In other words, Thornton may not decline in the next few years because he isn't part of the subject group, or he may decline just like them. So, how does one sit there and realistically determine whether or not they acquire a 35 year old? Give him a physical? OK, he's in good health. Look at how he's held up the last few years? Very durable, often playing 82 games, which, of course, can be a negative because it's more wear and tear, or it's a positive because he's just durable. How has his numbers been? Actually on the increase, not the decrease. Whatever that would mean.
I don't sit here and try to pretend I can predict when a player will begin his decline. It's like treating diseases. You do your studies. Double-blinded, randomized, and all that jazz. You do your statistics, you get a p value, and administer based on that. Of course you cannot 100% predict the outcome because that patient was not part of the control group of the study, and it was only effective in 72% of the patients, but at the end of the day you still need to choose a course of action because standing still...well, that's not a real option. So, you do the best you can to get data that is relevant and make your decision. Same with Thornton. We know players decline at a certain age. Some players may actually do better in their mid-30s, then decline, but by and large it's a decline. Ok. But how much and what can he bring today, next season and the season after compared to what you're giving up, and what can replace what's being given up, and is it worth it and affordable. Not all 35 year olds are going to decline from 76 points to 50 points in one season.