Using Standard Deviation
in AP Biology
Why would we use the standard
deviation to analyze our lab result?
• In statistics and probability theory,
standard deviation (represented by
the symbol σ ) shows how much
variation or " dispersion " exists from
the average (mean, or expected value)
• A low standard deviation (less than 2) indicates
that the data points tend to be very close to the
mean, whereas high standard deviation (greater than
2) indicates that the data points are spread out over a
large range of values.
What is the formula for standard
deviation?
Note: since our data is a sample, not a population, we will
use n-1 and not just n for our denominator.
What are the basic steps?
• Step 1-Find the mean of the data (in other
words, take an average of all your data points)
• Step 2-Subtract the mean from each data point
• Step 3- Square of the values you got in step 2
• Step 4-Subtract 1 from the number of data
points you used in step 1.
• Step 5- Divide your answer in step 3 by your
answer in step 4.
• Step 6 -Find the square root of the answer you
got in step 5.
Fun with standard deviation!
• Click on this website to access mathisfun.com
Use the standard deviation calculator on
this website to try your hand at standard
deviation problems!!
Youtube videos which help explain how to do
standard deviation:
Watch this video to give you the basic steps in
calculating standard deviation:
http://www.youtube.com/watch?v=klP8ElkVxJk
This video gives two ways to calculate standard deviation
(the computational formula is a little less work)
http://www.youtube.com/watch?v=_x-XWDEIhfE
Watch this one to help you do standard deviation on a
calculator:
http://www.youtube.com/watch?v=DMOXzwC2vzg
Watch this one on using microsoft excel to calculate
mean, variance and standard deviation:
http://www.youtube.com/watch?v=efdRmGqCYBk
How to use your calculator to
compute standard deviation
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Click on 2nd Stat button (above Data)
Hit right arrow button. You will see 1-var. This will help you get the standard deviation of a
sample.
Hit enter
Hit Data
When you see X1 submit your first data point. Hit enter
Then hit down arrow.
Your will see FRQ- Enter how many times the same data point shows up in your results.
Hit enter.
Use the down arrow. You will see X2. Submit your next data point. Hit enter.
When frequency shows up, enter the number of times that data point shows up in your
results. Hit enter.
After all data points and their frequency are entered, hit stat/var button on your calculator.
Use the right arrow to display mean and standard deviation.