1) 80 patients were randomly assigned to four groups.
2) 80 patients were randomised to four groups.
If the usage is okay, which one is better? 1 or 2?
What was 'randomised' was the overall trial, not the participants. The collocation 'randomised trial' is very strong. These two -
are way out in front of alternatives in BNC. With a total of 48, they account for nearly half of BNC's hits for 'randomised + <any noun>. Also prominent are 'randomised study/-ies', which come respectively 3rd and 5th. Adding these two, the total would come to 68 - comfortably more than half.1 RANDOMISED TRIALS 27
2 RANDOMISED TRIAL 21
The preference is even clearer in COCA:
b1 RANDOMIZED TRIALS 75
2 RANDOMIZED TRIAL 72
3 RANDOMISED TRIALS 49
4 RANDOMISED TRIAL 35
Off-topic, but ...
It took me rather a long time to get the best out of of COCA/BNC, but now I cannot imagine working without it/them. I have been disabused of a few mistaken beliefs, and heartened by the confirmation of a few 'feelings'. If many members are grateful to UsingEnglish.com, I think all of us owe a debt of gratitude to Mark Davies.