Pt - Po = (B-D) + (I-O)
( Change in Population ) = ( Natural Decline, Births - Deaths) + ( Net Immigration)
I-O= ( Pt - Po) - (B - D)
following a cohort of of people aged 30-34 in 2005 to the age of 35- 40 in the year 2010:
How many of the "N" people will be alive five years later?
If all were 30: l35 / l30
If all were 34: l39 / l34
Approximate by assuming all are 32.5: l 37.5 / l 32.5
survival fraction (approx) = l37.5/ l 32.5
= .5( l35 + l40)/ .5 ( l30 + l35)
= 5L35 / 5L30
3 Ways to Estimate Using S= 5L35 / 5L30
1) forward : compare SxN expected 35-40 year olds in 2010 to the actual count
2) backward: take (1/S) x actual count of 35 - 40 year olds in 2010 and compare to N
3) average: 1 + 2
What proportion of 30-35 year olds will be alive 5 years later?
5L30 = 491,460
5L35 = 489,248
S= 489,248 / 491,460 = .99550
observe 22,819 30-34 in 2005
23,016 35-40 in 2010
1) forward: expected 35-39 in 2010 = (.99550)(22819)
= 22716
observed 35-39 in 2010 = 23016
observed - expected = 300 ( net migration )
2) backward: expected 30 - 34 in 2005 = 22819
observed 30-34 in 2005 = (1.00452) (23016) = 23120
observed - expected = 22819 - 23120 = - 301
301 net migrants
3) average : 300 + 301 / 2 = 300.5
What percent of 30-34 year olds will survive the next 30 years to be counted as 60-64 year olds?
sL60 / sL30 = 443296/ 49460 = .90199