In the S-I-R model of parasite and host dynamics, how does the outcome change if we allow new susceptible individuals to be born into the population? When using a t-test, what factors make it more...

In the S-I-R model of parasite and host dynamics, how does the outcome change if we allow new susceptible individuals to be born into the population?

When using a t-test, what factors make it more likely that you will find a significant difference?

Explain why Dutch elm disease might become less lethal to its host over time.