Pay-it-forward and standard of care | ICC | 0.01 | 0.05 |

Proportion in control group | 0.06 | 0.06 | |

Superiority margin | 0.2 | 0.2 | |

Proportion in intervention group assuming H0 | 0.26 | 0.26 | |

Proportion in intervention group assuming H1 | 0.54 | 0.54 | |

Difference at which power is calculated | 0.48 | 0.48 | |

Number of people per cluster | 10 | 10 | |

Alpha | 0.05 | 0.05 | |

Power | 0.8 | 0.8 | |

Total sample size per arm | 30 | 40 | |

Number of clusters per arm | 3 | 4 | |

Pay-what-you-want and standard of care | ICC | 0.01 | 0.05 |

Proportion in control group | 0.06 | 0.06 | |

Superiority margin | 0.2 | 0.2 | |

Proportion in intervention group assuming H0 | 0.26 | 0.26 | |

Proportion in intervention group assuming H1 | 0.42 | 0.42 | |

Difference at which power is calculated | 0.36 | 0.36 | |

Number of people per cluster | 10 | 10 | |

Alpha | 0.05 | 0.05 | |

Power | 0.8 | 0.8 | |

Total sample size per arm | 80 | 110 | |

Number of clusters per arm | 8 | 11 |