Group checks depend too much on whether you have an odd or even number of players - here's a proposed fix
In DnD 5e, a group check is a helpful mechanic to approach situations where the entire party succeeds or fails together. While group checks don’t always come up in the average session, they certainly have their place. In my games, I often use a group Stealth check if the party tries to collectively sneak past an enemy or to adjudicate a Survival check to see if they navigate a hazardous terrain effectively.
Unfortunately — perhaps due to the designers assuming they are rare — the rule determining group checks is very sensitive to whether you have an odd or even number of party members.
Let’s take a look at the rule as written:
To make a group ability check, everyone in the group makes the ability check. If at least half the group succeeds, the whole group succeeds. Otherwise, the group fails. — Player’s Handbook p. 175
The rule itself is simple, but issues arise in the: “at least half the group” clause. As we know, party sizes in DnD are typically somewhere between 3-6 players. If you happen to have an odd number of players in your group, you’re stuck with interpreting what that “at least half” means — do you round up or down?
That decision is best left to the rules lawyers. Instead we focus on the fact that either decision leads to a situation where your party is punished or rewarded just because they have an odd number of members.
The below figure shows what I’m talking about. (Here I assume each party member has a 50% chance of success, which is not necessarily realistic but doesn’t change the result).
Every time you hit an odd numbered group size, the success chance shoots up or down compared to an even sized party, with the direction being determined by how you round. These are the sorts of odd results you end up with when you take a simple rule and combine it with having to round small numbers.
A modification of the rule can alleviate this issue. I propose the following change to the rule as written:
To make a group ability check, everyone in the group makes the ability check. If the group has an even number of members, the whole group succeeds if at least half the group succeeds. Otherwise, the group fails.
If the group has an odd number of members, the DM rolls a dice and records if the result is odd or even. If the DM rolls odd, the whole group succeeds if at least half the group succeeds, rounded down. If the DM rolls even, the whole group succeeds if at least half the group succeeds, rounded up. Otherwise the group fails.
Essentially, we change the rule so that with an odd number of players, the DM randomly chooses between rounding up or down the number of players required for success. This randomization process results in a compromise between the two extremes.
The below figure shows how the proposed rule compares to the original:
The success chance of our new rule is shown in red. It is clearly more well behaved when it comes to odd numbered group sizes. I’d go so far to argue that the proposed rule is more fair to the players — no group should be significantly affected by whether they have an odd or even number of members!
The downside of the proposed rule is that it places a little more burden on the DM by requiring an extra roll, but I believe the added complexity is worth it. Maybe I am the only DM who uses group checks and it doesn’t really matter, but hey, hopefully there was something interesting here to think about.