Reading a claim about your sleep

This is the last lesson, and it has two jobs and one refusal.

The first job is to give you two habits for the next claim about sleep you meet: the institute's standing sort, which you've used before, and one question this course adds to it. The second job is a decision about your own sleep, which you make and this course does not. And the refusal is the reason the lesson exists at all, so it gets a section of its own.

Habit one: sort the claim

The sort is three categories, and Memory lesson 7, Note-Taking lesson 8 and the other closing lessons on the Core path all use it. Measurable: a study could check it. Unmeasurable as stated: it uses a term nobody has pinned down. False: it has been checked and did not hold.

It is used here, not re-taught. The four claims below are specimens written for this lesson, not quotations from anywhere, and the sorting of each is this course's reasoning.⁸

One. "Adults need seven or more hours a night." Measurable, but notice what kind of sentence it is before you sort it. It is a recommendation, and lesson 3 read the statement it comes from with its verb: "Adults should sleep 7 or more hours per night on a regular basis to promote optimal health."² A recommendation is a panel's decision about a literature, and the outcomes the statement lists are introduced with "is associated with". So the sort is "measurable", and what was measured is not the sentence as the specimen states it, which drops the panel's "should" and turns advice into a fact about your body.

Two. "Your body repairs itself while you sleep." Unmeasurable as stated. Repairs what, measured how, compared with what? Nothing in the sentence says what would count against it. That does not make it wrong. It makes it a framing, and a framing can't be checked until somebody turns it into a claim with a quantity in it.

Three. "Everybody needs eight hours." False, as a statement of what the field says. The consensus statement says seven or more, sets no upper bound for healthy adults, and says that "Individual variability in sleep need is influenced by genetic, behavioral, medical, and environmental factors."² Eight is a number people remember; the panel printed seven or more.

Four. "Night owls die younger, so get to bed by ten." Two claims welded. The first is measurable, and this course has read nothing on it: lesson 4 had chronotype and the shift-work classification, and neither is a mortality figure for late sleepers. The second is advice about your life, and it is also a claim about when, which the first half would have to have been measured on. Each half needs its own verdict, and the first gets "not something this course can tell you".

Habit two: the clock question

Three earlier courses on the Core added a question to the sort. Memory added the sample: how many people, and who. Focus and Deep Work added the instrument. Note-Taking added the setting. This course adds the clock question.

Is this claim about how much sleep, or about when?

Lesson 4 introduced it. In this course's reading most of the claims people meet are about duration, and a sentence about one licenses nothing about the other.⁸ They're different quantities, measured with different instruments and with different gold standards: electrodes in a laboratory for how much, a hormone assay under dim light for when.¹⁶

Then, once you know which quantity, the question that comes with it: which instrument produced the number?

Try it on a sentence you might actually say. "My watch says I've been getting six and a half hours, so I'm below the recommendation." It is about how much, so far so good. Now the instrument. The watch is a consumer device, and lesson 1's comparison found such devices had high sensitivity and low specificity: "epoch-by-epoch sensitivity was high (all ≥0.93), specificity was low-to-medium (0.18–0.54)".¹ So they tend to count quiet wakefulness as sleep, and on a night with a lot of lying awake that pushes the total up. How far, and whether it outweighs the sleep they miss, the abstract does not say. That reasoning is this course's.⁸

And the recommendation's number rests on whatever instruments the cohorts behind lesson 3's associations used, which this course did not read.³ Nothing says they were watches. Comparing a watch's figure to that recommendation may be comparing two instruments, and nobody has told you the exchange rate between them.⁸

The sources side by side

The sources in this course that measured something, plus the panel's recommendation they're most often quoted beside. The second column is the sources'; the rest are this course's record and reading.⁸

The guidelines in lesson 6 and the documents in lesson 7 are not in the table. The guidelines are judgements about trials, and lesson 7's documents are arguments about sentences.

Read the fourth column. Five of the eight are about how much, two about when, and one compares sleep with waking. That is the shape of what this course read.

And read the last column against the headline versions of these sources that this course has quoted. In every row the licence is narrower, and in every row something real survives.

The refusal

Here's the question most readers came to this course hoping it would answer: how much sleep do I need?

This course can't tell you. That is not modesty, and it is not a way of avoiding the subject. It is the honest reading of three facts that sit side by side.

The population recommendation is seven or more hours. "Adults should sleep 7 or more hours per night on a regular basis to promote optimal health."² It is a recommendation for a population, from the field's peak bodies, and its list of outcomes is stated as associations.

Some people sleep much less by nature. A university's release on work by Ying-Hui Fu, Louis Ptáček and colleagues reports that "people who had inherited a particular mutation in a gene called DEC2 averaged only 6.25 hours of sleep per night; study participants lacking the mutation averaged 8.06 hours", and that "this mutation is rare, so while it helped explain some natural short sleepers, it couldn't account for all of them."⁹ So the release calls that one mutation rare, and says it does not explain every natural short sleeper. This course read the release, not the papers, and the release reports how long people slept, not what they need.

