  Analysis of the transit timing variations (TTVs) of candidate pairs near
mean-motion resonances (MMRs) is an effective method to confirm planets.
Hitherto, 68 planets in 34 multi-planet systems have been confirmed via TTVs.
We analyze the TTVs of all candidates from the most recent Kepler data with a
time span as long as about 1350 days (Q0-Q15). The anti-correlations of TTV
signals and the mass upper limits of candidate pairs in the same system are
calculated, using an improved method suitable for long-period TTVs. If the
false alarm probability (FAP) of a candidate pair is less than 10^{-3} and the
mass upper limit for each candidate is less than 13 M_J, we confirm them as
planets in the same system. Finally, 8 planets in 4 multi-planet systems are
confirmed via analysis of their TTVs. All of the 4 planet pairs are near
first-order MMRs, including KOI-2672 near 2:1 MMR, KOI-1236, KOI-1563 and
KOI-2038 near 3:2 MMR. Four planets have relatively long orbital periods (> 35
day). KOI-2672.01 has a period of 88.51658 days and a fit mass of 17 M_\oplus.
It is the longest-period planet confirmed, to date, near first-order MMR via
TTVs.
