I’m reading Esther Duflo, Michael Kremer, and Jon Robinson’s AER paper on fertilizer use in Kenya.  Summarized by Chris Blattman here.  I’m looking for the gender dimension.  It’s hard to find and interpret.  They sampled ~450 men and ~450 women  (based on lists of parents of children in primary school).  They are not clear in their various papers, but it appears the idea was the project  (ICS staff) would “deal” with the respondent (in supplying fertilizer, seed, demonstrations, the SAFI savings commitment program to purchase fertilizer in advance).  So presumably, even if a man or woman wasn’t the farm manager, the project would deal with them (somehow I cannot see the ICS field staff refusing the speak to the male farmer and instead talking about fertilizer and farming with the shopkeeping wife…). Like I said, not clear in this or the various other papers I have seen online. Probably there is some project document that explains more clearly.

But that’s not the department of buried in a footnote point.  There are three footnotes actually.

One is fn 3: “For instance, consider a farmer with an hourly wage of $0.16 (the average wage rate for the area in Tavneet
K. Suri 2011) for whom round-trip travel to town to buy fertilizer takes 30 minutes and who can initially afford only 3.7 kgs of fertilizer at a cost of $1.92 (the average bought through the program described in this paper). Since the returns to half a teaspoon of top dressing fertilizer are 15.0–27.2 percent over a season (52–85 percent on an annualized basis), netting out the lost wages for time spent shopping for fertilizer would leave the farmer with a 48–81 percent annualized rate of return.”

And then later fn 9: “Most farmers who bought fertilizer through the SAFI program did not buy enough that they would have had to pay for transportation. On average, farmers who bought fertilizer through the SAFI program bought 3.7 kilograms of fertilizer (at a total cost of 135 Kenyan shillings, or $1.92), and only 1 percent of farmers bought more than 10 kilograms. It would take the average farmer roughly a half-hour to walk to town, buy fertilizer, and walk back. For a farmer who makes $0.16 per hour (as in Suri 2011), the SAFI program would save her a bit less than 5 percent of the cost of the fertilizer bought by the average farmer. This cost would be substantially smaller if the farmer were going to town anyway and so would not miss any work time.”

And then the money footnote 11: “Throughout this paper, we focus on usage of fertilizer rather than the quantity of fertilizer used because there is substantial underlying variation in the quantity used by farmers, which would make it difficult to pick up effects in average quantities. The standard deviation in kilograms of fertilizer used is 53, whereas farmers who bought fertilizer through the SAFI program bought only 3.7 kilograms, on average.”

What does this all mean?  Nowhere in the text of the paper does the reader have any idea that they are talking about $2.  That the annualized return of, say, 50% on this $2 investment is $1.  That in the sample of ~900 farmers, the variation in fertilizer quantities is hugely overwhelming the amounts on offer in the experiment.

(If 50% of farmers are using zero kg, and those who do buy have a uniform distribution in quantities, then the average level of fertilizer use must be on the order of 150kg to have a standard deviation of 53 kg.   A study of fertilizer prices in Kenya suggests that three 50kg sacks of fertilizer cost about $45.  100-150 kg is in line with what cotton farmers in Burkina Faso, just as poor as Kenyan farmers, purchase every year for their cotton farms.  See this good paper on nation-wide use of fertilizer in Kenya, suggesting indeed 100kg per hectare is the average.)

Page  2354 of the paper: “As discussed in detail in online Appendix Table 2, panel B, using one-half teaspoon of fertilizer per plant increases yield by about $25.22 per acre and costs $19.83 per acre.”  So the cost is about $20 for a hectare’s worth of fertilizer, about the price of a 50kg sack.  And the benefits are about $5.  But farmers were only spending $2 in the program.

Isn’t this 20-25% of $2 program then a kind of quite low stakes experiment (they normally spend $20 on fertilizer) where response bias could overwhelm incentives, especially in the context of the experiment being run by an NGO that is probably distributing benefits in the hundreds of dollars to each village in the form of schooling, water, not to mention the large team of researchers?   Maybe it is excellent practice to run low stakes experiments like this that can be scaled, but I wish the authors had been more modest about the claims.  (Because they suggest the results could usefully inform fertilizer policy expenditures in the hundreds of millions of dollars .)  And not bury an important fact in the footnotes.