def sensitivity_metric(event_id_1, event_id_2):
    """Determine similarity between two epochs, given their event ids."""
    if event_id_1 == 1 and event_id_2 == 1:
        return 0  # Completely similar
    if event_id_1 == 2 and event_id_2 == 2:
        return 0.5  # Somewhat similar
    elif event_id_1 == 1 and event_id_2 == 2:
        return 0.5  # Somewhat similar
    elif event_id_1 == 2 and event_id_1 == 1:
        return 0.5  # Somewhat similar
    else:
        return 1