## Small Sample Statistics

## Small Sample Statistics

(OP)

Greetings,

I made the following measurements:

4.10, 3.98, 4.86, 4.39, 4.57, 4.44

I am being asked "what is the error." Thery want to know what the +/- is on my numbers. I have averaged them (4.39) and said +/- 2SD. I am tracking changes - so I will make these same measurements under a different condition and want to know if they are statistically different. But at the new condition I will only have two values.

How can I answer this? And does it make a difference if I discard the first two results (procedural error).

Thanks.

I made the following measurements:

4.10, 3.98, 4.86, 4.39, 4.57, 4.44

I am being asked "what is the error." Thery want to know what the +/- is on my numbers. I have averaged them (4.39) and said +/- 2SD. I am tracking changes - so I will make these same measurements under a different condition and want to know if they are statistically different. But at the new condition I will only have two values.

How can I answer this? And does it make a difference if I discard the first two results (procedural error).

Thanks.

## RE: Small Sample Statistics

## RE: Small Sample Statistics

There is another way, namelly to estimate the inerval where the average will be found with a certain probability:calculate the average(=4,39) and stdev(=0,3187),

number of degrees of freedom N-1 (=5) and from tables find out the value of student`s t for double sided alfa=0,01(=3,36)and calculate the term t*stdev/sqrt(N-1)(=3,36*0,3187/2,36)=0,478.

So your average value will be 98% likely in the range 4,39-0,478...4,39+0,478.

You can find the student`s t in excel:

choose confidence limits CL[%]

calculate alfa=(100-CL)/100

call TINV(alfa, N-1)

m777182

## RE: Small Sample Statistics

For SWC.... here's the story. I have a single value at many (~50) conditions. I've been asked to repeat one condition ~10 times to "determine the scatter." Soon I will have 12 values at condition X. The confidence limits and student't t-test is where I was leaning.

It is not practical to test each condition 10 times. But in this case it is reasonable to assume the multiple tests at condition X will be representative of all tests(literature confirms this).

## RE: Small Sample Statistics

## RE: Small Sample Statistics

m777182