What does "Average" mean?


What percentage of positive people will test positive according to your term "Average"? Your answer is greatly appreciated. Keep up the good work!!


Hi. Thank you for your question. A lot of people get confused regarding the definition of the word "average". The word "average" generally means what is found in the middle of a range of values, or what is common. In other words, generally speaking, it can be the 50th percentile (50%), the mid-point, intermediate, the mean, the norm, etc. etc. Statistically speaking, there are a number of different ways that statisticians can determine the average value of things (mean, median, mode, norm, etc.).

Not all people fall within the average. For example, when we say that the "average period of time from HIV infection, to the start of AIDS related symptoms, is approximately 10 years", this does NOT mean that everyone will start showing symptoms at 10 years. What it does mean is that approximately half of infected people will already be showing symptoms by 10 years after infection, and approximately half of infected people will take longer than 10 years before AIDS related symptoms begin.

When we say that the "average period of time to show positive on the antibody test is 25 days", this does NOT mean that everyone will be showing positive by 25 days. Some people will show positive by this point in time, and others will not.

When we are talking about an average value of anything (the average number of sexual partners among teenagers, the average life span of a person, etc.), there can be a lot of variability from person to person. Therefore, what may be an average value, may not apply to every member of that group. An average is merely a statistical tool to determine what is common, or mid-range within a group.

If you have any further questions, please feel free to call the Centers for Disease Control at 1.800.232.4636 (Nationwide).