Have you seen these pie charts that compare skilled, unskilled, and professional jobs over several decades? Usually, pie charts for the years 1950, 1991, and 2000 are shown. When only two charts are shown, it is usually 1950 and 1997, with the 1997 chart being identical to the 2000 chart.
This is unsubstantiated data that does NOT need to be shared.
It is important when you quote an original source, that you go to the original source and verify it. This data NEVER came from the Bureau of Labor Statistics as is usually indicated. The problem is that the US Government never uses these three categories to categorize occupations.
The source is usually listed as the "Bureau of Labor Statistics." (But it did not come from them.)
Sometimes the source is identified as coming from the "National Summit on 21st (Twenty-First) Century Skills for 21st (Twenty-First) Century Jobs" also known as the "21st Century Skills for 21st Century Jobs Summit", held on January 12, 1999, lead by Al Gore.
It is my understanding that someone prior to 1999 made up these statistics to make a point, and unfortunately, this unsubstantiated data has been quoted ever since.
As late as 2005, even the US Department of Education has been quoting these charts. That is the year that I stopped using these charts. I had used them so much in previous years that people at my presentations asked why I was not using them any more.
Note: Even as late as December 2010 I saw these charts used in a presentation.