Population growth rate

[Tisifoni12]

Just thought I'd look up population growth rate for comparison with Stellaris' base rate of 3%. The only technologically advanced dominant species for which we have any data is us.

Current human population growth rate is 1.1% . . .

I'm not saying that the growth rate should be re-set to 1%, but I think there's some scope for:

• allowing players to lower the base rate
• edicts that encourage 'family planning'
• allowing players to, at species design, perhaps trade life expectancy for fertility (the insectoid Skrykt reproduce prolifically but only live 15 years)
• population growth is determined by birth rates and death rates; improved health and life expectancy in our experience tend to result in families choosing to have fewer children
• an authoritarian species might faced with a population problem choose to euthenise those over a certain age, or who are least able to contribute to the species' objectives

The standard base rate with few modifiers, and other than 'slow breeders' all modifiers adding to population growth rate, seems a bit narrow and gamey.

This is all of course further complicated by migration and by Stellaris apparently boosting the numbers of minority populations.

 

[Blurb]

Just thought I'd look up population growth rate for comparison with Stellaris' base rate of 3%. The only technologically advanced dominant species for which we have any data is us.

Current human population growth rate is 1.1% . . .

The current base pop growth rate in stellaris is not 3% - it is 3 pop growth per month.
No, these two things are not the same.

 

[Omnipax]

Current human population growth rate is 1.1%

Considering this means the population increases by 1.1% per year, the monthly growth rate would be:

(1 + x)^12 = 1.011
x = 1.011^(1/12) - 1 = ~0.000912 or 0.0912% growth per month

Representing this in Stellaris terms would mean you would gain 0.0912 growth points per pop per month on the planet.

So a homeworld starting the game with 24 pops would start with a growth rate of 24 * 0.0912 = 2.19 growth points per month, adding up to 26.28 growth points per year. This would mean it would take 3 years and 9-10 months to grow the first pop, depending on how things get rounded.

A homeworld instead starting with 28 pops (i.e., a Megacorp) would start with a growth rate of 28 * 0.0912 = 2.55 growth points per month.

Seems like Stellaris is surprisingly close to real life population growth rates, although Stellaris pop growth rate is linear instead of exponential (i.e., it does not depend on the number of already existing pops on the planet).

 

[Tisifoni12]

The current base pop growth rate in Stellaris is not 3% - it is 3 pop growth per month.
No, these two things are not the same.

True !
And below some informative maths which of course disproves my initial assumption.
It doesn't however mean there isn't still scope for finding ways to effect population further through life span, life expectancy, edicts and policies.

I looked at some saves for a recent game. Humans and at roughly generational intervals (taking a generation as around 25 years):

• 2200 : 24
• 2222 : 35 (4 worlds) AGRPA = 1.59
• 2257 : 69 (5 worlds) AGRPA = 0.97
• 2276 : 99 (5 worlds) AGRPA = 1.57
• 2292 : 126 (5 worlds) AGRPA = 1.5

Or 2200 - 2292 for a growth from 24 pop to 126 pop AGRPA is 1.1%

AGRPA = Average Growth Rate Per Annum

 

[Omnipax]

• 2200 : 24
• 2222 : 35 (4 worlds) AGRPA = 1.59
• 2257 : 69 (5 worlds) AGRPA = 0.97
• 2276 : 99 (5 worlds) AGRPA = 1.57
• 2292 : 126 (5 worlds) AGRPA = 1.5

Going from 24 to 126 within a span of 92 years would make the growth rate:

24 * (1 + x)^92 = 126
x = (126/24)^(1/92) - 1 = 0.01819 or 1.819% growth per year

That's reasonably high, but there are countries on Earth today with higher growth rates than 1.8%.

 

[Tisifoni12]

That's reasonably high, but there are countries on Earth today with higher growth rates than 1.8%.

There are also countries with declining populations; Japan, Russia
Some of your planets will have relatively high growth rates, your home world may, through migration see it's growth rate drop dramatically.

I think the core of my concern is that population growth can be enhanced by design (fast breeders), by tech/s, effectively by colonising more planets and I suspect there may be something else I've missed, the only reduction factor is the (slow breeders) design option.

 

[Tisifoni12]

Have just looked at an incomplete game with my slow breeding humanoid species (proxy Vulcans). 2200 pop of 24, 2300 pop of 119 across 6 worlds.
If I could do the equation Omnipax for comparison I would, but ^ is beyond my maths knowledge (and I have been googling . . .)

 

[MechaThumper]

Have just looked at an incomplete game with my slow breeding humanoid species (proxy Vulcans). 2200 pop of 24, 2300 pop of 119 across 6 worlds.
If I could do the equation Omnipax for comparison I would, but ^ is beyond my maths knowledge (and I have been googling . . .)

STARTING POPS x ( 1 + X ) ^ YEARS ELAPSED = ENDING POPS

so

24 x (1+X) ^ 100 = 119
or
-1 + (119 / 24) ^ (1/100) = X

X = 1.614%

 

[Tisifoni12]

Thank you !
Still no clue what the ^ means mathematically and therefore how the equation works . . .

 

[MechaThumper]

means to the power of, or exponent. it's shorthand for a repeating multiplier, so for example in 2 ^ 3 means 2 x 2 x 2.

( 1 + X ) ^ 100 means ( 1 + X ) x ( 1 + X ) x ( 1 + X ) x ( 1 + X ) x ( 1 + X ) for 100 times.