The first thing to note is that the County Council elections in 2012 saw a turnout of just over 37%. Turnout for the by-election was 35%.
Secondly, Hengoed is a two member ward. This complicates matters slightly, but Plaid, Labour and People First all had two candidates in 2012, and so it is simple to calculate their share of the vote for both elections.
In absolute terms, Labour and Plaid stood still. George Edwards polled 338 votes in 2012, while Penny Edwards polled 335. Martin Davies for Plaid polled 313 votes this time (315 in 2012) and lost out by 22 votes (23 votes in 2012).
The two parties were neck and neck, in other words.
More interesting is the parties' share of the vote.
Labour's share rose from 28% to 33%. +5%
Plaid's share rose from 28% to 31% +3%
The biggest shift occurred in the performance of Siân Caiach's People First which saw its share drop from 29% to 8%.
Ukip, which did not contest the 2012 election, took 15% of the vote, which is only slightly higher than their current poll ratings across the UK which are hovering around the 12% mark.
On that basis it looks very much as though the main story here was a switch from People First to Ukip, which just happen to be at opposite ends of the political spectrum.
As expected, it was a very close race for the county council seat in the Hengoed by-election, with Labour beating Plaid by just 22 votes. The turnout was just 35%.
Labour - 335
Plaid Cymru - 313
UKIP - 152
People First - 80
Independent - 76
Conservative - 54
Penny Edwards is thus elected for Labour.
Susan Phillips for Plaid won the election for the vacant seat on Llanelli Rural Council by a rather more comfortable margin:
People First 65
The result leaves Labour with 22 councillors on the County Council, while Plaid has 29.