Drake Equation

So Aliens are real. If you don't believe that I don't know what to tell you. So my concern is just how many alien races are there out there? I believe there have got to be thousands that have been in contact with humans or that at least go whipping by our little planet on a regular bases. 

  In the 1960's a radio astronomer named Frank Drake came up with a equation that involves factors, such as the fraction of stars that develop planets, then multiplying all the following factors.

Rate of star birth...  50 new stars in the milky way every year.

50% of new stars develop planets...  0.4% of these planets are habitable.

90% of habitable planets develop life...  90% of these habitable planets will bear only simple life.

Leaving 10% of habitable planets to contain intelligent life...  90% of this intelligent life will never talk to the stars.

10% of intelligent life develops interstellar communications...  Some of these civilizations will die before ever making contact though.

Life span of civilizations on average, last 10,000 years... 

With this theory your left with....

900 civilizations possible alive today in our galaxy being able to contact us.