Researcher: A number of studies have suggested that, on average, clients in short-term psychotherapy show similar levels of improvement regardless of the kind of psychotherapy they receive. So any client improvement in short-term psychotherapy must be the result of some aspect or aspects of therapy that are common to all psychotherapies -- for example, the presence of someone who listens and gives attention to the client. Which one of the following, if true, would most weaken the researcher's argument? ['The studies found that psychotherapy by a trained counselor does not result in any greater improvement, on average, among clients than does simple counseling by an untrained layperson.', 'On average, clients improve more dramatically when they receive long-term psychotherapy, a year or longer in duration, than when clients receive short-term psychotherapy.', 'More-experienced therapists tend to use a wider range of techniques and interventions in psychotherapy than do inexperienced therapists.', 'The methods by which the studies measured whether clients improved primarily concerned immediate symptom relief and failed to address other important kinds of improvement.']