Offense
Bourque scored 1,579 points in 1,612 games (0.98 ppg). Lidstrom scored 1,108 points in 1,494 games (0.74 ppg). I am excluding the current season (which works to Lidstrom’s advantage, as this would drag down his per game average). Clearly, Bourque played during a higher-scoring era and this needs to be taken into account, or else we’re being biased in favour of Bourque.
Bourque played from 1980 to 2001. According to hockey-reference.com, there was an average of 6.66 goals per game during those seasons. (I’m using a simple, rather than weighted average, as the difference can’t be material). Lidstrom played from 1992 to 2011 (again, excluding 2012). According to hockey-reference.com, there was an average of 5.57 goals per game during those seasons. Thus, Bourque played during an era that featured 19.52% more offense per game.
Adjusted for era, Bourque scored 0.98 ppg / 1.1952 = 0.82 ppg. Thus, after taking era into account, Bourque outscored Lidstrom by 10.5% on a per-game basis.
Defense
In those 1,612 games, Bourque was on the ice for 2,144 total goals against and 687 PP goals against. Thus he was on the ice for 1,457 even-strength goals against. I’m assuming for both players that the number of SH goals against (i.e. number of goals against they allowed while their team was on the powerplay) is minimal. Thus, Bourque was on the ice for 0.90 ES goals against per game.
In his 1,494 games, Lidstrom was on the ice for 1,658 total goals against and 520 PP goals against. Thus he was on the ice for 1,138 even-strength goals against. Thus, Lidstrom was on the ice for 0.76 ES goals against per game. Clearly, Lidstrom played during a lower-scoring era and this needs to be taken into account, or else we’re being biased in favour of Lidstrom.
Adjusted for era, Bourque was on the ice for 0.90 esga/g / 1.1952 = 0.76 even-strength goals against per game. Thus, after taking era into account, Bourque was on the ice for 0.7% fewer ES goals against per game.
We can do the same analysis for the penalty kill. Using the numbers from above, Bourque was on the ice for 0.43 PP goals against per game. Lidstrom was on the ice for 0.35 PP goals against per game. Adjusting for era in the same way done before, Bourque is on the ice for 0.36 PP goals against per game. Thus, after taking era into account, Lidstrom is on the ice for 2.4% fewer PP goals against per game.
If we assume that two-thirds of all goals against are at even-strength and one-third are on the penalty kill, then Lidstrom is on the ice for approximately 0.3% fewer goals against per game.
Overall
Bourque is approximately 10.5% better offensively, and Lidstrom is approximately 0.3% better defensively. Therefore I’m comfortable saying that, on a per-game basis, Bourque was about 10% better than Lidstrom. Also, Bourque maintained his strong level of play over a longer period of time.
Playoffs – somebody calculated that, adjusted for era, Lidstrom was equal to Bourque in playoff scoring (I don’t have the link, but it sounds reasonable to me). Assuming that their relative level of defensive play stayed about the same, they were probably even on a per-game basis in the playoffs. Lidstrom should get credit for maintaining this high level of play over a longer period of time.
Taking everything into account, on a per-game basis Bourque is superior in the regular season, by a small but clear margin. On a per-game basis they’re virtually even in the playoffs. It’s close, but Bourque is the better player.