13.10 As a preliminary step in optimizing the coating process of iron oxide nanoparticles engineers explored the effects, of two factors each having two levels on the response y = increase in particle size (%). Factor Low level High Level Factor A molecular weight of chitosan low high Factor B concentration ratio of chitosan-TPP 2:1 6:1 Given the following observations (Source: Replicate 1 extracted from the design in S. Honary et al. (2013), International Nano Letters, 3(48). doi:10.1186/2228-5326-3-48): x1 x2 Rep. 1 Rep. 2 −1 −1 96.0 90.8 1 −1 91.0 93.6 −1 1 76.0 88.4 1 1 223.8 214.2

(a) Attach the sample means at the corners of a square. Comment on any obvious pattern.

(b) Obtain the point estimates of the effects and 95% confidence intervals.