[Sundae]

Oh for goodness sake.
Aliens can only abduct you if you have certain chemicals in your bloodstream. They use tracking devices and people with the relevant chemicals show up like beacons. Specifically anyone on anti-psychotic or psychotrophic drugs. This has been found to be the case in over 60% of abductions.

It's difficult to specify because of course the aliens have now infiltrated the drugs industry, and occasional and subtle changes have been made to many medications so that people show up on alien scanners.

Depending on metabolism, alcohol can sometimes show up as a marker. This accounts for approx 30% of abductions. Teetotallers are less often taken (less than 5%, with the other 5% classified as "other"), but any number of products now have hidden alcohol in them, including many low budget foods. It also serves as an addictive ingredient, making people buy more when they don't even like the taste, just like alcoholics.

Some people however are able to "tip-over" i.e. drink so much that they saturate the alien's screen and make their exact location difficult to pin point. This is what is assumed to have happened in cases where people who have no drugs in their system have been abducted. Given that we only have the word of these people regarding what they hae ingested however, it is impossible to be 100% sure.

Wearing a hat is unlikely to help anyone, and the statistics which suggest it does are meaningless - everyone knows that statistics can be manipulated to show anything you like.