They are a graphical representation of the variability of the data
What is standard deviation for?
Summarize the spread of values around the mean. 68% of the values fall within one SD of the mean.
How much data falls within 2 SD of the mean?
98%
What does a small standard deviation mean?
Data is clustered around the mean value.
What does a large standard deviation mean?
There is a wider spread around the mean.
What does the t-test do?
It uses the standard deviations of both sets of data to deduce the significance of the difference.
It helps scientists work out if the difference is significant or not.
What are the 'degrees of freedom' if you have 2 samples, both with a population of 10?
Degrees of freedom are the sum of the samples ize of each of the two groups minus 2.
For example, if two groups of 10 plants each are being looked at, then 10 plus 10 is 20 minus 2 is 18. Thus, the number to look at in the ‘Degrees of freedom’ column is 18.