Are the short-run and long-run concepts comparable? Answer: The short-run and the long-run concepts are not comparable because the ________ behind the short-run and long-run concepts are different. The short-run concept of diminishing marginal returns assumes that at least one of the inputs is fixed, on the other hand, economies and diseconomies of scale as well as returns to scale - the long-run concepts - assume that all the inputs are variable