Non-destructive evaluation (NDE) is a method used to describe the properties of components or materials without causing any permanent physical change to the units. It includes the determination of properties of materials and the classification of flaws by size, shape, type and location. This method is most effective for detecting surface flaws and characterising surface properties of electrically conductive materials. Assume that data were collected that classified each component as being unflawed (Type 0) or having a flaw (Type 1) based on manual inspection and operator judgment. The size of the crack in the material was also reported. Do the components classified as unflawed have a smaller mean crack size than components classified as flawed? The results in terms of crack size in millimetres are in the data file < CRACK >.

a. Assuming that the population variances are equal, is there evidence that the mean crack size is smaller for the unflawed specimens than for the flawed specimens?

(Use α = 0.05.)

b. Repeat

(a) assuming that the population variances are not equal.

c. Compare the results of

(a) and (b).