An experiment described by M. G. Natrella in the National Bureau of Standards€™ Handbook of Experimental Statistics (1963, No. 91) involves flame-testing fabrics after applying fire-retardant treatments. The four factors considered are type of fabric (A), type of fire-retardant treatment (B), laundering condition (C€”the low level is no laundering, the high level is after one laundering), and method of conducting the flame test (D). All factors are run at two levels, and the response variable is the inches of fabric burned on a standard size test sample.

The data are:

(a) Estimate the effects and prepare a normal plot of the effects.

(b) Construct an analysis of variance table based on the model tentatively identified in part (a).

(c) Construct a normal probability plot of the residuals and comment on the results.

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= 40 30 (1) 42 = 31 45 ad bd abd 50 = 29 39 ab = 40 cd 28 46 32 25 acd bcd ac 50 23 abc abcd