I've kind of got Traveller on my mind now. I was looking in the encounter tables and saw that encountered police are always armed with revolvers. I know that while many police departments use revolvers, many also use automatics, and then that got me to thinking that in some places and in certain circumstances, the police also use shotguns, submachine guns, and assault rifles, and there's really no reason that future cops in similar circumstances wouldn't use advanced combat rifles or some of the other higher tech level weapons in the game. The most basic constraint on what the department uses is going to be its budget, and that is going to depend on how many taxpayers they have paying in and how much they pay in taxes. So now I have to figure out some basic economics here.
There are listings for salaries of starship crew, and Mercenary has wages for all ranks of mercenary forces, but the best, most general indicator of the income of regular people in the Traveller game is the listing of food and lodging costs. We can take the "starvation diet" and "dismal lodging" as the bare minimum you can pay without becoming homeless and hungry, and the "excellent" levels of food and lodging as the upper limit of actual quality increases, as opposed to conspicuous consumption. This leaves two in-between levels of apparent middle class costs.
Now, if you've studied statistics at all, you should know the difference between median and mean. The median is what you get when you line up all your data points in order and find the one in the middle. For incomes, the median is the point where half the population makes less and half makes more. Mean is what you get when you add up all the incomes and divide by the population...per capita income, in other words. When you're talking about incomes, the median will almost always be less than the mean, and will never be more. This is pretty obvious if you think about it: the half of the population that makes more than the median income drives up the mean, and while the half making less than median income pulls it down, there's a lower limit to how low they can go and survive, whereas no one's survival is impacted by having too much money. I propose we take the "reasonable diet" and "acceptable lodging" as the median, with the "good" levels as the mean.
Since we know how much is spent on food and lodging per capita, we can ballpark the total income. In 1977, consumers (Americans at least) spent 25% of their income on food and 33% on housing. Since "good" food and lodging both cost 200 Credits per month, we can see this doesn't map exactly. To be honest, I'm not too surprised that Marc Miller didn't bother getting that far into the weeds on this, but I'm going to go with it anyway; he surely had some impression of how the economy was supposed to work just from living in it. And I'm specifically using 1977, because using current costs would end up looking more like cyberpunk. So, if 400 Cr/month is about 58% of the total income, then the total should be about 690 Cr...let's just call that 700 Cr/month as the mean. For what it's worth, the median income (closer to what the average man on the street would be making) is just over 500.
I originally was going to work out an income distribution chart or something, to figure out how many people we had on any given planet or any given sector of space living in poverty, and how many living just above poverty, and so on, and then work out the size of the economy, but then I realized that since I already have the mean (per capita) income, I just need to multiply that by the number of people to get a GDP for that particular political division.
So, a planet with 10,000 people on it would have a monthly GDP of 7 million Credits, and if we assume that police departments take up 1% of GDP (which is about what they did in 1977), this planet's police would have a monthly budget of 70,000 Credits for salaries and equipment. If they're paying their officers the mean income (and police do tend to make more than the median income), they could have somewhat less than 100 officers, depending exactly on what their costs are for equipment procurement and maintenance. I'll give some more thought to what kind of costs that will entail and post about it later.