# [R] How to Calculate Percentage of Data within certain SD of Mean

Pete Brecknock Peter.Brecknock at bp.com
Sun Feb 5 22:13:03 CET 2012

```How about ....

# Calculate Stats
total = length(nb10[,1])
mean = mean(nb10[,1])
sd = sd(nb10[,1])

# Function ... nSD is the number of SD you are looking at
pData <- function(nSD){
lo = mean - nSD/2*sd
hi = mean + nSD/2*sd
percent = sum(nb10[,1]>=lo & nb10[,1]<=hi)/total *100
}

# Output ...
print(paste("Percent of data within 2 SD is ",pData(2),"%", sep=""))  # 86%
print(paste("Percent of data within 3 SD is ",pData(3),"%", sep=""))  # 93%
print(paste("Percent of data within 4 SD is ",pData(4),"%", sep=""))  # 96%
print(paste("Percent of data within 5 SD is ",pData(5),"%", sep=""))  # 97%
print(paste("Percent of data within 6 SD is ",pData(6),"%", sep=""))  # 98%

HTH

Pete

Ajata Paul wrote
>
> How do you calculate the percentage of data within 2SD, 3SD, 4SD, 5SD, and
> 6SD of the mean?  I used the following link as the data I'm working with:
> this helps answer my question.  Can you please explain how to calculate
> the SD's?  Please be specific in which part of the function changes when
> calculating the next SD up.
>
> Thanks.
>

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