The text on a Twix wrapper runs in the same direction as the Twix inside, so it’s better to say they’re top and bottom Twix - otherwise it’s ambiguous based on the direction of the packaging.
Also, for double blind experimentation, she shouldn’t know whether it’s a left or a right.
1970 was during the cultural revolution. In that year, the world population was 3.68 billion, and the population if China was just shy of 830 million - China had 22% of the world’s population, so if they held (only) 20% of the world’s prisoners, they’d have a lower than average incarceration rate.
The same is not true for the US today, we have less than 5% of the world’s population today.