We originally made Custom Bingo with small groups of children at a birthday party in mind. The original game had a 3x3 card using themed images. Since then we have added a 4x4 picture bingo card and a 5x5 picture bingo card as well as a traditional bingo card. One thing we have found is that picture bingo tends to have a lot of winners at the same time when playing in large groups. The reason is that we only have a pool of 30 images to choose from (see below) as opposed to the 75 numbers that traditional bingo uses. So here are some suggestions if you need to reduce the number of winners at the same time:
If you have a group of 30 or more:
If you have a group of 15 to 30:
If you have a group of less than 15:
I don't want to pretend that I am a mathematician or statistician but the reason that our bingo does not work that well in large groups has to do with the probabilities of a winner given that there are only 30 images in the 'pool' for our picture bingo.
Granted there are thousands of combinations (possible playing cards) when you are choosing 24 images out of a pool of 30 to create a 5x5 bingo card. (25 spaces less one free space.) The problem is not with the number of possible cards but rather the size of the call sheet or pool of pcitures that you choose from when playing the game.
If you are playing blackout bingo with a 5x5 picture bingo card the probability of a having a winner after calling 23 pictures is zero. You can't have blackout bingo (24 spaces) with only 23 pictures called. At this point there are only 7 pictures left and chances are roughly one in seven that a player will have a blackout after the 24th picture is called. That means that if you have a group of 30 people you are likely to have around four players call bingo after the 24th picture is called.
Having 4 people call bingo at the same time might not be a problem if you have a classroom of 7 year olds all playing for a Halloween treat. When Leanne played bingo with her Sparks group they continued playing until all the girls had called bingo and everyone got a treat. It worked perfect because all the girls had BINGO'd once the 30 pictures had been called.
If you have a group of 30 adults competing for a door prize it might make it a little awkward trying to split the prize four ways.
I have oversimplified the probability analysis as any mathematician would tell you but I think you get the gist of it. In order to reduce the odds of people calling bingo at the same time you need to increase the ratio of call out pictures to the size of the playing card. If you play 5x5 picture bingo the ratio is 30:24. If you play 3x3 picture bingo the ratio is 30:8 and that means when the eighth picture is called there is a 1 in 23 chance that you will have a winner.
For large groups you can increase the pool by playing traditional number bingo (75:24) or by playing 5x5 picture bingo combining two themes (60:24).
Hope that makes sense. I have to stop now...combinations, permutations, probabilities and statistics give me a headache! (*grin*)