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

Thank you sir.