The result is restrictive fiscal targets, and this has led to a decline in public investment/GDP ratios in many countries (Roy et al. Some of the benefits a re more immediate, but many are evident only in the longer run.23 The time frame for generating measurable returns to this type of spending (and thus in many cases borrowing) may be as long as 5 to 10 years. By that time, appropriate public investments will have begun to expand the productive base of the economy, generating (taxable) incomes with which to pay down the debt. Such investments then are both fiscally sound and sustainable.