What is a good sample size for determining whether dice are truly random?
April 30, 2008 11:41 AM Subscribe
How many times would I have to roll a standard 6-sided die to get a statistically representative view of whether it was truly random or not?
I have a bunch of dice that I haven't used in years. The other day, I was playing with one, and I noticed that the 5 came up fairly often. I started rolling the die and writing down the results, to see if it was just a short term statistical fluke, or observer bias, or if the die really favored the 5.
I think I ended up rolling it around 200 times, and 5 definitely had a significant edge.
Now, I'd like to check my other dice. However, I'm not a statistician. I understand that, obviously, the larger your data set (the more times you roll each die and write down the results), the better your analysis of non-randomness will be. However, I know that it isn't necessary to roll the die 1 billion times to check for randomness, that there is some generally accepted statistical minimum, below which the margin of error is too large, and above which the margin of error is generally considered acceptable.
How many die rolls is that point?