Analyzing one categorical variable
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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.