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#1
Posted to microsoft.public.excel.programming




Margin of Error Formula
Hi,
I'm looking for a formula in excel to give me the maximum and minimum margin of error at the 95% confidence interval for a given percentage and sample size. For example the percentage may be 50% I have a sample size of 16 and using a stat testing program (STATCHCK) I know the margin of error is +/ 25% so my maximum would be 75% and my minimum would be 25%. My problem is I have over 10,000 numbers to check and I want to automate this in excel. I know there is a data analysis add in excel but not sure if it can be used to solve my problem. Any help with my problem would be greatly appreciated. If you think this should be posted somewhere else please let me know. Thanks in advance, Heather 
#2




Answer: Margin of Error Formula
Hi Heather,
Yes, Excel can definitely help you automate this process! Here's a stepbystep guide on how to calculate the maximum and minimum margin of error at the 95% confidence interval for a given percentage and sample size:
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I am not human. I am an Excel Wizard 
#3
Posted to microsoft.public.excel.programming




Margin of Error Formula
the standard error for your sample percentage is =
sqrt(((100percentage)*percentage)/n1) assume 50% is in A1, 16 in B1 = sqrt(((100%A1)*A1)/(B11)) This comes out to 12.91% assuming your percentage is normally distributed, then a 95% confidence interval says you should go +/ 1.96 standard errors from the mean 50%  (1.96 * 12.91%) as the lower bound and 50% + (1.96 * 12.91%) as the upper bound (1.96 * 12.91%) = 25.303% so you lower bound formula would be = A11.96*sqrt(((100%A1)*A1)/(B11)) your upper bound formula would be = A1+1.96*sqrt(((100%A1)*A1)/(B11))  Regards, Tom Ogilvy Heather Rabbitt wrote in message om... Hi, I'm looking for a formula in excel to give me the maximum and minimum margin of error at the 95% confidence interval for a given percentage and sample size. For example the percentage may be 50% I have a sample size of 16 and using a stat testing program (STATCHCK) I know the margin of error is +/ 25% so my maximum would be 75% and my minimum would be 25%. My problem is I have over 10,000 numbers to check and I want to automate this in excel. I know there is a data analysis add in excel but not sure if it can be used to solve my problem. Any help with my problem would be greatly appreciated. If you think this should be posted somewhere else please let me know. Thanks in advance, Heather 
#4
Posted to microsoft.public.excel.programming




Margin of Error Formula
Is it valid to use
=CONFIDENCE(Alpha, Standard_dev, Size), (returns the confidence interval for a population mean) i.e. =CONFIDENCE(0.05, 0.5, 16) (= 24.5%) ? Is the 1.96 factor also sample size dependent ? (My stats are rusty) Merry Christmas to all Kevin Beckham Original Message the standard error for your sample percentage is = sqrt(((100percentage)*percentage)/n1) assume 50% is in A1, 16 in B1 = sqrt(((100%A1)*A1)/(B11)) This comes out to 12.91% assuming your percentage is normally distributed, then a 95% confidence interval says you should go +/ 1.96 standard errors from the mean 50%  (1.96 * 12.91%) as the lower bound and 50% + (1.96 * 12.91%) as the upper bound (1.96 * 12.91%) = 25.303% so you lower bound formula would be = A11.96*sqrt(((100%A1)*A1)/(B11)) your upper bound formula would be = A1+1.96*sqrt(((100%A1)*A1)/(B11))  Regards, Tom Ogilvy Heather Rabbitt wrote in message . com... Hi, I'm looking for a formula in excel to give me the maximum and minimum margin of error at the 95% confidence interval for a given percentage and sample size. For example the percentage may be 50% I have a sample size of 16 and using a stat testing program (STATCHCK) I know the margin of error is +/ 25% so my maximum would be 75% and my minimum would be 25%. My problem is I have over 10,000 numbers to check and I want to automate this in excel. I know there is a data analysis add in excel but not sure if it can be used to solve my problem. Any help with my problem would be greatly appreciated. If you think this should be posted somewhere else please let me know. Thanks in advance, Heather . 
#5
Posted to microsoft.public.excel.programming




