in outcomes due tounexplained differences between higher-level sampling units, between groups orclasses. These may include deviations in intercepts or slopes: differencesbetween the overall average outcome and the group average; or differencesbetween the average slope and the group slope. The deviations by group are saidto be random …
Radian
An SI unit of angle in which one radian encloses an arc equal to the radius of a concentric circle. It is a way of measuring angles (see figure below for further explanation). One radian = 57.295 angle in which one radian encloses an arc equal to the radius of a concentric circle. See …
Radical behaviorism (or environmentalism)
The most extreme form of behaviourism developed by John B. Watson (1878-1958) in which he claimed that classical conditioning contained both the necessary and sufficient conditions for development to occur. He became so extreme in his views on development partly as a consequence of his clashes with those he saw as maturationists. See Behaviorism, Necessary …
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Radial palmar grasp
Grasping with the part of the hand closest to the thumb (i.e., the radial palm), but including use of the thumb and index finger. See Grasp response, Palmar grasp, Pincer grasp (or grip)
Race-ethnicity
A set of categories used to distinguish subgroups of a larger society. The categories used have varied over time and in different societies. In the US, categories used for the 2000 Census refer to both race (based on physical characteristics) and ethnicity (based on cultural characteristics such as common language or religious tradition). The Census …
Radial glial cells
Also referred to as the Bergmann fibers of the Golgi epithelium cells, they are a special class of astrocytes that extend from the ventricles to the cortex and along which migrating neurons travel to their final destinations. With the completion of migration, the radial glia fibers break apart and the cells are transformed into fibrous astrocytes. Some …
R7 and R8 photoreceptors
Blue and ultraviolet sensitive classes of photoreceptors in the Drosophila fruit fly compound eye. The eye consists of about 800 units (viz., ommatidia) that in turn are composed of eight neural photoreceptor cells together with twelve non-neural supporting cells (viz., bristle, cone and pigment). R8 is considered to be the ‘founder’ cell that specifies the other photoreceptor …