An alternative to the GC-ECD method for determining dioxines, mentioned in one of the previous questions, is GC-MS. The two methods are compared by measuring the same set of 8 samples in triplicate. The mean values are plotted below.

The intercept of the best line through the points is -2.9, with an s.d. of 3.2, and the slope is 1.3 with an s.d. of 0.3. Which of the following statements is correct?

We cannot detect a difference between the two methods.
The methods do not give the same results because the points are not near the dashed line.
The methods do not give the same results because the intercept is not equal to 0.
The methods do not give the same results because the slope is not equal to 1.