How much of a stat is actually lowered when it's lowered 'one stage'?

Question

How much of the stat is actually lowered, in terms of real numbers? When they say, for example:
"EMPOLEON's speed was lowered harshly!"

It has Speed lowered 2 stages, how much is each of those stages?

Answer 1

This question explains it: http://pokemondb.net/pokebase/1400/how-much-do-stat-raising-moves-power-them-up

The second stages is x2, so "lowered harshly" means the speed would be halved the first time the move is used.

Answer 2

Http://i54.tinypic.com/nvqww5.png <= Screenshot of the part explaining the stages.

Source: http://www.psypokes.com/lab/stats.php