Discussion 6-30

# Discussion 6-30 - JT Ch 5 Q 12 or 15 Megan Goldman Reliable...

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JT: Ch 5 Q 12 or 15 Megan Goldman: Reliable also needs to take into account the correlation. .. even if you're inside the range of the original data, if the association is fairly weak your guess may be not that great. Megan Goldman: If it's extrapolation, I'd go with "rather dubious." On interpolation with strong assocation (fairly high r), I'd go with "quite reliable". Interpolation with a weaker assocation, I'd say "possible justified". Megan Goldman: r = .59 isn't anything to write home about. JT: ok thanks Tiffany: so megan is there a time when it does matter if regression of x on y or vice versa Tiffany: like does it ever change any properties Megan Goldman: It matters very much. The slope will change! Tiffany: bc of which one we divide by right Megan Goldman: If you're predicting Y using X, the slope is (r * sdy)/sdx. However, if you're predicting X using Y, then it's (r * sdx)/sdy. .. the roles of x and y reverse. Megan Goldman: Exactly. Tiffany: oh okay well im going to read about ch. 6, i know you got a lot of questions about that Megan Goldman: So, if you've done a regression and found Y = slope * X + intercept, and then you're given a value of Y, do NOT use this equation to predict X! Tiffany: is there any way to look at the earlier conversations Tiffany: maybe someone ask the same question Megan Goldman: You'd need to re-run and get X = slope * Y + intercept. Megan Goldman: Not that I've found. I'd imagine over the net day or so people will start asking Ch 6 questions on the discussion board, and so hints will start popping up there as well. Megan Goldman: Hi melinda and Anna. melinda: hi Megan. can i ask u a few questions about ch.4 hwk? melinda: hi Megan Goldman: Sure. Anna Park: hello Anna Park: i also have questions about the chapter 4 homework

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Megan Goldman: Okay. melinda: my first question is about q8. ..i have submitted four times and put that the graph was no b/c of nonlinearity and association being weak which was wrong. ..i think it might also be hetero. ..not really sure. ..the link for my graph is http://s294.photobucket.com/albums/mm118/melindakhoshabe/? Megan Goldman: Let me try to pull that up. melinda: okay thanks for the help Anna Park: yeah my graph sort of looks like that and i'm having trouble with that question too Tiffany: dont put weak association Megan Goldman: heh, this is exactly the graph Serene was looking at earlier. Megan Goldman: Tiffany is our resident expert on this problem. ;-) Tiffany: yeah i hate those graphs melinda: could you help me in how to approach the answers to this problem? Tiffany: it took 2 gsi and the professor Tiffany: haha im very bitter about these graphs Anna Park: i am nearing that sentiment melinda: tiffany are u sure not to put weak assocaition, can u look at my graph melinda: so what should i put for this problem? Tiffany: if it is weak
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Discussion 6-30 - JT Ch 5 Q 12 or 15 Megan Goldman Reliable...

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