Table 2.

Design Efficiency Statistics.

No. of questions	Sample size	Main effects standard error	Interactions standard error	D-efficiency
6	320	0.042	0.050	695
7	280	0.041	0.050	703
8	240	0.041	0.050	695
9	210	0.041	0.049	689
12	160	0.042	0.048	699
13	150	0.040	0.048	705