Confidence intervals - Normal distribution Watch

science_geeks
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Hi everyone,

I'm really struggling with confidence intervals using normal distribution. Please can someone explain this to me.

Thank you
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kungfuslothy
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Do you have an example question?
(Original post by science_geeks)
Hi everyone,

I'm really struggling with confidence intervals using normal distribution. Please can someone explain this to me.

Thank you
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science_geeks
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(Original post by kungfuslothy)
Do you have an example question?
Yeah, Its this question hereName:  TSR .jpg
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kungfuslothy
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I'm a first-year Economics student and I'm assuming two-sided confidence interval means +/- answers
For a 95% confidence interval, the equation would be X+/-(zo/root n)
X - mean
z- critical value at 5% sig (which is 1.96 in this case)
o - standard deviation
n - sample size
So it would be 1465+/-((1.96*108)/root 20) = (1417.67, 1512.33)
I usually put the negative answer first in the brackets cause that's what the mark scheme says for me but idk for you.
(Original post by science_geeks)
Yeah, Its this question hereName:  TSR .jpg
Views: 19
Size:  78.2 KB
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science_geeks
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Ah yeah, I think you're right because the other questions I've seen only ask for 2 sided confidence intervals too. How do you find out what the critical value is at z? Is it by the % points table?

Also, just want to make sure but the relationship between standard deviation and variance is that the SD^2 = Var. Thank you so much though! That makes so much more sense

(Original post by kungfuslothy)
I'm a first-year Economics student and I'm assuming two-sided confidence interval means +/- answers
For a 95% confidence interval, the equation would be X+/-(zo/root n)
X - mean
z- critical value at 5% sig (which is 1.96 in this case)
o - standard deviation
n - sample size
So it would be 1465+/-((1.96*108)/root 20) = (1417.67, 1512.33)
I usually put the negative answer first in the brackets cause that's what the mark scheme says for me but idk for you.
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kungfuslothy
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The critical value is in the two tail probability table under the % points table
if it was 95% confidence you'd look under 0.05 etc
And yes root Variance = SD
(Original post by science_geeks)
Ah yeah, I think you're right because the other questions I've seen only ask for 2 sided confidence intervals too. How do you find out what the critical value is at z? Is it by the % points table?

Also, just want to make sure but the relationship between standard deviation and variance is that the SD^2 = Var. Thank you so much though! That makes so much more sense
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