Question

biointeractive modeling disease spread
c. using this table, the \sir data table,\ and/or the \sir graph\ in the click & learn, describe how the number of individuals in each group changed throughout the outbreak (i.e., from day 0 to the last day of the outbreak)

1. following the guidance of your instructor, download, print, or sketch an image of your graph. make sure to include your graph when submitting this worksheet, in whichever format your instructor asks for
2. examine each curve (line) in the graph individually, then fill in the table below. for each group in the first column:

a. in the second column, describe how the curve representing the number of individuals in that group changes throughout the outbreak
b. in the third column, describe where individuals in that group move to. for example, for the first row, which other group(s) can susceptible individuals move to? write
one\ if no groups fit
c. in the fourth column, describe where individuals in that group come from. for example, for the first row, which other group(s) can susceptible individuals come from? write
one\ if no groups fit

group	how does this groups curve change over time?	where do individuals in this group move to?	where do individuals in this group come from?
susceptible
infectious
removed

review the \summary\ section of the \sir model basics\ module to learn more about the graph.

1. consider the relationship between the three curves on the sir graph. refer to your answers in question 12 as you consider how individuals move between the three groups:

a. what happens to individuals in the susceptible group over time?
b. what happens to individuals in the infectious group over time?
c. how many days did it take to reach peak infection (the day with the most infectious individuals)?
d. during peak infection, how would you describe the movement of individuals in the infectious group?
e. what happens to individuals in the removed group over time?
f. do individuals enter the susceptible group or leave the removed group in this model? why or why not?
published march 2023 page 4 of 10

Explanation:

12.
a. For the Susceptible group, the curve typically shows a decrease over time as individuals become infected. For the Infectious group, it usually has a rise - peak - decline pattern as the number of new infections first increases, then reaches a peak, and finally decreases. For the Removed group, the curve shows an increase over time as more individuals recover or are otherwise removed from the infectious cycle.
b. Susceptible individuals move to the Infectious group when they get infected. Infectious individuals move to the Removed group when they recover or are isolated. In the SIR model, there is no movement from the Removed group back to the other groups typically.
c. Susceptible individuals come from the initial population at the start of the outbreak and there is no inflow from other groups in the basic SIR model.

13.
a. Over time, individuals in the susceptible group decrease as they get infected by the infectious individuals.
b. Individuals in the infectious group first increase as they infect susceptibles, then peak when the number of new infections starts to decline, and finally decrease as they recover and move to the removed group.
c. The number of days to reach peak infection varies depending on the parameters of the SIR model (such as the infection rate and recovery rate) and the initial conditions.
d. During peak infection, a large number of individuals are moving from the susceptible group to the infectious group, and also a significant number of infectious individuals are moving to the removed group.
e. Individuals in the removed group increase over time as more infectious individuals recover or are otherwise removed from circulation.
f. In the basic SIR model, individuals do not enter the susceptible group (no birth or re - susceptibility) and do not leave the removed group (no re - infection or re - entry into the population at risk).

Answer:

12.
a. Susceptible: Decreases over time. Infectious: Rises, peaks, then declines. Removed: Increases over time.
b. Susceptible to Infectious. Infectious to Removed. None for Removed to other groups.
c. Initial population. None from other groups.
13.
a. Decrease as they get infected.
b. First increase, then peak and decrease as they recover.
c. Varies based on model parameters and initial conditions.
d. Many move from Susceptible to Infectious and from Infectious to Removed.
e. Increase over time.
f. No. In basic SIR, no birth/re - susceptibility and no re - infection/re - entry from removed group.