The standard deviation is a measure of how the data is clustered about the mean. For large sets of data, approximately 68.3% of the data lies within one standard deviation of the mean and approximately 95.4% of the data lies within two standard deviations of the mean.
Influenza (also known as the flu) is a contagious respiratory illness caused by influenza viruses. It can cause mild to severe illness, and at times can lead to death. The best way to prevent the flu is by getting a flu vaccination each year.
The flu is caused by influenza virus types A, B, and C. Both type A and type B flu viruses are responsible for the seasonal outbreaks of flu. Type A flu viruses are found in many different animals, including ducks, chickens, pigs, and horses.