I think most of your numbers are reasonable, except the following:<br><br>% of life developing on habitable planet: 100%<br>There are thermodynamic arguments suggesting that life is inevitable once the conditions are right. Being in the habitable zone is a sufficient condition.<br><br>% of intelligent life capable of building civilisations: 0.00000001%<br>We have multiple intelligent species on earth, including  dolphins, crows, chimps, elephants and more. All of them have exhibited crude tool use, and all of them seem capable of communicating with each other to some degree. However, no lineage other than the great apes have the dexterity to build sophisticated tools, or been capable of the degree of sophisticated communication that seems necessary for a corpus of durable knowledge that spans generations. The fact that this only happened once in earth's history, and even then is a characteristic only of a single ancestral line, suggests to me that it's very unlikely. My estimate above is frankly optimistic.<br><br>% of communication ability developing: 100%<br>Assuming a species has the dexterity to build sophisticated tools, and the ability to communicate with each other to the degree necessary to build an intergenerational body of knowledge, it seems inevitable that they would build technology that produces detectable signals.<br><br>Length of time these signals would be detectable: optimistically, 200 years. This is not the lifetime of the civilisation, but the lifetime of their communication tech being detectable remotely. We already phased out broadcast tech after less than 100 years of radio broadcasting. 5G uses phased arrays for targeted communication, communication with objects in space uses focused laser beams, and the near-term quantum communication protocols would make any signal almost indistinguishable from noise. The window of time for detecting these signals is minute, unless a civilisation intentionally broadcasts.<br><br>I don't think your estimate for the number of civilisations per planet is sensible either. Thousands of great ape civilisations have developed on earth alone.<br><br>If I use 1,000 for this number, then I get an estimate of ~1.2e-005. Pessimistically, I get 1.2e-008.