The article presents an analysis of the effects of the list apparentment institution introduced in the electoral rule for the sejmik of voivodship (regional council) and of some other changes which also had significant consequences. The effect analysis of these institutional solutions required primarily a comparison of specific political parties’ election results with the results these parties would have got under the „old” electoral rule, assuming no change in voters’ preferences resulting from the change in law. The electoral rule amendment had a significant impact on the results of specific parties, as measured by the number of mandates gained. Then, the authors investigated a number of alternative coalition strategies available to political parties, elaborating on the issue of effectiveness in actions undertaken by collective actors such as political parties. The authors proved that the results of the elections concerned depended on coalition strategies, rather than on election rules. Some players in the electoral game failed to achieve effectiveness in the attainment of the ultimate objective, i.e. to maximise the number of mandates gained, but the assessment of effectiveness provides different results if we assume that an important objective (though not equally important) was to maximise the results of the relevant bloc formed by apparentment. A matter of concern in the new electoral rule is the violation in 26% of constituencies of the monotonny criterion in the distribution of mandates resulting from the distribution of votes. In their concluding remarks, the authors put forward a proposal for a change in the electoral rule that better reflects the profiles of individual preferences in the social choice, while maintaining the apparentment institution.