00:01
So we've covered a variety of biases already,
let's get into the Hawthorne and Rosenthal
effects and they are combined to make something
resembling placebo effect, we will talk more
about placebo effect on the lecture about
experiments. So Hawthorne effect is also called
the observer effect and it is named after
a case in the Hawthorne factory, where they
discovered that when you turn the lights up
in the factory the workers tended to work
harder. In other words, individuals modify
their behavior when they are being watched,
that's the Hawthorne effect. So scientists
tend to recruit patients who have a better
adherence to drug therapies, who have a more
likelihood of staying in a study, therefore
less likelihood to have future loss to follow-up,
they are special individuals, they're more
likely to be good subjects. In other words,
they're going to respond in a positive way
more likely than other individuals not chosen
for a study. That's Hawthorne effect. That's
when these individuals are going to perform
simply because they are in a study. Sometimes
the inclusion exclusion criteria that we use
for randomized controlled trials will exclude
people who are ill in other ways not related
to our study. In other words, we are excluding
comorbidities, as a result, the end product
is a sample of individuals in a study who
are systematically healthier than those who
aren't in a study. It's a kind of healthy
worker effect almost. So again, the individuals
in our study are more likely to perform better,
because they're in the study. Now similar
to Hawthorne effect is the Rosenthal effect.
01:44
Sometimes it's called the Pygmalion effect
and sometimes it's called the self-fulfilling
prophecy. And the way it works is like this; simply
by interacting with subjects in a study they
may respond better to you, as a result of
your expectations. In other words, the researchers
expectations of a study subject will affect
how they respond. Consider this example, let's
say you go to a classroom and tell a teacher,
"You know that student over there? That student
is very bright and he might be very gifted
in the future, I want you to keep an eye on
that student." In truth the student isn't particularly
special, but the teacher thinks that he is,
as a result, the teacher spends a lot of time
with that student and actually creates the
conditions whereby that student succeeds.
In other words, bringing about the expectation,
fulfilling the prophecy, that's Rosenthal
effect. Similar to Rosenthal effect is the
Golem effect, it's actually a kind of Rosenthal
effect. That's when lowered expectations result
in lowered performance. Let's say the teacher
was told, "See that student over there, that
student is not very bright, don't expect a
lot from that individual" In fact the student
is perfect fine, perfectly bright, but the
teacher ignores the student, perhaps treats
him poorly and the student performs to a low
standard as a result. Again, self-fulfilling
prophecy, a Golem effect. Think about what
this means in the context of a randomized
controlled trial, anytime the researcher has
a relationship or contact with the study subjects,
they may be eliciting a response that is unnatural.
We try to minimize that kind of contact as
a result, or maybe even prevent the researcher
from knowing which individuals are getting
what kinds of treatment. In other words, the
Rosenthal and Hawthorne effects are the primary
reasons that we have blinding in randomized
controlled trials. Remember blinding is when
the researchers don't know which subjects
are getting therapies, and sometimes the subjects
don't know whether or not they are getting
the therapies either. We will talk more about
blinding when we talk about experiments in
another lecture.