There is much general information in the link that can be informative and useful for new members. I totally agree that there are optimal levels that should be considered, rather than the entire reference range. Optimal levels can even vary from one person to another.
I don't agree that the optimal levels are basically the middle area of the current ranges, as shown in the article. The reason I say that is that the data base used to calculate reference ranges includes all test data for people whose TSH falls within its very broad range. We all know how poor TSH is as a diagnostic for hypothyroidism. So that means the data base includes some hypo patients whose TSH is in the upper end of the TSH range. In addition, hypo patients with central hypothyroidism are not excluded because their TSH would generally fall in the lower part of its range. So all those hypo patients' data would also be included.
The end result is that the test data bases for Free T3 and Free T4 include a lot of data from hypothyroid patients. As a result, the calculated ranges are far too broad. If the data bases were purged of suspect hypothyroid and hyperthyroid patients, and the reference ranges were calculated based only on healthy adults with no known thyroid pathology, the ranges would look more like the upper half of the current ranges. So my optimal ranges would be more like the upper half of the current ranges.
Accordingly, we hear from lots of members with FT4 and FT3 around the middle of current ranges, yet they still have hypo symptoms until they get their FT3 up toward the high end of the range. Obviously there are exceptions because, as mentioned, people are different in their requirements, and there are other factors as well, such as Vitamin D, B12, and ferritin levels. And sometimes the adrenal system is a factor also.
I agree with gimel that there's good general information, but we don't all feel best/optimal in the middle of the ranges - few of us do, that we see on the forum - most, but certainly not all, seem to feel best with FT4 about mid range and FT3 upper half to upper third of the range.
The article also doesn't take into account that AACE/ATA have recommended that the reference range for TSH should be adjusted down to 0.3-3.0 and that most labs (and doctors) have failed to accept that change.
It also doesn't take into account that many of us will have suppressed TSH when taking any type of thyroid replacement hormone and even with suppressed TSH, FT levels can be low normal and symptoms can be present.