We are only a year into the lifetimes of the Nintendo Wii and the Sony PlayStation 3. We can't know with certainty the final distribution of ESRB ratings on those platforms years in the future, but we can look back to last generation for some guidance. Specifically, did the ratings distributions for the GameCube, Xbox, and PlayStation 2 change from their first year of software to the final library of software?
For the period between October 2000 and December 2002, I have used the data available through MobyGames, which permits filtering of games by system, date, and ESRB rating. While MobyGames does not have an exhaustive record of all games for all three platforms measured here, its data for the period in question appears to be reasonably complete.
Below are the ratings for the games released on the PlayStation 2 between its launch and the end of 2001, approximately 14 months. Beside it, we've placed the graph of the distribution for all PlayStation 2 games to date, over seven years since the system launched.
If we combine the E and E10+ categories, the two graphs are very similar. That is, the distribution of ratings did not appear to change much in the time from October 2000 to November 2007.
The Nintendo GameCube during its first 13 months -- from November 2001 to December 2002 -- is also a reasonably good predictor of that platform's final distribution of ESRB ratings:
Again, combining the E and E10+ categories makes the two graphs look almost identical.
The Microsoft Xbox, shown below, is an exceptional case:
Notice that the prevalence of M-rated Xbox games grew significantly over the lifetime of the system. In fact, the prevalence of M-rated games on the Xbox grew from 11.7% of the library at the end of 2002 to 19.2% today. During that same period, the representation of T-rated games in the Xbox library diminished and the importance of E-rated games increased.
The increase in the importance of E-rated games at the end of the Xbox's market lifetime could be an indication that Microsoft's plan to reach out to a wider audience of gamers is not a recent development driven only by the rise of the Wii.
A game submitted to the ESRB for review is typically assigned a rating irrespective of whether that game reaches the market or not. For example, Payback by Destination Software for the Game Boy Advance was given an M rating but was never released in North America. (It was released in other regions, like the United Kingdom and Europe, where it was declared appropriate for gamers aged 12 years and older.)
Moreover, the ESRB database contains games which have received ratings and will be released in the near future. As of this writing (11 November 2007), the game Time Crisis 4 for the PlayStation 3 has been assigned a rating of T by the ESRB, the ESRB database reports this rating, and the game will be released in a matter of days. On the other side, the database does not report a rating for Uncharted: Drake's Fortune, another PlayStation 3 game which is on its way to stores now. [Ed. note: Both games have been released as of this writing. Uncharted eventually scored a Teen rating.]
For these reasons the ESRB database is not a perfect reflection of reality. However, the defects in the data are small relative to the total number of games. The ESRB database reports well over 1000 games for both the PlayStation 2 and the Game Boy Advance, which means each game represents less than one tenth of one percentage point.
On the other end, the PlayStation 3 has 176 games in the database, so a single game represents around six tenths of a percentage point. Nearly every feature of the distribution graphs discussed above represents three percentage points or more. Therefore what errors exist in the ESRB database will not greatly affect the contours of the graphs above.