1) Farmers often do not report the crops which they planted but due to crop failure or other circumstances did not harvest. Consider therefore adding an extra question: Were there any crops which your household planted but did not harvest due to poor weather, pests or other reasons? Depending on the purpose of your survey, decide whether these crops should be included or not.
2) Many different varieties of crops are grown (for example, there are over 50 varieties of maize). If you need to know what they are, assess them as a part of the survey.
3) If your main interest is assessing the proportion of farmers who diversified their crop production, consider using a slightly different indicator: “% of targeted farmers who increased the number of crop types grown in their farm”. However, be aware that such an indicator requires collecting baseline and endline from exactly the same respondents which is not easy (the baseline sample size also needs to be larger, so that even if some farmers are not available for the endline, the sample still maintains its representative size).
4) The data collected for the Farm Diversity Score indicator allows you to also assess the percentage of farmers growing specific types of crops.
5) Many households’ diets depend on collecting wild foods. If you are interested in households’ physical access to food, you might want to include additional questions assessing households’ use of local wild crops (while keeping in mind that they should not be counted as “farm production”).
6) Keep in mind that many farmers practice crop rotation. Therefore, if you want to also use the farm diversity data for assessing the number of farmers experienced in growing a particular crop, add an additional question for frequently rotated crops: Are there any crops which you regularly grow but due to crop rotation you did not plant them in the [specify the season your survey assesses]?
7) If possible, measure crop diversity at least one season after you completed your crop production support, otherwise you won’t see whether farmers continue growing the promoted crops in the absence of external assistance.
8) Ensure that the data collectors always interview the household member primarily responsible for crop production (not any other person). If the person is not available, interview another household and return later.
9) If required, you can extend the questionnaire and also include the domestic animals (possibly also their number).
10) If you have a clear use of such data, consider also assessing the use of the grown crops (primarily for sale / for consumption / both) and the cropping area per each crop.
11) European Commission's DEVCO recommends using a similar indicator: "Crop diversification index".