07Daily check-ins are subjective.
Sleep quality, energy, mood, mental sharpness, calm and wellbeing are member-entered ratings on a 1–10 scale. They are real and they matter, but they are a person's impression of their day, not an instrument reading.
08Some fields do not mean what their name says.
In the check-in data, mood and overall wellbeing are the same underlying field, so we never report them as two independent confirmations. The field named stress behaves as a calm score where higher is more relaxed. We publish these quirks rather than quietly working around them.
09Lab noise can be bigger than the effect.
Every blood test has test-retest variability. HDL's noise floor is roughly ±7–8%, which is why we retracted a community-wide 4.6% HDL decline: the signal was smaller than the noise. Where a change sits inside the assay's own variability, we say so.
10Units and naming are a minefield, and it has bitten us.
The same biomarker arrives from different labs under different names and in different units. ApoB and apolipoprotein_b are the same thing; LDL cholesterol, LDL particle number and LDL size are three different physical quantities that a careless match will average together into nonsense. Genotype arrives spelled four different ways. One naive match once discarded 866 of 1,277 members without any error appearing. We now canonicalise names, convert units explicitly, and print what we folded together.
11Timing and lag are uncertain.
We know when a member logged a start. We do not always know when they actually started, whether they took it consistently, or at what dose. Dose is recorded on about 57% of entries and time of day is not captured at all. A follow-up blood test 77 days later is a real measurement at a real time, but the exposure between those two points is partly inferred.
12Coverage is incomplete.
Not every member wears a device, retests on schedule, or logs every day. Missing data is rarely missing at random: people log more when things are going well.