Yield effects of tissue culture bananas in Kenya: accounting for selection bias and the role of complementary inputs

We analyse yield effects of tissue culture (TC) banana technology in the Kenyan
small farm sector, using recent survey data and an endogenous switching
regression approach. TC banana plantlets, which are free from pests and diseases,
have been introduced in East Africa since the late 1990s. Although field
experiments show significant yield advantages over traditional banana suckers, a
rigorous assessment of impacts in farmers’ fields is still outstanding. A comparison
of mean yield levels between TC adopters and non-adopters in our sample
shows no significant difference. However, we find evidence of negative selection
bias, indicating that farmers with lower than average yields are more likely to
adopt TC. Controlling for this bias results in a positive and significant TC net
yield gain of 7%. We also find that TC technology is more knowledge intensive
and more responsive to irrigation than traditional bananas. Simulations show
that improving access to irrigation could lift TC productivity gains to above
20%. The analytical approach developed and applied here and the finding of negative
selection bias may also be relevant for the evaluation of other agricultural
technologies.