Structured sexual network
Class: sti.StructuredSexual | Base class: ss.SexualNetwork
The StructuredSexual network is STIsim's primary sexual contact network. It is created automatically when you make a sim.
Overview
Agents are assigned a risk group (low, medium, high) at initialization. Risk group determines partnership patterns: concurrency, relationship type, and duration. Partnerships form each timestep based on age preferences, dissolve after their sampled duration, and are classified as stable, casual, one-time, or sex work.
Risk groups
| Risk group | Description | Female share | Male share |
|---|---|---|---|
| 0 (low) | Marry and remain monogamous | 85% | 80% |
| 1 (medium) | Marry then divorce, or have concurrent partners | 14% | 18% |
| 2 (high) | Never marry | 1% | 2% |
Partnership types
How a partnership is classified depends on the risk groups of both partners:
- Stable: Both partners in the same risk group and pass a stability check (RG0: 90%, RG1: 50%, RG2: 0%)
- Casual: Mismatched risk groups, 50% chance (otherwise one-time)
- One-time: Single-timestep contact
- Sex work: FSW-client contacts, one-time duration
Concurrency
The number of concurrent partners an agent seeks depends on their sex and risk group:
| Low (RG0) | Medium (RG1) | High (RG2) | |
|---|---|---|---|
| Female | 0.0001 | 0.01 | 0.1 |
| Male | 0.0001 | 0.2 | 0.5 |
Values represent the parameter of a Poisson distribution (+1), so a male in RG2 typically seeks 1-3 concurrent partners.
Age mixing
Women sample a preferred partner age from a normal distribution. Parameters vary by female age group and risk group:
| Female age group | RG0 (mean, std) | RG1 | RG2 |
|---|---|---|---|
| Teens (<20) | (7, 3) | (6, 3) | (5, 1) |
| Young (20-25) | (8, 3) | (7, 3) | (5, 2) |
| Adult (25+) | (8, 3) | (7, 3) | (5, 2) |
Values are the age difference (male minus female) in years. Partners are matched by sorting both groups by age.
Sex work
| Parameter | Default | Description |
|---|---|---|
fsw_shares |
5% | Proportion of women who are sex workers |
client_shares |
12% | Proportion of men who are clients |
sw_seeking_rate |
1/month | Rate at which clients seek FSWs |
Coital acts and condoms
| Parameter | Default | Description |
|---|---|---|
acts |
lognorm(80/yr, 30/yr) | Coital acts per partnership per year |
condom_data |
None | Condom use probability (can be stratified by risk group) |
Transmission probability per partnership accounts for both condom use and number of acts:
P(transmission) = 1 - [1 - beta * (1 - eff_condom)]^(acts * p_condom) * [1 - beta]^(acts * (1 - p_condom))
Other networks
STIsim also includes:
ss.MaternalNet: Mother-to-child transmission network (created automatically)sti.AgeMatchedMSM: Men-who-have-sex-with-men network with age-based matchingsti.PriorPartners: Stores former partners for contact tracing (opt-in viarecall_prior=True)