varieties and two levels of fertilizer (0 and 30 kg N/ha)
was used. All maize was intercropped with cowpeas and
sunflowers, a common practice in the area. Maize
varieties tested were the "local" flint variety and CCA,
an improved semi-flint composite. The data for the
Phalombe Project area are in Table VII-3.
 Data for each fertilizer level and for each variety
are fit by simple linear regression. This can be
accomplished easily on simple, pre-programmed electronic
calculators.
 The calculations for simple linear regression for
non-programmed calculators follow, based on using local
maize without fertilizer (LM) as an example. The values
of Yi are the individual farm yields for LM, or 2.2, 2.2,
1.9,..., 0.6. The values of e in the equation are the
mean yields for each farm, or 3.6, 3.2, 3.3, ..., 0.5. By
convention, X is used for e in the following.

 Ex2 = EX2 [(EX)2 / n]
 = (3.6)2 + (3.2)2 +...+ (0.5)2 [(27.6)2 / 14]
 = 65.02 54.41
 = 10.61

 Exy = EXY (ZXEY / n)
 = (3.6 x 2.2) + (3.2 x 2.2) +...+ (0.5 x 0.6)
 [(27.6)(18.9) / 14]
 = 42.68 37.26
 = 5.42


 b = Zxy / Ex2
 = 5.42 / 10.61
 = 0.511
and
 a = Y bX
 = 1.35 0.511(1.97)
 = 0.34

To estimate R2 it is necessary to calculate Zy2:

 Ey2 = Zy2 [(Yy)2 / n]
 = (2.2)2 + (2.2)2 +...+ (0.6)2 [(18.9) / 14]
 = 29.41 25.52
 = 3.89