All along in this course I have been
teaching you terminology and techniques,
but what I have really been doing is
giving you tools. Now we start the part
of the course in which you will learn to
use these tools in specific ways. No
longer is the task to use the hammer of
sum of x divided by n to pound a central
tendency nail. Now you will use all of
your statistical tools, follow hypothesis
testing instructions, and build a real
statistical analysis. I'm going to teach
you about hypothesis testing. So that
means that we develop a hypothesis and
we test it, right? What makes this part of
statistics difficult is when we decide
what hypothesis to test. Many students
are surprised to learn that we do not
begin with a hypothesis that we would like, to prove but rather, we begin with a
hypothesis that nothing happened. We're
going to posit two explanations, two
hypotheses for our research, the first
the hypothesis we actually test, is the
null hypothesis, which says that no
differences exist; there was no effect.
The best explanation is chance, and here
is why we begin with the null hypothesis
and we don't begin with the hypothesis
that we would like to prove. It's ancient
aliens guy from The History Channel!
Ancient aliens guy is an internet meme
about a guy on a television show about
aliens. No matter what the topic is, his
explanation is always aliens. He can find
evidence for aliens wherever he looks.
Fundamentally the problem with his
approach is that he begins with the
alternative hypothesis, not the null
hypothesis. He begins with his
explanation that everything unknown,
unknowable, or misunderstood can be
explained by aliens. If scientists,
historians, researchers are still
searching for answers, he steps into that
gap
with his explanation. Aliens did it!
Starting with an alternative hypothesis
leads us astray in so many ways,
conflating possibility with probability.
I mean can you prove that aliens didn't
build the Egyptian pyramids and
Stonehenge? If you can't prove it didn't
happen then how can you say aliens
didn't do it, I mean anything is possible!
The answer is we're not trying to prove
anything. We're looking for the most
likely explanation with the fewest
assumptions, the most parsimonious
explanation. I can't prove that you were
not miraculously transported home last
night by supernatural means, but most
likely you drove home. Overvaluing
certainty, ancient aliens guy would
really really believe that aliens make
crop circles and abduct Texans. He might
say that "You scientists are always
talking about probability and likelihood,
but you can never be certain about
anything like I am!" Well my answer to
that is that certainty is overrated, and
usually a refuge for people who don't
actually have evidence. Lots of people
claim to be certain that they know what
happens to us Homo sapiens after we die,
but as a critical thinker you should
never accept the certainty of someone
who could not possibly know what they
claim to be so certain about. All
ignorance is equal. The argument from
ignorance leaves no way to judge whether
other hypotheses are correct or not. If
all that is required is a gap in
knowledge, an opening of ignorance, a
question that science is still figuring
out, then any crackpot supernatural
extraterrestrial explanation is just as
good as any other. Once you abandon
evidence as your standard for belief,
there's no way to choose between
competing theories and non-falsifiability. When scientists show how
Easter Island was really constructed,
that doesn't undermine ancient alien
guy's alien hypothesis, just because he
was wrong about Easter Island doesn't
mean the aliens didn't kill the
dinosaurs, or castrate the heaven's gate
cult guys, or leave behind their crystal
skulls. His alien hypothesis can never be
proven false no matter how many times he is proven wrong. True believers and
conspiracy theorists start with the
conclusion, and then look for evidence to
support it. They ignore the evidence that
does not support their predetermined
conclusion, but not only is that not
honest, it's not necessary. Only if you
want to believe in aliens are aliens a
plausible explanation. Aliens are not
required. It works without that
assumption and we can do better. So let's
do some science.
