# Thread: Calculating z-score/confidence interval with benford's law

1. ## Calculating z-score/confidence interval with benford's law

Hey guys, as you can probably read from my username, bendfordhates,

I have been stuck on my last introductory statistics assignment question for the past few days and I have no idea what to do.

Anyhow, I received a 200 data set covering a whole population. The question asked me to determine if the dataset followed the law, graph it, compare and contrast and lastly 'set up the CI and z-score for each first digit classification (1-9) separately'.

I have completed the first few sections of the question but cannot seem to understand/grasp how to find the CI and z-score on excel. My two major uncertainties include:
1. How do I find the standard deviation
for each first digit classification (1-9) separately? I tried to calculate the SD of only the numbers with 1 as the first integer but that doesn't seem to help.
2. What is the excel command for calculating z-score and which rows/columns do I highlight? Currently I have the columns: data, first integer, count, sample ratio, benford ratio, difference between ratios.
- I just can't seem to calculate the standard deviation which also means I cant calculate the upper and lower limits.

Sorry for the ramble, but thanks in advance!

Cheers guys

2. Good evening,

I'm a bit rusty on my statistics, but I think to calculate standard deviation you would use something like:

Deviation = Value [A1 for example] - AVERAGE (All Values [ex: \$A\$1:\$A\$300] )

Best of luck,

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