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Statistics help!

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0123456789
Posts: 9226 - Karma: 148
so i have the zvalues, btu i need to find the p-values ising these. i know its kidna vague, but if anyone can help me out id be very greatful. pm me for more info on the problem.

if anyone wants to tell em how to find it thatd be great i cant find my notes eplainging it so thats pretty much all i need.

one more thing, if you know stats you probably know the bigass chart type thingy used for z values. do i just go to my z value(ie. 1.23) then find the corresponding value, and that corresponding value is my p-value?

thanks agian newschoolers, dont let me down!
Apr 14 2009 11:38PM
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0123456789
Posts: 9226 - Karma: 148
gah, i need help on another problem as well. i need to find the 75th percentile for a normal distribution curve. pm me if you got the lowdown on how to do that.
Apr 14 2009 11:40PM
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Uncle.Badness
Posts: 2545 - Karma: 55
60% of statistics are made up.
Apr 14 2009 11:41PM
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Jordan
Posts: 4079 - Karma: 2,122
Yeah I know what you are talking about.

Right now you only have Z scores?

I don't think you can find P with only a Z score.

Do you have standard deviation? or Alpha? How bout' n or a mean?


 
Apr 14 2009 11:44PM
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Tinga
Posts: 11349 - Karma: 2,333
totally just did my homework for this chapter.... except i copied it. do you know the population standard deviation? if you do you gotta use the standard normal distribution table if you only know the sample standard deviation you gotta use the degrees of freedom table.
Apr 14 2009 11:44PM
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0123456789
Posts: 9226 - Karma: 148
lets see for the first problem i have:
z-score
mu(mean)
std dev.

and i think thats it.

the only table i have from my book is the "areas under the standard normal distribution"


Apr 14 2009 11:48PM
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0123456789
Posts: 9226 - Karma: 148
whats alpha? i dont think we learned that one yet. our teacher showed us how to do it but i didnt get the notes due to being absent
Apr 14 2009 11:50PM
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InkShrink
Posts: 1079 - Karma: 30

Do you have the population std deviation or a sample std deviation?

Apr 14 2009 11:50PM
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Jordan
Posts: 4079 - Karma: 2,122
OH duh, my bad we did this in the start of the year.

Go to your Zscore table and find the corresponding number to your Z score.

That's your P value
Apr 14 2009 11:52PM
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Tinga
Posts: 11349 - Karma: 2,333
im guessing since the only table he has is the standard normal he has the population standard deviation. or he doesnt see the other table in his book.
Apr 14 2009 11:53PM
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Jordan
Posts: 4079 - Karma: 2,122
It should look like this:

Click for larger image

Just read across and find it.
Apr 14 2009 11:53PM
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0123456789
Posts: 9226 - Karma: 148
sweet, thats what i thought. + karma to all


and i think i have the 75th percentile figured out. but ill post if i dont
Apr 14 2009 11:53PM
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InkShrink
Posts: 1079 - Karma: 30
My professor won't let us use the table. It sucks.
Apr 14 2009 11:55PM
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Jordan
Posts: 4079 - Karma: 2,122
Using another online Z table it came out to .8907 which is not statistically significant at any reasonable alpha level.

I am not sure you've gotten there yet.
Apr 14 2009 11:56PM
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0123456789
Posts: 9226 - Karma: 148
you can do it easily with your calc, thats how i got it. if you have a ti-83/84 its superrrr easy to do.
Apr 14 2009 11:56PM
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Silence
Posts: 16030 - Karma: 150
Doesn't it matter if it's one tailed or 2 tailed?

I.e you are looking for either the top or bottom 25%, OR you could be looking for the probability it is either in the top 12.5% or the bottom 12.5%,. depending on the question
Apr 14 2009 11:57PM
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Dr_Feelgood
Posts: 1176 - Karma: 15
that looks gay. im so happy im done with math FOREVER. muahahahahha
Apr 14 2009 11:57PM
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Jordan
Posts: 4079 - Karma: 2,122
Ummm you can't be serious, you have to memorize values from -3.4 to 3.4?

I know they are related in terms of going up, but still that sucks!
Apr 14 2009 11:57PM
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DHogg
Posts: 3462 - Karma: 237
The P-value is just  the lowest level of significance that would lead to rejection of the null hypothesis.
There not really an equation for finding it, but it is the probability found in either the z-table or t-table associated with either the calculated z-value or calculated t-value.
For example, Suppose your calculated z-value is -1.86, your p-value is 0.0314. This is right out of the Z table
Apr 14 2009 11:59PM
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InkShrink
Posts: 1079 - Karma: 30
It is, I actually have a stat exam on Thursday, but sometimes I'm lazy and just want to use the table.
Apr 14 2009 11:59PM
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Jordan
Posts: 4079 - Karma: 2,122
That'd be statistically significant at a .05 alpha level and you would reject the null hypothesis.
Apr 15 2009 12:01AM
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0123456789
Posts: 9226 - Karma: 148
word, i wasnt sure if it was right out of the table, or if i had to do some other calculations.
Apr 15 2009 12:01AM
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DHogg
Posts: 3462 - Karma: 237
indeed. yeah i didnt really finish that off
Apr 15 2009 12:14AM
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