Wow! That article is even older than me.
I found this statement in the article most interesting:
I had never seen actual numbers for this effect. Unfortunately, it's not clear whether it was an increase of 2.5% points above the bagged measurement (e.g. 3% in bagged implied 5.5% in topped), or was 1.025 times the bagged value (e.g. 3% in bagged implied 3.075% in topped).Topping has a major influence on building up nicotine, and, from
records over a 5-year period, it was found that topped plants had, on an
average, an absolute increase of about 2.5 percent alkaloid as compared
with bagged ones. An increase of 2 percent would be a conservative
estimate of the effect of topping....
Bob