For example, you might say unemployment is the number of adults who do not have full time jobs. Or you could say unemployment is the number of adults between the age of 25 and 65 who do not have jobs. Or you could say unemployment is the number of employable adults between the age of 25 and 65 who do not have full time jobs. OR.... or ... or...
Exactly, and this is why we have different measures. We can use the measure that best fits what we are trying to define.
Or alternately we can do like Special EdBaiamonte and use whatever one we think will score points in a political argument instead of what is logical.
True. However trying to make logic out of unemployment is not an easy task. This is mostly because the act of being un-employed is itself illogical. One starts to make excuses / explanations for why someone is unemployed and then extrapolate that because of this or that excuse there must be millions like that person. For example, went back to school, is working under the table, is under employed, is "discouraged," is laid off, is a homemaker now, ...
The assumptions we make for "why" people are unemployed, lead to assumptions on what unemployment means. But they are just assumptions.
High unemployment might be a good thing when pay goes through the roof and more people switch back to being homemakers, or go back to school... Or it might be a bad thing when more people are claiming dependency and collecting welfare. Or it also might be a bad thing if the people who are unemployed don't meet the needs of the employers and are unwilling to re-train or create their own jobs, thus become dead beats or homeless.