- [David] Raiders, hello.
This video is about analyzing visual evidence,
but let's cut right to it.
It's also about vampires.
(spooky music) (thunder booming)
And we'll get to them,
those cape wearing, widows peaked wonders
of the mountains of Transylvania.
But first, what do we even mean by visual evidence?
Like textual evidence, sure,
we know what textual evidence is.
It's written language.
How do we know there's potassium hydroxide in my soap?
It's on the label.
Ah, but how much potassium hydroxide?
Visual evidence can tell us.
Visual evidence includes the graphs, charts, tables, images,
and illustrations that authors use in their texts.
Authors include visual evidence
to help readers better understand ideas
because sometimes words just don't cut it.
Visual evidence can help strengthen a written argument
and help express complicated ideas.
So KOH, the potassium hydroxide,
makes up 13.4% by weight of the soap.
And sure it could list that percentage on the label,
but to my eye, seeing the number
and the pie chart is more helpful.
I can see at a glance
that potassium hydroxide, labeled here in red,
only makes up a small part of my soap.
This is useful because if there were a lot more KOH
than there already is,
the soap would burn my skin when I used it.
Soap chemistry, visual evidence at work.
Oftentimes, you will be asked to evaluate visual evidence
to see whether it supports
or challenges an argument in a text.
This is something you'll have to do in many classes,
history and science classes as well as English.
And questions about this particular skill are common
on standardized exams.
So this brings us to vampires
and specifically a very complicated idea about vampires
that some Norwegian researchers wanted to test in 1994.
Does garlic scare vampires away?
This is a real study.
They said something like, according to folklore,
garlic repels vampires.
We wished to verify this,
but owing to the lack of vampires, we used leeches instead.
Leeches, the real life blood sucking worms.
So like vampires, kinda.
Based on the data,
does garlic actually keep vampires away?
Remembering that leches here are our stand-ins for vampires.
In a research setting, the leches were presented
with a hand smeared with garlic
and a clean hand with the expectation
that they would attach themselves to one or the other.
From our data, we conclude that the relationship
between vampires and garlic is blank.
So here's the graph.
What conclusions can you make
about the traditional relationship
between garlic and vampires?
What does this graph say happens?
What does the visual evidence tell you?
I'm going to put a little music on.
Feel free to pause the video and discuss
or make your own guesses.
Alright, see you in a bit.
(soft music)
So the title of this graph is:
How Long Do Leeches Take to Attach Themselves to a Hand?
Right, and we have two bars on the horizontal axis,
the X axis.
One is with garlic, the other is without garlic.
And over here on the Y axis, the vertical axis,
we can see that the legend reads seconds.
That's how many seconds the leches took to attach.
This graph is potentially confusing
because it might seem
like the bigger bar is the better one, right?
But this is response time,
how long do they take?
So 14.9 seconds over here versus 44.9 seconds over here.
The shorter the response time,
the faster the leach latches on.
What can we conclude from this study therefore,
what was the main conclusion of the study?
Well, basically the leeches went
for the garlic covered hand, the seasoned hand much faster,
30 seconds faster on average than they went
for the unseasoned hand.
That means they like the garlicky hand more
than the ungarlicky hand.
And remember, tradition holds
that garlic repels vampires, it sends them away.
So from the result of this study, we can conclude
that their tradition is wrong and vampires love garlic,
if vampires and leeches are the same.
Yeah, it's a bit of a leap.
Maybe this particular case feels silly.
Fine, but this is a useful skill.
You will be asked to evaluate visual evidence
to see whether it supports
or challenges an argument in a text.
A friend will send you an infographic
about a political topic.
You might look up stats for your favorite athlete.
You might have to puzzle through a misleading graph
on TV news.
Understanding what data is trying
to tell us is a core reading skill.
Information, now it's got numbers in it, trademark.
And now you've got numbers in you.
Nice work.
Watch out for leeches. You can learn anything.
David out.