A therapist has created a new psychotherapy approach and initiates this treatment with a client. The therapist conducts a case study and publishes the results. Which factor is MOST likely to be present in this study?

A) Observer bias
B) Placebo effect
C) Lack of informed consent
D) High external validity

Observer Bias

A bias that occurs when an observer's expectations or preconceptions influence their perception and interpretation of events or data.

Placebo Effect

A phenomenon wherein a patient experiences a perceived improvement in condition due to believing they are receiving treatment, when in fact they have been given a non-active substance or intervention.

Informed Consent

A legal and ethical requirement ensuring individuals are fully aware of and understand the potential risks and benefits before agreeing to undergo a medical procedure or participate in a research study.