Standard Deviation (Volatility) Introduction. Standard deviation is a statistical term that measures the amount of variability or dispersion around an average. Standard deviation is also a measure of volatility. Generally speaking, dispersion is the difference between the actual value and the average value. The larger this dispersion or variability is, the higher the standard deviation. The smaller this dispersion or variability is, the lower the standard deviation.
MRI image showing a typical meningioma tumor. A meningioma is a tumor that arises from a layer of tissue (the meninges) that covers the brain and spine. Meningiomas grow on the surface of the brain (or spinal cord), and therefore push the brain away rather than growing from within it. Most are considered âbenignâ because they are slow-growing with low potential to spread. Meningioma tumors can become quite large. Diameters of 2 inches (5 cm.) are not uncommon.
Meningiomas may cause seizures, headaches, and focal neurological defects, such as arm or leg weakness, or vision loss. Patients often have subtle symptoms for a long period before the meningioma is diagnosed. Sometimes memory loss, carelessness, and unsteadiness are the only symptoms. Diagnosis is made by a contrast enhanced CT (computerized tomography) and/or MRI (magnetic resonance imaging) scan.