1) Keep seasonality in mind – the sales of products and services may be prone to significant seasonal variations determined by people's actual needs, purchasing power, access and other factors. For example, sellers of agricultural inputs are likely to record very high sales in the months before (and during) the agricultural season but their income shrinks in the remaining months. This means that you need to:
- ensure that your baseline and endline data is collected at the same time of a year, otherwise you might be comparing two incomparable data sets (e.g. sales in the ‘high’ and ‘low’ season)
- if this is not possible, you will have to ask the respondent to recall the sales from a comparable period. However, such data is likely to be less accurate as the respondents might not correctly remember the amount of products they sold
2) Consider using a complementary indicator assessing the financial value of the products sold: “average sales generated by [specify the target groups] from selling [specify the product] in the past [specify the period]”. To calculate its value:
- for each seller, multiply the total number of products sold by the unit price it charges
- add up the individual sellers’ sales of the given product
- divide it by the number of surveyed sellers who sell the product
3) You can either measure average sales (for example, sales per month) or the total sales over a given period (or both).