Non-randomized trials can introduce bias because treatments are assigned to groups without randomization.

“a non-randomized trial uh sometimes gets referred to as an open label trial where you take two groups of people and you give one of them a treatment and you give the other one either a placebo or a different treatment but you don't randomize them there's a reason that they're in that group”

“a non-randomized trial uh sometimes gets referred to as an open label trial where you take two groups of people and you give one of them a treatment and you give the other one uh either a placebo or a different treatment but you don't randomize them there's a reason that they're in that group so you might say um you know we want to study the effect of a certain antibiotic on a person that comes in the ER and we're going to take all the people that come in who look a certain way maybe they have a certain a fever of a certain level or a white blood cell count of a certain level and we're going to give them the antibiotic and the people who come in but they don't have those exact signs or symptoms we're going to not give an antibiotic to and we're going to follow them that's kind of a lame example you could do the same sort of thing with surgical interventions we're going to try to ask the question is surgery better than antibiotics for appendicitis or suspected appendicitis but we don't randomize the people to the choice there's some other factor that is going to determine whether or not we do that and as you can see that's going to have a lot of limitations because presumably there's a reason you're making that decision and that reason will undoubtedly introduce bias”