Originally, the ratings were going to serve two purposes. One was to even the field across all eras so that we don't have the differences in the game affecting who plays well in the sim. The other was to introduce created players (i.e. rookies) like Baseball and Hockey have, but after looking at how that would affect the game, we decided to stick with historical players.
When we introduced the 60s teams into the mix, it was obvious that the stats, especially for passing, were going to cause some issues with the engine. Since the passing game was mostly longer passes than today, it meant lower completions and higher INTs. So 60s QBs were quite worthless in SimLeagues. On the other hand, the 60s Defenses were quite strong. You can even see some differences across the 70s and 80s. Running games were pretty much the same with a few bumps here and there.
Anyway, we decided to go with ratings as a tool to compare football across the decades. We figured this would be easy to use in the engine as well as easy for users to compare the players. The higher the rating the better.
How did we calculate the ratings? Well, we certainly didn't go through the thousands of players and set them manually. We looked at the distribution of stats for certain players for each season, finding an average performance and the spread of bad to good. From this we rated the average players with average stats at 50 and calculated ratings for the other players based on the stats for that season. The average and spread was kept fairly close from season to season, but there are some cases where there was a hard shift in the stats, either from rules or the game changing.
Anyway, what we wanted was to keep the top players from the 60s, 70s, and 80s comparable to the players of today. What If Johnny U. played for the '95 49ers? Well, his completion percentage would be better and his yds/completion would not be as high. Also for receivers, they didn't have quite as many catches, simply because there weren't as many completions, so we also wanted to allow them a fair shot at performing in today's game. Amazingly, the running game is pretty much the same from the 60s to today, so the ratings are fairly close to comparing hard stats. But it was much different when we start looking in the 40s and 50s, so we might break from that when we introduce those players. The same thing goes for the Defenses. Arguably the top historical defenses were not the top defenses in the sim.
One quick thing about the passing ratings. In the new ratings we take into account completion percentage combined with yds/comp. Before it was just comp %, which did not take into account more aggressive passing games. The assumption is that a high %/ low ydg QB may be the same as a low %/ high ydg QB if they played the same type of game. Of course, there may be exceptions to this rule, but for the most part it works.
FG and punting ratings were a little different than the "50 = average" rules. Punting is straight up comparison of yds/punt, so there is no difference between 45 yds/punt in 1960 or 2000. FG ratings are similar in that they are not adjusted across seasons, but they are different than the old way of breaking out the different FGM % into ranges. The FGM for the 50+ really could not be used straight up. You had 100% guys that may have made a couple 50+ FGs and now that would mean they would make every one? You also have kickers that were like 66%, which was basically 2 out of 3 kicks. There were also some weird %s in the middle ranges if someone had few kicks for that range. The kick ratings provide a more consistent performance.
Well, that's a lot about the ratings. If there are any more questions, I'll be glad to answer them.