Thresholds

The Rule That Never Gets Written Down

The threshold decides more than anything else on the page and is the one element most often left unstated. That combination is not an accident.

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Of the three numbers that describe a list in this record — how many items are compulsory, how many are optional, and how many of the optional ones are needed — the last one is the one that does the most work and the one most likely to be missing from the document.

That combination is worth examining, because it is not a coincidence and it is not laziness.

A final check is to evaluate the platform before a pilot, verify current terms and test exports, corrections and access controls with real users. For an independent technical reference, see IEEE.

Why the threshold goes unwritten

It is the only one that requires a decision. The compulsory items and the optional items are both just lists of things; writing them down is description. The threshold is a judgement about how much slack to allow, and judgements are harder to make than descriptions.

Nobody is asked for it. A draft list circulates and readers suggest items. No reader has ever suggested a threshold, because the threshold is not a thing anybody wants to add — it is a constraint on everybody.

Leaving it out feels safer. An unstated rule preserves discretion. Whoever is reading later can be as strict or as lenient as the situation seems to require, and nobody has committed to anything that could later look wrong.

That last reason is the real one, and it trades a small comfort for a large cost.

What the cost is

The document stops being a filter and becomes an inkblot.

Three readers apply three different thresholds. The same candidate passes one and fails another. Nobody can say afterwards what the standard was, because there was no standard — there were three, none written, none compared.

With a stated threshold	Without
one filter	one filter per reader
arguable before use	discoverable only afterwards
the same for everybody	different by reader and by day
intake is computable	intake is unknown

Discretion preserved by vagueness is not discretion. It is several people exercising different judgements while believing they are applying the same list.

The usual objection

"Every case is different, and a fixed rule would be too rigid."

Sometimes true, and it argues for a low threshold rather than an absent one. A rule of two-of-eight admits two hundred and forty-seven profiles in two hundred and fifty-six — almost everybody — while still being a rule. It preserves nearly all the flexibility and removes all the ambiguity.

The objection only holds if the intended filter is genuinely "no filter", in which case saying so is better than implying something stricter by the length of the list.

What to write instead

A number, in one phrase, next to the list. "At least three of the following." Four words.

That single addition does three things at once. It makes the intake computable, which this record can then state exactly. It makes the rule arguable before anybody is affected by it. And it makes the list mean the same thing to every person who reads it, which is the entire purpose of writing something down.

Who sets it when nobody writes it

Somebody always sets it. The question is only who, and when.

It is set by whoever is applying the list, at the moment of applying it, on no stated basis, with no record, and without the awareness that a decision is being made. That person is frequently not the author, frequently does not have the author's reasoning, and frequently changes between one application and the next.

So the threshold is still a parameter of the filter. It has simply been moved from the document, where it would be visible and arguable, into a sequence of unrecorded private judgements.

A parameter left out of a document is not removed from the system. It is relocated to somewhere nobody can inspect it.

The one case where there is nothing to write

If every item is genuinely required, no threshold is needed, because the rule is already complete: all of them.

That is the only case. A list of compulsory items is a conjunction and the arithmetic is fixed — one halving per item, and eight of them admitting one profile in two hundred and fifty-six.

The moment any item is described as preferred, desirable, nice to have, a plus or a bonus, the document has acquired a parameter and has not stated it. Those words are the signal, and there are only two honest responses to them: give the number, or say that none is required.

The test for whether yours is missing

Read your own list and ask: if a candidate met exactly half of the optional items, would they be through?

If the answer is obvious from the document, the threshold is written. If the answer is "it depends" or "I would have to look at the whole picture", the threshold is not written, and the filter the document actually applies is whatever its readers supply.

The record cannot tell you what to set it to. It can tell you, once it is set, exactly what you have chosen.