I am reading a paper which empirically tests if primary exports affect education attainment in LAC countries over the period 1965 to 2010. It uses percentage of secondary school enrollment as dependent variable. It mentions that data has been obtained from Barro and Lee (2013). But the problem is that Barro and Lee provide data for every 5 years interval where as the data on primary exports is available on yearly basis. So I'm confused as to how can one perform the regression when the data on one of the variables are largely missing? I'm using stata to perform the task.