And once we have every search question or hypothesis,
then we make the manipulation of the independent variable.
And we measure our dependent variable.
That's the empirical study of the actual experiment.
We get the results of that, the dependent variable.
We do a data analysts to tell us whether or not there's a meaning
dependent variable difference due to the independent variable.
And then we actually interpret those findings.
And then the conclusions we reach are fed back Into the literature so
that other people can benefit by the fact that we'd done an experiment and
expand their knowledge about the topic that we're interested in.
So the rationale is the first thing we're going to talk about.
How do we determine what a hypothesis actually is.
And as I mentioned we can do that in many ways.
The hypothesis, which is some relationship between the dependent variable and
the independent variable can be counted through observation, through the research
literature, or through a theory that we have about how the dependent variable and
the independent variable are supposed to relate to each other.
So let's first talk about observation.
And I want to use a demonstration of that
from one of my favorite series of experiments
by Vincent Dethier at Princeton who is actually a behavioral biologist.
And he was interested in studying the housefly.
He said he studied houseflies because when you have that as your subject, houseflies,
you don't have the animal rights people telling you what you can do and can't do.
In fact, when people come to your office,
you have to keep them from doing away with your subjects by swatting them.
So nobody really worries about flies, but
they're very interesting creatures according to Dethier.
And he just was observing the flies,
he noticed something very interesting about them.
He noticed that when they were eating,
they walk around on their food before they eat.
That's not what we do, but it's what houseflies do.
You can always tell when a fly is eating or drinking because it has that proboscis,
when it's not eating or drinking, it's rolled up into the head.
But when it is eating or drinking it's rolled out as you can see here, and
actually you can know when the independent variable is taking place,
the fly is feeding.
So he said, why do they walk around on their food before they eat?
That is an observation.
Why can't I come over with an hypothesis based on that observation.
Well, maybe houseflies actually taste with their feet.
Not like us who have taste buds in our mouth and
on our tongue that tell us when something is what we want to eat.
And actually, it allows us to spit it out if it's something we don't want to eat.
Well, maybe the reason the housefly walks around on
the food before it eats is it actually has taste buds located on their feet.
That was his hypothesis.
Now how do you test that?
Well, first he jut actually hooked a little housefly to a rod so
he could move the housefly away.
And he said what I'll do is I'll change where the feed are,
relative to where the head is.
If I give the fly just plain water, and it's hungry, it won't drink or eat.
because it's not thirsty, it's hungry.
If I give the fly sugar water and it's hungry, it will eat.
So maybe I'll put the head over sugar water and the feed over plain water, and
if the taste is determined by the head like it is in most organisms,
then of course the fly will eat.
But if I put the head over plain water in the feed over sugar water,
then the fly, if it uses its feet to taste,
then the fact that its feet is over the sugar water, then it should eat.
So here's my manipulation, where the head is relative to where the feet is
to tell me whether or not the taste is located in the feet, or in the head.
That was his experiment, and this is what he did.
He put the fly down so its feet was in plain water, and
the head was over the sugar water, which is what it's looking for,
the proboscis never comes down, the fly doesn't eat.
But if I change it and put the head over plain water and
the feet over sugar water, even though it's only drinking plain water,
it's not satisfying its hunger, the fly eats.
So he was able to show with an experiment
that the fly actually tastes with its feet.
It's feet determines whether or not it is good to eat, not the head or
the proboscis or the mouth or even the smell, if the fly smells with the eyes.
It's the feet that determines whether the fly is eating or not.