Standard Deviation in Excel
14
October

By Adem Lewis / in , , /


Hi everybody, I didn’t get class time in
class to talk about standard deviation and how to calculate that so I wanted to
record this quick video to help you out. There are lots of
different ways that you can calculate standard
deviation. One is by hand and if you’re in a stats class you’ll do that. If
you’re in our class, you generally want to avoid that. Your
regular scientific calculators that you can use in lab and on exams all have the
capability and I’ll show you some of that in class. Today, I want to show you
what I think is an easier way if you’re at home and near a computer so I’m gonna
go ahead and use office 365 for this since we now all have access to this
through the school. I’ve just logged into the the “my
portal” dashboard. if you go to the website and click on “my portal” this is how we access our email. So I’ve logged
in and I scroll down here to the Microsoft Office 365. If you just
click the Microsoft Excel it’ll open it up and then this is really cool how easy
this is to do so just go to new blank worksheet and it’ll open up an instance
of Excel that you can go ahead and type in so here’s the spreadsheet and the first
thing you just need to do is enter your data points so we will just type data
in this cell and you can start anywhere you want here. We’re just gonna type in
some data let’s just type in 1.1 1.2 and 1.4 and those would be our data points
so if you’re listing these on your lab we would list these as X 1
X 2 and X 3 just in other words data point number
one is 1.1 data point number two is 1.2 and data point
number three is 1.4, so that’s our data. Now we want to calculate the
average the standard deviation and abbreviation we often use for standard
deviation is stdev. You’ll see why we use that later, and last, the percent
relative standard deviation. So I’m just gonna put those labels here and I’m
going to show you how to calculate it It’s really straightforward you just put
your cursor in the area that you want to calculate it and you type
equals which tells Excel that we’re going to type in a formula we’re going
to tell it to do a calculation and then we type the word average and you can see
that that Excel knows that this is a calculation that it’s gonna do and then
we open the parentheses and we highlight the things that we want to calculate the
average of and then we close the parentheses and push enter and well now
in this cell calculate the average of the cells that we highlighted. Now we do
the same thing for standard deviation in Excel the function for standard
deviation is stdev. It’s that abbreviation. Now, there are some
variations on this that you can learn about if you want later. We just need to
type in the standard “stdev” and Excel knows what to do so equals stdev we
open parentheses and highlight the cells that we’re interested in close
parentheses hit enter and that should calculate the standard deviation in the
cell so for our data set here we it has an average of 1.23333 and a standard deviation of 0.1527 now the relative standard
deviation is just the standard deviation divided by the average in percent form
so to do that we again just type in equals to tell it we wanted to calculate
something and then we click on the cell standard deviation then we use the
divided by sign the slash to be divided by.
Then we click on the cell that was the average so it’s the standard deviation
cell E6 divided by the average cell which was E5. Now what you’ll
notice as soon as we click on that is that’s a decimal form so you could have
multiplied it by a hundred, but Excel has a better way to do to convert it to the
percent form and that’s just by coming up here to the menus and saying hey we
wanted that to be in percent form so there you go it’s all calculated for us
the average standard deviation and percent relative standard deviation. So
that’s it one very last thing is if you were going to report the average and
standard deviation for this we need to then round four significant figures so
if we’re going to report the average and the standard deviation, the way that we actually write that down
on your paper and I’ll just type in the cell but the way you would write that
down on your paper is you would go ahead and round to 1.2 instead of
1.23333 because they were all two significant digit numbers
and then we would use the plus or minus key which in Excel you can just type + /
– in Microsoft Word it has a special symbol for that if you prefer to use it.
Then we actually round the standard deviation only to the to the same
decimal place as we rounded the average so you would do 1.2. Oops!
back in the cell we can come up here you can always come up to this function line
to edit if you need a little bit more space so we would type in 1.2
plus or minus and then 0.2 rounding off the standard deviation to
the same decimal place as we did the average. So then that’s how you report
the average and standard deviation if you want it to type in your final answer that’s it thank you very much


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