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## Analyzing one categorical variable

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# Reading pictographs

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## Video transcript

According to the
pictograph below, how many survey respondents
have type O positive blood? How many have O negative blood? So a pictograph is
really just a way of representing
data with pictures that are somehow
related to the data. So in this case, they
gave us little pictures of, I'm assuming, blood
drops right over here. And then they tell us that each
blood drop in this pictograph represents 8 people. So you could kind of view that
as a scale of these graphs. Each of these say 8 people. So, for example, if you say how
many people have A positive? It would be 1, 2, 3,
4, 5, 6, 7 blood drops. But each of those blood
drops represent 8 people, so it would be 56 people
have type A positive. But let's answer
the actual question that they're asking us. How many survey respondents
have type O positive? So this is O, and then
we care about O positive. So we have 1 blood drop, 2, 3. I'm going to do this in
a new, different color. We have 1, 2, 3, 4, 5, 6, 7, 8. So we have 8 drops. I'll put those in quotes because
they're pictures of drops. And then the scale is 8 people. Let me write it this way. Times 8 people per drop. And so 8 times 8-- and
actually even the drops, you could view them
as canceling out if you view them as
units, so drops, drops. 8 times 8 is equal to 64 people. So they could have written
literally the number 64 right over here. 64 people have type
O positive blood. Now let's think about
the O negative case, O negative blood. Well, this is O. And then
within the blood group O, this is O negative. And we have 1 drops, 2 drops. So we have 2 drops
times 8 people per drop. And so 2 times 8, each
of these represent 8. So 8 and then 16, or 2 times
8 is equal to 16 people. So 16 of the survey respondents,
16 have type O negative. 64 have type O positive.