Since the question has been raised as to whether or not enough data points have been acquired I have undertaken another power analysis.
Read about power analysis here:
http://en.wikipedia.org/wiki/Statistical_power
And using this program for performing power analysis:
http://biostat.mc.vanderbilt.edu/wik...owerSampleSize
Read about Student's
t test statistic here:
http://en.wikipedia.org/wiki/Student%27s_t-test
Refer to the Wikipedia article on Power Analysis understand '
power' as used in the program. I set the
power value to
0.80, or 80 percent,which is a generally accepted power used in the design of studies for the testing of drugs and Class III medical devices in the United states.
In short and with a fair degree of arguable word choices, a
power analysis, as I used it for my most recent study posted yesterday, uses data from two historical sets of data points to determine how many sampling events should be conducted in a future experiment.
Power analysis can also be applied in the analysis of historical data sets to determine whether or not they contain enough data points to have a certain degree of statistical confidence that the two data sets are different.
'
Paired' data sets contain equal number of measurements. In the figure reproduced below the data sets for each test article contain the results of 5 measurements, thus they are 'paired'.
alpha as used in the program is this:
http://statistics.about.com/od/Infer...d-P-Values.htm
In these analyses I have been using an
alpha of 0.05.
The '
p' value is, again with a lot of interpretation to make it understandable here, a measure of the degree of statistical confidence that two sets of data points are truly different.
P values less than alpha are generally considered to be '
statistically significant'. The smaller the
p value, the more significant the difference. Small
p values make physicians happy. For instance, a
p value of 0.001 is considered to be more significant than a
p value of 0.05.
Delta is defined as:
A difference in population means. In the case of the data above it is the difference between the means of the measurements between Maker 1 and Maker 3 or
In the program select the second tab 't-test' and you will see the input page that I used. In the first pull-down box from the top I selected 'sample size'. In the second pull down box from the top I selected '
paired' because my data sets have 5 measurements each and are thus '
paired'.
In the next pane on the left I entered 0.05 for
alpha. Below that I entered 0.80 for '
power'. On the right side of that pane I entered the value for
delta and below that I entered the value for
sigma.