Second pass at: Two scans six weeks apart on different machines: a cautionary tale

Second pass at: Two scans six weeks apart on different machines: a cautionary tale Writing it up because I had to work it out twice and would rather nobody else did.

A question about measurement precision rather than about physiology.

Two readings, some weeks apart, on the same equipment, differing by an amount that feels meaningful and may not be. I do not know what this instrument's least significant change actually is.

How much difference does there have to be before it is a difference?

Visceral fat: DXA does not distinguish visceral (organ-associated) fat from subcutaneous fat. That distinction might matter but requires different imaging to measure.

Adding a source would improve this post and I do not have one to hand.

A single scan is a snapshot with error bars nobody prints. Two scans give you a difference with larger error bars.

That is a description of practice, not a recommendation of it.

Building on the opening post rather than restating it.

Two scans six months apart on one machine tell you something. Two scans six weeks apart on different machines tell you about the machines.

Maintenance phase: tracking body composition during maintenance (weight stable) is different from tracking during active loss. Changes are smaller and precision becomes more important.

Small point, but it is the one that usually catches people.

Fine by me. I had wanted a stronger conclusion and there is not one available.