The Professor's Response

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Hello, Mr. McGuckian. For the homework problems in 9.8 (#35 and 36), I am getting he correct answer but the wrong sign. For example for #36, the answer is (1.21, 7.54). But I got (-1.21, -7.54). I was wondering why this was.
Thanks.

Hi Carmen,

This is a result of performing your subtraction in the opposite order of how I performed my subtraction. This starts with your expression of the claim and how you relate the two means in that step. Watch the video below for a general explanation of what is causing the different signs, and why it doesn't matter.

Professor McGuckian

Hi Carmen,

For the specific question you are asking about, the subtraction of the before and after matters greatly. If your subtraction was done First Score - Second Score but mine was done Second Score - First Score, your answer will be opposite of mine. The interpretation is what matters though, not the order. If your interval is negative and you did First - Second, the interpretation is that the Second set of scores is larger (since the interval is negative). In my interval it is entirely positive, so I would say the first mean is larger, but the first mean in my subtraction is the Second score. In the end, we both have the exact same result. It just looks different in terms of the sign because of the different order of the subtraction.

Hope that helps,

Professor McGuckian

That is correct Sandra. There is not a statistically significant difference between the two population means.