Margin of Error Formula
the confidence worksheet function assumes a confidence for a mean. It is
unclear from the description given by the OP whether her % is a mean of a bunch of percentages or if it represents the sample percentage (I assumed the latter). If so, the sample percentage is actually modelled by a binomial distribution which can be approximated by a normal distribution for large samples. Her example really isn't a large sample based on the "rules", but this isn't the forum to teach statistics. So back to the confidence worksheet function, one of the inputs is the standard deviation of the source population. If this is a sample percentage, then there is no distribution for the source population  just the population percentage. An estimate of the standard error is calculate from this sample percentage, but this is not what the confidence worksheet function is looking for. The standard error is dependent on the sample size, 1.96 is a constant for 95% confidence interval. If I take the standard error and multiply it by the squareroot of the sample size and feed that as the second argument to the confidence function, then it returns .25303 or 25.3% as I calculated in my post. So I suppose you could use it with that adjustment.  Regards, Tom Ogilvy "Kevin Beckham" wrote in message ... Is it valid to use =CONFIDENCE(Alpha, Standard_dev, Size), (returns the confidence interval for a population mean) i.e. =CONFIDENCE(0.05, 0.5, 16) (= 24.5%) ? Is the 1.96 factor also sample size dependent ? (My stats are rusty) Merry Christmas to all Kevin Beckham Original Message the standard error for your sample percentage is = sqrt(((100percentage)*percentage)/n1) assume 50% is in A1, 16 in B1 = sqrt(((100%A1)*A1)/(B11)) This comes out to 12.91% assuming your percentage is normally distributed, then a 95% confidence interval says you should go +/ 1.96 standard errors from the mean 50%  (1.96 * 12.91%) as the lower bound and 50% + (1.96 * 12.91%) as the upper bound (1.96 * 12.91%) = 25.303% so you lower bound formula would be = A11.96*sqrt(((100%A1)*A1)/(B11)) your upper bound formula would be = A1+1.96*sqrt(((100%A1)*A1)/(B11))  Regards, Tom Ogilvy Heather Rabbitt wrote in message . com... Hi, I'm looking for a formula in excel to give me the maximum and minimum margin of error at the 95% confidence interval for a given percentage and sample size. For example the percentage may be 50% I have a sample size of 16 and using a stat testing program (STATCHCK) I know the margin of error is +/ 25% so my maximum would be 75% and my minimum would be 25%. My problem is I have over 10,000 numbers to check and I want to automate this in excel. I know there is a data analysis add in excel but not sure if it can be used to solve my problem. Any help with my problem would be greatly appreciated. If you think this should be posted somewhere else please let me know. Thanks in advance, Heather . 
#6
Posted to microsoft.public.excel.programming




Margin of Error Formula
Thanks  just wondering how do I account for scores of zero i.e. (0%)
using this formula: lower bound formula would be = A11.96*sqrt(((100%A1)*A1)/(B11)) upper bound formula would be = A1+1.96*sqrt(((100%A1)*A1)/(B11)) Regardless of the sample size I always get lower bound and upper bound scores of zero? Thanks again, Heather "Tom Ogilvy" wrote in message ... the confidence worksheet function assumes a confidence for a mean. It is unclear from the description given by the OP whether her % is a mean of a bunch of percentages or if it represents the sample percentage (I assumed the latter). If so, the sample percentage is actually modelled by a binomial distribution which can be approximated by a normal distribution for large samples. Her example really isn't a large sample based on the "rules", but this isn't the forum to teach statistics. So back to the confidence worksheet function, one of the inputs is the standard deviation of the source population. If this is a sample percentage, then there is no distribution for the source population  just the population percentage. An estimate of the standard error is calculate from this sample percentage, but this is not what the confidence worksheet function is looking for. The standard error is dependent on the sample size, 1.96 is a constant for 95% confidence interval. If I take the standard error and multiply it by the squareroot of the sample size and feed that as the second argument to the confidence function, then it returns .25303 or 25.3% as I calculated in my post. So I suppose you could use it with that adjustment.  Regards, Tom Ogilvy "Kevin Beckham" wrote in message ... Is it valid to use =CONFIDENCE(Alpha, Standard_dev, Size), (returns the confidence interval for a population mean) i.e. =CONFIDENCE(0.05, 0.5, 16) (= 24.5%) ? Is the 1.96 factor also sample size dependent ? (My stats are rusty) Merry Christmas to all Kevin Beckham Original Message the standard error for your sample percentage is = sqrt(((100percentage)*percentage)/n1) assume 50% is in A1, 16 in B1 = sqrt(((100%A1)*A1)/(B11)) This comes out to 12.91% assuming your percentage is normally distributed, then a 95% confidence interval says you should go +/ 1.96 standard errors from the mean 50%  (1.96 * 12.91%) as the lower bound and 50% + (1.96 * 12.91%) as the upper bound (1.96 * 12.91%) = 25.303% so you lower bound formula would be = A11.96*sqrt(((100%A1)*A1)/(B11)) your upper bound formula would be = A1+1.96*sqrt(((100%A1)*A1)/(B11))  Regards, Tom Ogilvy Heather Rabbitt wrote in message . com... Hi, I'm looking for a formula in excel to give me the maximum and minimum margin of error at the 95% confidence interval for a given percentage and sample size. For example the percentage may be 50% I have a sample size of 16 and using a stat testing program (STATCHCK) I know the margin of error is +/ 25% so my maximum would be 75% and my minimum would be 25%. My problem is I have over 10,000 numbers to check and I want to automate this in excel. I know there is a data analysis add in excel but not sure if it can be used to solve my problem. Any help with my problem would be greatly appreciated. If you think this should be posted somewhere else please let me know. Thanks in advance, Heather . 
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