Research has shown human beings to be notoriously bad decision makers in general. which type of psychologist was most likely to have carried out this type of research

The answer to this question is: Cognitive

Cognitive research publishes new empirical and theoretical work covering all areas of Cognition. Since the researchers want to examine how human's make a decision in general, they need to cover all aspects that could affect that decision, such as personality, wealth, situation, intelligence, etc.