Interesting. Did you look at the polling stations at the irregular spikes? What is their number, rather than percentage. The absoulte number (even better, the number of voters in them) would indicate what effect hey had on the overall results. Also what regions are they in? In some very sparsely populated regions, like North Siberia, where "mobile" polling stations are used, the number of voters would be very small, but probably the attendance would be close to 100%, and I would not be surprised if they all voted for United Russia. Or, this may be due to some other peculiarity of counting what constitutes a polling station (stations abroad, the voting mechanism for people who were travelling on the day of the elections, etc). Also, please do confirm where the data comes from - is it publicly available?