Suppose that on January 1 1999, the government creates a million new jobs. Only those currently without work may apply. The new jobs attract 3 million applicants, half of whom would not otherwise be looking for work in January. Does official unemployment go up or down? By how much?

The new jobs create an increase in employment of 1 million. But, according to the definition of unemployment, it creates an additional 1.5 million people looking for work and therefore classified as part of the labor force. So the effect of the new jobs is to increase employment by 1 million and increase the labor force by 1.5 million. 
So does unemployment rise or fall? Let x be the size of the labor force without the new progarm, and let y be the number of people who would have jobs without the new program. Then, without the program, the unemployment rate is
     u = 1 - y/x.
Now, with the program, the number of people with jobs goes up to y+1, while the size of the labor force goes up to x+1.5. That is, the unemployment rate with the program is
     v = 1 - (y+1)/(x+1.5).
The change in the unemployment rate caused by the new program is therefore
     v - u = 1-(y+1)/(x+1.5) - (1-y/x).
You can easily work out that this expression is positive if y > 2x/3, and negative otherwise. Note that if y > 2x/3, then u = 1-y/x < 1/3 That is, if the original unemployment rate is less than 33.3 percent, the program increases unemployment.