In cases of immune system over activity, the body attacks and damages its own tissues (autoimmune diseases). Immune deficiency diseases decrease the body's ability to fight invaders, causing vulnerability to infections.
Standard deviation is a measure of spread (like Range, Variance, or IQR) so it tells you how wide or concentrated your data is. You can interpret it as how far away the typical/average observation is from the mean.
The standard deviation is kind of the mean of the mean, and often can help you find the story behind the data. To understand this concept, it can help to learn about what statisticians call normal distribution of data.he standard deviation is kind of the mean of the mean, and often can help you find the story behind the data. To understand this concept, it can help to learn about what statisticians call normal distribution of data.