And feeling fine does not tell you which group you're in. In lesson 2's experiment, the people held to six hours in bed, which means less than six hours asleep, grew sleepier at first and then barely sleepier, while their performance kept falling for a fortnight. The authors take that to suggest the participants "were largely unaware of these increasing cognitive deficits".⁴ "I feel fine on six" is what somebody who naturally sleeps less would say, and on that reading it is also what a restricted participant might have said while their performance fell.

That refusal cuts both ways, and both matter. It won't give you the reassuring number, that six is fine for you. And it won't give you the alarming one either, that you're damaging yourself below seven. Neither is something this course can know about one reader.

Three things people get wrong

"Somebody must have checked." Somebody checked one chapter of lesson 7's book, and he reports it took him more than 130 hours. For a claim you meet, the question is whether you can see who checked and how far they read, which is what the read-level column above is for.

"The science says eight hours." The consensus statement says seven or more, sets no upper limit for healthy adults, and says need varies. Eight is a number people remember; the panel printed a different one.

"If I feel fine, I am fine." The restricted sleepers in lesson 2 grew only a little sleepier after the first days while their measured performance fell for two weeks. How you feel is worth knowing, and it is a different instrument from how you perform.

Practice

Connections

Back. To the whole course. Lesson 1's instruments are habit two's second question. Lesson 2 is why feeling fine is not evidence. Lesson 3's verb is why a recommendation is not a finding. Lesson 4 is the clock question. Lesson 5 is design as the reason a figure changes. Lesson 6 is where a decision stops being yours alone. Lesson 7 is what a claim looks like after it has been compressed.

Forward. Nowhere on the Core path depends on this course. What it hands on is the clock question, which is worth asking of any claim about a body that has a daily rhythm, and the refusal.

Go deeper

• The consensus statement, open access. Two pages. This course read the recommendation and four statements. Read it whole, since it is short, and notice the sentence on more than nine hours.
• The UCSF release on the short-sleep genes, 28 August 2019. Read here as a release, not the papers behind it. The second paper is in Neuron; this course opened none of them.

Sources

1. Evan D. Chinoy and colleagues, "Performance of seven consumer sleep-tracking devices compared with polysomnography", Sleep 44(5), 2021, zsaa291. Abstract read in full; the paper was not opened. Supports: the sensitivity and specificity figures, polysomnography as the gold standard for how much, and the worse performance on disrupted nights.
2. Nathaniel F. Watson and colleagues, "Recommended Amount of Sleep for a Healthy Adult", Sleep 38(6), 2015, pp. 843 to 844. Read in part: the recommendation and four statements. Supports: the recommendation, its associational list, and the sentence on individual variability.
3. Francesco P. Cappuccio and colleagues, "Sleep duration and all-cause mortality", SLEEP 33(5), 2010, pp. 585 to 592. Read in part, in fragments. Supports: the sample size and the associational reading. How the cohorts measured sleep was not read, and the body says so.
4. Hans P. A. Van Dongen and colleagues, "The Cumulative Cost of Additional Wakefulness", SLEEP 26(2), 2003, pp. 117 to 126. Abstract read in full; the paper was not opened. Supports: the design, the sample across both experiments, the sleepiness ratings, and "largely unaware" as the authors' reading of them.
5. Melissa A. St Hilaire and colleagues, "Human phase response curve to a 1 h pulse of bright white light", The Journal of Physiology 590(13), 2012. Abstract read in full, plus one sentence of the introduction. Supports: the direction of the shift.
6. Neda Ghotbi and colleagues, "The µMCTQ", Journal of Biological Rhythms 35(1), 2020. Read in part: the abstract and the measure. Supports: the hormone assay as the gold standard for when, and the questionnaire as its approximation.
7. Sabrina Berres and Edgar Erdfelder, "The sleep benefit in episodic memory", Psychological Bulletin 147(12), 2021. Read in part, from the accepted manuscript. Named in the table only.
8. The course's own constructions, labelled where they appear. The four specimens and their sorting; the view that most claims people meet are about duration; the reasoning about which way a watch's error runs and about comparing a watch to the recommendation; the guess about how a mortality study would measure "night owl"; the table's selection and its last three columns; the view that worrying about sleep has costs; and the view that leaving a reader without a number is more honest than giving one.
9. University of California, San Francisco, "After 10-year search, scientists find second 'short sleep' gene", 28 August 2019. Read in part: the university's own news release. Neither the papers it reports nor any other paper on short sleep was opened. Supports: the DEC2 figures and the sentence on how rare that mutation is.