I would take a different view and ask: How many credible UFO sightings have there been?

According to thestacker.com/stories/1095/states-most-ufo-sightings, "Since its founding in 1974, the National UFO Reporting Center (NUFORC) has documented around 90,000 UFO sightings, with almost 95% of those sightings supposedly easily explained away as military tests, weather balloons, or other terrestrial activity." If correct, that makes at least 4,500 sightings that cannot be easily dismissed.

The National UFO Reporting Center, btw, has a weekly list of sightings going back to 2006 at http://www.nuforc.org/webreports/ndxpost.html.

In any case, if only a half of those 4,500 reportings are true UFOs sightings, it means there are several thousand civilizations in the universe very much more advanced in intelligence and technology than humanity. And how many more species are as intelligent as us or somewhat less so?

As such, it seems to me that it's highly likely that there are many life forms in the universe which are very intelligent.