Research done by the University of Edinborough in Scotland concludes that if the technological progression of extraterrestrials is similar to that of humans, then they are likely to have moved away from analog radio transmissions in favor of digital broadcasting.
Digital transmissions are much more difficult to detect. If extraterrestrials were broadcasting analog signals for a period of 100 years (like humans), but have switched to digital broadcasts, then the window for intercepting those signals still making their way through space is very narrow, according to Duncan Forgan, the leader of this study.
This study will be published in the upcoming edition of the International Journal of Astrobiology.
Based on Forgan’s calculations, “the probability of making contact is roughly one in 10 million.”