Standard Deviation Flashcards
What does standard deviation tell you.
Measure of spread of values about the mean.
How much the values in single sample vary.
What does 9 +_ 3 mean ?
9 is mean and standard deviation is 3.
So most values spread between 6 and 12.
As the SD is the spread of values about the mean.
What does a narrow graph show ?
Values are similar and close to mean.
Little variation.
SD is small.
What does a wide graph show ?
Values aren’t similar and not all close to mean.
A lot of variation.
SD is large.
Example.
Woodland A - mean 26 and SD 3.
Woodland B - mean 32 and SD 9.
Trees generally taller in woodland B and but greater variation.
Compared to woodland A.
SD is method of calculating what ?
The dispersion of data
What is another method of calculating the dispersion of data ?
Range.
Difference between highest and lowest figures.
Why is SD more useful than the range?
It takes into account all the values in the data set, whereas range uses only 2.
So range could be more affected by anomalous result.
How can SD be plotted on graph or chart?
Error bars
What are error bars?
They extend one SD above and one SD below the mean.
The longer the SD bar …
The larger the SD and more spread about the mean.
