Whole-week first-to-full-bloom peaks were uncertain in four US lilac samples in 1965-2008

We tested whether first-to-full-bloom intervals had local peaks at whole weeks in historical US lilac records. We used 8,384 pairs in four region and period samples. The excess at 7, 14, 21 and 28 days relative to immediate neighbors was 0.60 to 2.85 percentage points. All four state-plus-year cluster intervals included zero after correction for four tests. Alternative neighbors, omission of the seven-day center, equal plant weights, first-bloom flag removal, short-record inclusion and state omissions also gave uncertain results. This extends an earlier leaf-to-bloom diagnostic to a shorter stage interval. It does not establish weekly visits or absence of observation bias. Unknown visits, selected long records, few clusters, different plant types and the assumed local shape of biological gap frequencies limit inference. We provide paired records, a raw-source rebuild, code, source hashes, all estimates and figures. We estimate no climate or pollution effect.

phenology · lilac · observation bias · weekly reporting · flower development · null result