LAE – Census data in Papua New Guinea have always been considered less a reflection of ground truth and more a best approximation based on available reported figures from household interviews.
(Rule of Thumb: Always have the salt handy.)
Rather than arguing theoretical knowledge, I'll make an educated guestimate of what's likely in terms of rural population growth rates.
These are based on recent observations, which I hope may be disproved (or my math and stats totally destroyed by more astute and learned commentators).
Often desktop studies are scoffed at even when they are designed to be carefully adjusted within error bounds: a fact to which most honest statisticians, economists and geographers will attest.
Even a rudimentary exercise shows the potential for growth in our highly fecund population.
If families have three kids, I guess the child-bearing women probably had about five or six pregnancies during their productive years.
As a national average for household sizes the number seven (i.e., strictly PNG’s 'nuclear family') has been a consistent finding on a number of recent baseline surveys that my teams have conducted for project work.
Last month I asked a focus group (n=25) of young couple families to describe what a common household size would be in that part (two urban-village communities) of the Rai Coast.
The surprisingly unanimously agreed answer was 'mama, papa na faivpela pikinini'.
That may be circumstantial evidence but it does fit with National Statistics Office estimates from Census 2011 as the national average household size.
Suppose, in say 15 years (2037), those 25 families have seven members each, that's 175 people.
At a gender balance of about two males to three females, say that three females from each household started their own families at around 15+ years age, not unusual in PNG rural scenarios.
Then after another 10 years (2047) we have 75 new households with five new members each, a total of 375 more humans 25 years from now.
Maybe five years after them the male youth catch up with their sisters and start their own families (generally males mate later). That's another 50 new households with maybe five new members each. Another 250 in 30 years.
Then, from the time I met them last month, to about 30 years in the future (within PNG average life expectancy) that small group I surveyed potentially has a total household population of 800 members.
Suppose those parents and I live to over 65 years of age, then that sample household population may have had a 16-fold increase during our lifetime.
If five kids for every couple is an expected objective, then that small sample of Rai Coast community may go from 25 households (couples) with 50 members to 150 households with 800 members in 30 years.
Even if we say there's a 20% mortality rate, that's still 640 people, for a growth rate of 1,180% in 30 years, or 39.33% annual growth rate (annual population growth rate = [(640-50)/50 x 100]÷30 = 39.33%.
That's scary stuff, a doubling time (Rule of 70) of 1.8 years.
However, I applied the national average household size to this community because that's the size that they gave me when asked about their own observations and expectations.
That's only a microcosm of PNG so it may not be very applicable to other communities in the country, let alone for the national average.
However, if our national population growth rate is even one-tenth of that small community household estimate (3.933% pa), then doubling time is 17.8 years.
If our annual growth rate is one-fifteenth (2.622% pa) of that estimate then our population will double in 26.7 years.
That last figure appears in line with previous estimates from census data and perhaps demonstrates how desktop analysis with the best of intentions may still go astray.
Nevertheless, from using the small community example it's reasonable to suggest that maybe we should ‘expect the best but plan for the worst’ until we obtain direct and incontrovertible evidence of the actual size of our population.
Editor’s note: In 1974, on behalf of the NBC, I presented a paper to a UN population conference in Singapore when the doubling period was 18 years. The PNG population at that time, if my recall is reliable (I am away from home and my papers), was three million – KJ