# Help developing a scoring system for a tech tree based game

I'm working on a tech tree based project in which the player would select "advancements" to effect several measurement stats, or "basic stats". I have a working excel model that will calculate the "scores" for these basic stats based on advancements selected, but I'd eventually like to use these measurement stats that I have to calculate higher level measurements like population or total production power.

For example in the case of calculating "Population", I'd like to take the (current pop + (current pop. * fertility rate)) - death rate. Fertility rate would be calculated based on the "basic stats" of "health" and "food supply", and death rate on metrics like "health" and "squalor".

I'm not really sure how to use these measurements though... If health and food supply both start at 0 and increased by 5 over the course of a few turns, how should I use these scores in a meaningful way to do what I'm trying to do in the case of fertility rate? Fertility rate should be expressed as a certain percentage of total pop. but I'm not sure how to get there from two scores of 5. I don't think this will be a simple process, but I feel like I'm missing some basic concepts to put this into place. Is there a name for this kind of scoring system?

Any ideas would be appreciated! Thanks.

For your Population example, you are probably looking for a 'population model'. If you have interacting species, try something like the 'predator-prey' mathematical model:

(Wikipedia)

I believe a simpler model like the 'Logistic growth equation' (also see link on population models) is a simplification of these equations.

A general technique for taking several numbers and producing a single number from them when you don't know the precise relationship between them is a weighted sum.

Basically you select floating point weights for each score then multiply the current value of each state by its weight and sum that up to get your result.

So for your example you could use this formula:

fertility_rate = health * HEALTH_WEIGHT + food * FOOD_WEIGHT + squalor * SQUALOR_WEIGHT;

where HEALTH_WEIGHT, FOOD_WEIGHT and SQUALOR_WEIGHT are constants that you can tweak to get the effect you want.