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.
Want to avoid getting the flu? A good start is to know what causes it. This illness is different from a cold. While more than 100 different viruses can cause a cold, only influenza virus types A, B, and C cause the flu. Type A and B viruses cause the large seasonal outbreaks. Type C usually causes milder respiratory symptoms. While the flu vaccine can help protect you from types A and B, there is no immunization for type C virus. Type A flu viruses are also found in many different animals, including ducks, chickens, pigs, whales, horses, and seals.