An Econometrics Lesson

From "An Econometrics Lesson":

When you look at data over time, it is important to ask yourself how many data points you really have. With a strong trend, you probably should just think of yourself as having two data points--the beginning and the end point. If there are a few sharp swings in the data, then you might have three or four effective data points. The fewer the number of effective data points, the harder it is to distinguish among alternative sources of causality.

That is why most macro-econometrics is junk science.

I may say, that is also why most macroeconomics (IS-LM, for example) is junk science.