The 1970 stats are just saying that of the 4% of people who held a degree, 20% had parents who also had a degree (the 20% is a subset of the 4%, the 2 numbers a

The 1970 stats are just saying that of the 4% of people who held a degree, 20% had parents who also had a degree (the 20% is a subset of the 4%, the 2 numbers are not directly comparable). This in fact means that graduates-with-degreed-parents were rarer than graduates without. This situation has changed when we look at 2020. The overall number of degree holders is still relatively low compared to overall population (14%) but of this number a full 2/3rds now have degreed parents. The situation within this group has reversed.