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12-14-2005, 04:04 AM
Post subject: how do i find... (math, statistics ques)
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#1 (permalink)
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Straight
Join Date: Jan 2005
Location: MA
Posts: 144
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the z-critical value appriopriate for a 97% confidence interval?
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WildBobAA
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4-of-a-Kind
Join Date: Aug 2005
Location: lol i dunno
Posts: 1,811
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You have to look at a normal distribution table.
http://people.hofstra.edu/faculty/St...rmaltable.html
You'd add .5 to the values in the table to get the confidence level.
Example: The z critical value .10 would have a 0.5398 confidence level.
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Straight
Join Date: Jan 2005
Location: MA
Posts: 144
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my book has z critical values for confidence intervals...
90% is 1.645
95% is 1.96
98% is 2.33
99% is 2.58
99.8% is 3.09
99.9% is 3.29
I need 97%...
I dont really understand what your saying bob, it doesnt seem to work...
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gengar
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Join Date: Dec 2005
Location: Henderson, NV
Posts: 88
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Use the link that WildBob provided, and use the chart backwards.
You want 97%. The graph starts at the middle (50%) and counts up from there, so for 97% you need 47%. So find the lowest value for 47%... there is a value for .4699, which corresponds to 1.88... so you know that 1.882 or so should do it. And there you go.
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Demiparadigm
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4-of-a-Kind
Join Date: Feb 2005
Location: Party 6 max
Posts: 1,602
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http://www.flopturnriver.com/phpBB2/...=188609#188609
not exactly what you're looking for...
what are you looking for?
EDIT: I think I figured out what you wanted...
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midas06
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4-of-a-Kind
Join Date: Jun 2005
Location: NZ
Posts: 2,196
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Half of 0.97 = 0.485.
Using the CI table, z=2.17
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WildBobAA
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4-of-a-Kind
Join Date: Aug 2005
Location: lol i dunno
Posts: 1,811
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Quote:
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Originally Posted by midas06
Half of 0.97 = 0.485.
Using the CI table, z=2.17
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No it's not half you add .5 to the values.
Gengar is right. All the area less than zero corresponds to half the area under the normal curve. And the table I linked gives the area from zero to whatever z value you use it for. If you're having a problem reading the table, the z-values are listed on the very left/top of the table. The the ones/tenths values are listed on the left and the hundreths values are listed on the top. So if you wanted to look up the confidence interval for 1.12, you'd look on the left side for the row labled 1.1 and then go right to the column labled 0.02 and add .5 to the value there and that would give you the confidence interval.
So since you're looking for the .97 confidence interval look on the graph for .47 (.47 + .5 = .97). Which (like gengar said) is about 1.88.
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Straight
Join Date: Jan 2005
Location: MA
Posts: 144
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Quote:
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Originally Posted by WildBobAA
Quote:
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Originally Posted by midas06
Half of 0.97 = 0.485.
Using the CI table, z=2.17
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No it's not half you add .5 to the values.
Gengar is right. All the area less than zero corresponds to half the area under the normal curve. And the table I linked gives the area from zero to whatever z value you use it for. If you're having a problem reading the table, the z-values are listed on the very left/top of the table. The the ones/tenths values are listed on the left and the hundreths values are listed on the top. So if you wanted to look up the confidence interval for 1.12, you'd look on the left side for the row labled 1.1 and then go right to the column labled 0.02 and add .5 to the value there and that would give you the confidence interval.
So since you're looking for the .97 confidence interval look on the graph for .47 (.47 + .5 = .97). Which (like gengar said) is about 1.88. |
how can it be 1.88 when 95% is 1.96... i mean, the value must be between 1.96 and 2.33...
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WildBobAA
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4-of-a-Kind
Join Date: Aug 2005
Location: lol i dunno
Posts: 1,811
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Oh ok I know now. You're looking for the "middle" .97 in area not the left .97 in area.
Ok so then to use the chart you'd take (1 - .97) = .03. .03/2 = .015. then take .5 - .015 = .485 and find that on the chart.
So it is 2.17. midas was correct, I apologize.
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