Variable name | Additional information variable | Parameter estimates | Interpretation of effect |

Age | 0.005** | The older, the more likely to donate | |

Gender | Reference group, male | −0.03 | No effect of gender |

Political orientation | Reference group, liberal | ||

Conservative | −0.16** | Conservative voters less likely to donate than liberal voters | |

Won’t tell | −0.13 | Donation likelihood of won’t-tellers not significantly different from liberal voters | |

Donation_{t−1} | Donated at t − 1 (0 = no; 1 = yes) | 0.96*** | When donated last time, one is more likely to donate now |

Donation first observation | Donated at first observation (0 = no; 1 = yes) | 0.79*** | When donated first time in observation period, one is more likely to donate now |

CompNegDiff | Tests effects of negative difference in number of questions when not donated last time (0 = equal number of questions; 1 = substantially less questions at t than at t − 1) | 0.40*** | When number of questions is substantially lower now than last time, one is more likely to donate than if the number of questions is equal |

CompPosDiff | Tests effects of positive difference in number of questions when not donated last time (0 = equal number of questions; 1 = substantially more questions at t than at t − 1) | 0.12** | When number of questions substantially larger now than last time one is more likely to donate than if number of questions is equal |

Donation_{t−1}* CompNegDiff | Tests difference of effect CompNegDiff when donated last time | −0.48*** | If donated last time, positive impact of CompNegDiff gets “neutralized” (0.40 + −0.48 = −0.08 ^{†}) |

Donation_{t−1}* CompPosDiff | Tests difference of effect CompPosDiff when donated last time | −0.30*** | If donated last time, positive impact of CompPosDiff becomes negative (0.12 + −0.30 = −0.18 ^{‡}) |

Constant | Constant | −1.24*** | |

σ^{2} | Variance component of the randomized intercept | 0.59 |

**P* < 0.05

***P* < 0.01

****P* < 0.001

†This parameter estimate of −0.08 was not significant (*P* = 0.210).

‡This parameter estimate of −0.18 was significant (*P* = 0.002).