In response to an unknown trigger, the immune system may begin producing antibodies that instead of fighting infections, attack the body's own tissues. Treatment for autoimmune diseases generally focuses on reducing immune system activity.
What's taught in school. Some of the items in standardized achievement tests measure the knowledge or skills that students learn in school. In certain subject areas, such as mathematics, children learn in school most of what they know about a subject.
A standard deviation is a statistic that is calculated as the square root of a variance, or a data set calculated by taking the mean of the squared differences between each value and the mean value. Because the differences are squared, units of variance are not units of data.