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POPULATION FORECASTING - Logistic CURVE METHOD. GROUP MEMBERS. Kush Poorunsing Aman Sahadeo Arshaad Jeedaran Nevin Sunassee Pamben Moonsamy Kishan Joorawon. Population Forecasting. Important process in the design of waste water treatment plants

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Presentation Transcript
group members
GROUP MEMBERS

Kush Poorunsing

AmanSahadeo

ArshaadJeedaran

NevinSunassee

PambenMoonsamy

KishanJoorawon

population forecasting
Population Forecasting
  • Important process in the design of waste water treatment plants
  • Factors affecting change in population:
    • Fertility/ Birth rate
    • Death rate
    • Migration
logistic method
Logistic Method

Saturation population

  • Follows some logical mathematical relationship.
  • has an S-shape combining a geometric rate of growth at low population with a declining growth rate as the population approaches some limiting value.
equation 1
Equation - 1
  • ………………. (1)
  • Where

Pt: population at some time in the future

Psat: population at saturation level

t: number of years after base year

a, b: data constants

equation 2
Equation - 2
  • ……………….. (2)
  • Where

Psat: population at saturation level

Po: base population

P1, P2: population at time periods

equation 3
Equation - 3
  • …………………. (3)
  • ………………(4)
  • Where

n: time interval between successive censuses

example
Example
  • The data for population censuses from 1851 to 2000 for Island of Rodrigues is given below. Estimate the expected population in 2011.
step 1
STEP 1
  • Three successive years, represented by to, t1, and t2are chosen such that they are equidistant from each other.

t0

t1

t2

step 2
STEP 2
  • The number of years from toto t1and t1 to t2 is denoted by n.

t0

n=28

t1

n=28

t2

step 3
STEP 3
  • The population figures corresponding to to, t1, and t2are Po, P1and P2respectivelythrough which the logistic curve is to pass.

t0

P0

n=28

t1

P1

n=28

P2

t2

calculations 1
CALCULATIONS - 1
  • n=28
  • P0= 11885, P1= 24769 and P2= 35779
  • From equation 2,
calculations 2
CALCULATIONS - 2
  • From equation 3,
  • From equation 4,
calculations 3
CALCULATIONS - 3
  • Replacing the values obtained in equation 1, the expected population for 2011 is:
  • = 2011-1944 = 67 years
conclusion
CONCLUSION
  • Based on census reports, the population of Rodrigues in 2011 was 37,922 (Wikipedia)
  • Estimated population with logistic method is 38420.8
  • 1.31% deviation from actual value
advantages and disadvantages
Advantages and Disadvantages
  • Advantages
    • Longer projection period compared to simple geometric procedures
    • Gives a better approximation than other methods.
    • Disadvantages
    • Mechanical process
    • Cannot predict decreasing population
    • Demographic and socioeconomic changes not considered
    • Requires a large number of observations covering a long period
references
References
  • Punmia, B.C, Arun, K.J., 2005. Water Supply Engineering. 2nd ed. New Delhi: Laxmi Publications
  • Annual Digest of Statistics 2011 [Online]. Available from: http://www.gov.mu/portal/goc/cso/file/AnnualDigestofStatistics2011.pdf
  • Rodrigues [Online]. Available from: http://en.wikipedia.org/wiki/Rodrigues
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