Contraception

Contraception in FPsim has two parts: the methods that exist, and the choice module that decides who uses which one. They are separate, so you can change the method list without touching choice behavior, or swap the choice model while keeping the same methods.

Methods

A method is an fp.Method with these fields:

Field Meaning
name Short identifier used in code, e.g. inj
label Display name used in plots and interventions, e.g. Injectables
efficacy Proportional reduction in conception probability while using
modern Whether it counts towards modern contraceptive prevalence (mCPR)
dur_use Distribution of how long a user continues before switching or stopping

Note that name and label are not interchangeable. Code that indexes the method dictionary uses name (cm.methods['inj']), while interventions that take method identifiers, such as efficacy scenarios, look methods up by label ('Injectables').

The default method set has ten entries, including none, which represents non-use and makes the method mix sum to one.

Choice modules

The choice module decides, for each woman at each decision point, whether she uses a method and which one. FPsim provides three:

Module Behavior
RandomChoice Uniform random choice among methods; mainly for testing
SimpleChoice Choice depends on age and parity, fitted per location
StandardChoice The default; adds education and wealth to the above

A woman’s decision points are governed by dur_use: when her current method’s duration elapses, she chooses again. This is why dur_use matters as much as efficacy for long-run method mix.

Results

Method usage is reported as method_mix, an array of shape (number of methods, number of timesteps), giving the share of contraceptive users on each method over time. Overall prevalence is reported separately as mcpr on the contraception module.

Because method_mix is indexed by method position, adding a method mid-simulation changes the array’s shape. Index into it via the method’s idx rather than a hardcoded position.

How-to topics

See also