The MPC provides six samples from the 1970 US Census (1% metro fm1, 1% metro fm2, 1% state fm1, 1% state fm2, 1% neigh fm1, and 1% neigh fm2).
Can I combine the six sample to obtain a 6% sample? - Assuming that I divide the sample weight by 6 (e.g., new_weight = perwt/6).
Within each form, the three samples were selected by an independent random draw with replacement. As a result, some cases could appear on both the Metro Form 1 and the State Form 1, for example. Some researchers choose to disregard this overlap due to the small number of cases and treat a combined 6% sample as if there are no duplicates.