Take N voters at random. Ask each of them their favorite party, and check to see how big that party is as a fraction of all voters. Take the average of those fractions. Take the reciprocal. Voila: an estimate of ENP. (If you want a better estimate, use a bigger N. But even N as low as 10 will get you a reasonable guess.)
Example: you choose 4 voters. 2 of them are from a party with 40%, one has 25%, one has 15%. Average is 30%, reciprocal is your estimate of ENP: 3.33.
Size of party counts twice: once explicitly, and once in the probability that a party will be sampled. So the formula is just one over the sum of party-size-squared. But I think my version gives a better feel for why it matters.
You can usually google up ENP estimates for most countries, both in terms of voters and in terms of parties in the legislature. The latter number is usually lower. It’s around 2 in the US and over 6 in Israel.
I keep running out of working memory trying to parse this sentence. :)
Take N voters at random. Ask each of them their favorite party, and check to see how big that party is as a fraction of all voters. Take the average of those fractions. Take the reciprocal. Voila: an estimate of ENP. (If you want a better estimate, use a bigger N. But even N as low as 10 will get you a reasonable guess.)
Example: you choose 4 voters. 2 of them are from a party with 40%, one has 25%, one has 15%. Average is 30%, reciprocal is your estimate of ENP: 3.33.
Size of party counts twice: once explicitly, and once in the probability that a party will be sampled. So the formula is just one over the sum of party-size-squared. But I think my version gives a better feel for why it matters.
You can usually google up ENP estimates for most countries, both in terms of voters and in terms of parties in the legislature. The latter number is usually lower. It’s around 2 in the US and over 6 in Israel.