membershipgrowthdecay

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WHAT IS IT?

A model to see how membership of the Craft can grow or decline depending on introduction of new members by present members, rate of attrition due to resignation and death.

HOW IT WORKS

Probability of dying is a function of age. With each tick a member's age would grow older by one year, and the probabiltiy of dying is a function of -0.42084975 + 0.00801353*age. r=0.8489 df = 91 p < 0.00001 (calculation based on data from US Social Security website. https://www.ssa.gov/oact/STATS/table4c6.html, last accessed 18/9/2020) The asumption that each year 5% of the members will leave the Craft, observe what might happen.

Another assumption, a lodge with 40 people is able to introduce 4 new members each year, i.e. probability of each member introducint a new member is 0.1

These paramaters coud be changed

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Globals [

        ]


turtles-own [
             age
             %NewMember
            ]

to setup
  ca
  reset-ticks
  clear-plot
  crt  40
  [ set shape "person"
    set color blue                 ;; blue = master mason
    setxy random-xcor random-ycor
    set size 2
    set age random 30 + 40
    ;; chance of introducing a new member each year.
    set %NewMember random-normal (likelihood-introduce / 100) 0.1
  ]

  ask n-of 3 turtles [set color white] ;; white = EA or FC
end 

to go
  ; each tick represent 1 year
  ; check for advancement of EA/FC to blue
  ; check for resignation, assuming %resignation


  ; check for additional member. Only MM can introduce new member
  ask turtles with [color = blue] [ if random-float 1 < %NewMember [hatch 1 [ set age random 30 + 30
                                                 set color white
                                                 set shape "person"
                                                 set size 2
                                                 setxy random-xcor random-ycor
                                                 set %NewMember random-normal (likelihood-introduce / 100) 0.1
                                                ]
                                        ]
                                  ]

  ;; check for resignation.
  ask turtles [if random-float 1 < (percent-resigned / 100) [die]
               ]

  ;; check for -> MM
  ask turtles with [color = white] [
                                    if random-float 1 < 0.9  [set color blue]  ; 90% chance of becoming MM in one year
                                   ]

  ;; add 1 year to age and check for deaths
  ask turtles [ set age age + 1
                let probability-of-dying chance-of-dying age
                if random-float 1 < probability-of-dying [die]
               ]


;  draw-histogram
;  plot-EA/FC
  tick
  if count turtles < 7 [stop]  ; if less than 7 members, the lodge dies
  if ticks > 150 [stop]
end 

to-report chance-of-dying [declared-age]
  let %dying -0.42084975 + 0.00801353 * declared-age
  report %dying
end 

to draw-histogram
  histogram [age] of turtles
  set-plot-x-range 30 80
  set-histogram-num-bars 10
end 

to plot-EA/FC
  plot count turtles with [color = white]
end

There is only one version of this model, created over 4 years ago by Ronald Paul Ng.

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