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- [David] Raiders, hello.

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This video is about
analyzing visual evidence,

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but let's cut right to it.

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It's also about vampires.

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(spooky music)
(thunder booming)

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And we'll get to them,

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those cape wearing, widows peaked wonders

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of the mountains of Transylvania.

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But first, what do we even
mean by visual evidence?

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Like textual evidence, sure,

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we know what textual evidence is.

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It's written language.

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How do we know there's
potassium hydroxide in my soap?

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It's on the label.

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Ah, but how much potassium hydroxide?

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Visual evidence can tell us.

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Visual evidence includes the
graphs, charts, tables, images,

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and illustrations that
authors use in their texts.

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Authors include visual evidence

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to help readers better understand ideas

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because sometimes words just don't cut it.

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Visual evidence can help
strengthen a written argument

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and help express complicated ideas.

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So KOH, the potassium hydroxide,

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makes up 13.4% by weight of the soap.

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And sure it could list that
percentage on the label,

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but to my eye, seeing the number

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and the pie chart is more helpful.

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I can see at a glance

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that potassium hydroxide,
labeled here in red,

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only makes up a small part of my soap.

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This is useful because if
there were a lot more KOH

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than there already is,

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the soap would burn my
skin when I used it.

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Soap chemistry, visual evidence at work.

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Oftentimes, you will be asked
to evaluate visual evidence

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to see whether it supports

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or challenges an argument in a text.

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This is something you'll
have to do in many classes,

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history and science
classes as well as English.

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And questions about this
particular skill are common

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on standardized exams.

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So this brings us to vampires

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and specifically a very
complicated idea about vampires

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that some Norwegian researchers
wanted to test in 1994.

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Does garlic scare vampires away?

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This is a real study.

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They said something like,
according to folklore,

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garlic repels vampires.

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We wished to verify this,

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but owing to the lack of
vampires, we used leeches instead.

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Leeches, the real life
blood sucking worms.

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So like vampires, kinda.

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Based on the data,

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does garlic actually keep vampires away?

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Remembering that leches here
are our stand-ins for vampires.

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In a research setting,
the leches were presented

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with a hand smeared with garlic

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and a clean hand with the expectation

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that they would attach
themselves to one or the other.

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From our data, we conclude
that the relationship

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between vampires and garlic is blank.

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So here's the graph.

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What conclusions can you make

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about the traditional relationship

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between garlic and vampires?

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What does this graph say happens?

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What does the visual evidence tell you?

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I'm going to put a little music on.

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Feel free to pause the video and discuss

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or make your own guesses.

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Alright, see you in a bit.

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(soft music)

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So the title of this graph is:

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How Long Do Leeches Take to
Attach Themselves to a Hand?

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Right, and we have two bars
on the horizontal axis,

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the X axis.

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One is with garlic, the
other is without garlic.

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And over here on the Y
axis, the vertical axis,

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we can see that the legend reads seconds.

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That's how many seconds
the leches took to attach.

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This graph is potentially confusing

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because it might seem

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like the bigger bar is
the better one, right?

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But this is response time,

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how long do they take?

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So 14.9 seconds over here
versus 44.9 seconds over here.

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The shorter the response time,

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the faster the leach latches on.

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What can we conclude from
this study therefore,

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what was the main conclusion of the study?

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Well, basically the leeches went

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for the garlic covered hand,
the seasoned hand much faster,

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30 seconds faster on
average than they went

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for the unseasoned hand.

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That means they like
the garlicky hand more

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than the ungarlicky hand.

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And remember, tradition holds

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that garlic repels vampires,
it sends them away.

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So from the result of this
study, we can conclude

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that their tradition is wrong
and vampires love garlic,

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if vampires and leeches are the same.

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Yeah, it's a bit of a leap.

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Maybe this particular case feels silly.

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Fine, but this is a useful skill.

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You will be asked to
evaluate visual evidence

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to see whether it supports

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or challenges an argument in a text.

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A friend will send you an infographic

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about a political topic.

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You might look up stats
for your favorite athlete.

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You might have to puzzle
through a misleading graph

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on TV news.

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Understanding what data is trying

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to tell us is a core reading skill.

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Information, now it's got
numbers in it, trademark.

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And now you've got numbers in you.

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Nice work.

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Watch out for leeches.
You can learn anything.

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David out.