It was 5 minutes' work to scan through the episode list on Wikipedia, which conveniently lists each episode's guest players. I made a little spreadsheet, sorting the players per episode by apparent gender (which at this distance looks like simply Boys and Girls; a more thorough analysis might split those numbers up further). And that very rushed spreadsheet yielded this graph of gender representation per episode:
|Click to embiggen.|
Note that the host, Wil Wheaton, is counted as a player in all of these episodes, giving an automatic +1 to the boys (hence the solid blue bottom of the graph); more on this below. Note also that series co-creator Felicia Day also steps in as a guest player occasionally, and I've marked all of her appearances with the symbol F. The standard show format features Wil plus three guest players, and exceptions to this are rare (about once per season). Two-parter episodes come up once or twice per season, but I've counted each of these as two separate episodes here. If the point is to test representation, then getting twice as many appearances as in a single episode should be counted as such.
So, what does it mean? To draw some useful conclusions from the constantly shifting graph, I've drawn out three things:
1. The average number of boys and girls per season. (Includes Wil Wheaton.)
2. The average number of non-Wil Wheaton boys per season.
3. The number of episodes per season that have an exact 50/50 gender split. (Includes Wil Wheaton.)
It would be fruitless to look for the 50/50 gender split without including Wil Wheaton, because of the standard four-player format.
I definitely wasn't crazy to notice a shift away from women guests in the early part of season 4. Episode 4-3 is a brief exception, and then there's a string of mostly-men episodes for a while. But the good news is, season 4 over all is much better.
The Wil-inclusive average gender split for each season is:
S1: 2,9 boys, 1,2 girls
S2: 2,6 boys, 1,5 girls
S3: 2,5 boys, 1,5 girls
S4: 2,5 boys, 1,6 girls
Which looks like it's tending towards equality.
It's even clearer with the Wil-exclusive average gender split per season:
S1: 1,9 boys, 1,2 girls
S2: 1,6 boys, 1,5 girls
S3: 1,5 boys, 1,5 girls
S4: 1,5 boys, 1,6 girls
Unsurprisingly, the boys lose their +1, and viewed this way, only season 1 is particularly unequal.
There are arguments in favour of either including or excluding Wil Wheaton from our count. But either way, the trend is headed in the same direction.
And finally, the number of perfectly equal episodes per season are also tending upwards:
S1: 5 episodes
S2: 7 episodes
S3: 9 episodes
S4: 11 episodes
I have no idea if this is intentional on their part or not, but at least it satisfies my initial concern. Things look sane and reasonable.
One final observation: Appearances by Felica Day seem to be less common over time. That's a pity, because I always enjoy her participation, but I suppose this means they're finding it easier to find new people to fill out their casts.