*I create a slider controlling the number of encounters per time
period an
average infected individual has.*

Begin micro-behaviour
**CREATE-ENCOUNTER-RATE-SLIDER**

Begin NetLogo code:
substitute-text-area-for slider-variable-name the-encounter-rate
substitute-text-area-for slider-upper-left-corner-x 625
substitute-text-area-for slider-upper-left-corner-y 10
substitute-text-area-for slider-lower-right-corner-x 875
substitute-text-area-for slider-lower-right-corner-y 50
substitute-text-area-for slider-minimum-value 0
substitute-text-area-for slider-maximum-value 10
substitute-text-area-for slider-increment .1
substitute-text-area-for slider-initial-value 2
create-slider
"slider-variable-name"* ; the name of the parameter (a global variable)*
"slider-upper-left-corner-x" "slider-upper-left-corner-y" *; upper left corner (from the upper left corner of the applet) *
"slider-lower-right-corner-x" "slider-lower-right-corner-y" *; lower right corner *
"slider-minimum-value" "slider-maximum-value" *; minimum and maximum value*
"slider-increment"* ; increment*
"slider-initial-value" *; initial value*

End NetLogo code
## Variants

You can change the location, minimum and maximum values, increment, and
initial value.

## Related Micro-behaviours

RANDOM-ENCOUNTER uses the parameter *the-encounter-rate* defined by
this slider. Together with
CREATE-INFECTION-ODDS-SLIDER this specifies β or the force of infection
in [1].
CREATE-DEATH-RATE-SLIDER,
CREATE-RATE-OF-RECOVERY-SLIDER,
CREATE-FRACTION-VACCINATED-AT-BIRTH-SLIDER and
CREATE-RATE-OF-LOSS-OF-IMMUNITY-SLIDER create related sliders.

## Relation to Mathematical Model

The change in the number of infected is given in [1] as the product of
the force of infection times the number of infected times the number of
susceptible:

β∙I∙S

In this model the expected change is

*the-encounter-rate* ∙ *the-infection-odds* ∙ I ∙ S/N

S/N is the odds that an encounter is with a susceptible individual.

If N (the total population) is constant then

β = *the-encounter-rate* ∙ *weeks-in-a-year* ∙ *the-infection-odds*
/ N

where *weeks-in-a-year* is introduced since *the-encounter-rate* is
given in encounters per week while β is per year. This calculation can be
performed by
MONITOR-FORCE-OF-INFECTION.

## History

This was implemented by Ken Kahn.

## References

[1]
"Mathematical models of vaccination", Almut Scherer and Angela McLean,
*British Medical Bulletin* 2002;62 187-199.