What is the average age for a 4 year old?

Answer 1

If you take a random sample of kids who are 4 and you record their ages with accuracy (to the nearest day or some reasonable fraction of a year), I think the average age would turn out to be very close to 4.5 years. You would hit a wide range of ages from 4 years and zero days all the way to 4 years and 364 days. The true average might not be exactly 4.5 years; it may depend on things like differing mortality rates at one end of the year or the other. Age is one of those things that you can record and use as a discrete variable or as a continuous variable. It is in fact continuous. If you are studying a narrow age range, particularly of children, thinking of age as continuous is probably useful. Things can change so quickly for children. On the other hand, if you are looking at age in the context of a national census, then knowing that John Doe is 61.7 years old and that Jane Doe is 2.1 years old might be more detail than you need given your purpose. For example, would anyone think that people who are 61.7 years old will compare with Jane's group significantly differently from people who are 61.8 years old? In fact in that case you may even make things easier by grouping individuals into categories with ranges of 5 or 10 years without losing the meaning of your comparisons. It depends on your hypothesis, the degree of detail that you expect to find in your analysis, and on what successful or unsuccessful techniques others have used.