In Reply to Parent Post by Miner
Take a look at the attached analysis. Ask any specific questions that you may have, and I will respond.
The biggest concern that I would haveover this data is that you would expect the data to fall on either side of a 45 degree line. The Orthogal regression equation should be close to B = A. In this case the slope of the line is close to 1.3 instead of 0. There is also an overall bias greater than -2 for the means. Now, the 2-sample t and the test for equal variances both indicate that this is not significant, and that is true FOR THE RANGE OF VALUES STUDIED. If you exceed this range, there is every indication that it will become significant.
I checked the file attached and I have some questions:
1) Using the regression orthogonal, we have the equation B = - 2.854 + 1.280*A. In order to consider that the two instruments (A and B) measure the same thing, the slope must be 1 and the constant 0, instead of 1.280 and -2.854, respectively.
Since these conditions are not met, can I conclude that the instruments A and B do not measure the variability equally. Right ?
2) Using the test for "2 Variances", this shows that there is no significant difference between the devices A and B, contrary to what was stated with regression orthogonal test in item #1.
Can I conclude that the test "2 Variances" does not show the reality and that the variability of instruments A and B are really different ?
3) To make the orthogonal regression analysis you used the "Error Variance Ratio" (B/A) equals to 1.
How did you come to that conclusion/valor ?