1. 1. In: Statistisch Jaarboek van PCGD/RPS (up to and including 1980)
2. 2. Maandstatistiek voor het Financiewezen (until October 1978) and Jaarboek van Amsterdam (up to and including 1978).
3. In conformity with Cramer’s (1978) approach, these might be estimated on the basis of totals recorded at the Banks’ Clearing Institution. In view of the large volume of unknown payments for 1977 — Cramer estimates them at nearly two-thirds of the Institution’s transactions — and the far-reaching assumptions which must be made, such an approach seems less suitable for the long sample period — especially because the Institution only started to operate during that period.