learn-data-thinking-with-phoebe / Session 1 of 6
Learn Data Thinking with Phoebe · Session 1 of 6

The question behind the question

"Can you look at the numbers and see if the promotion worked?" That sentence arrives in some form at every analyst, every week, and it is not a question. It has no outcome, no population, no timeframe, and no stated decision attached to it, which means four people can hear it and start four different pieces of work, all defensible, three of them useless. Tonight is about the twenty minutes that turn a request into something that has an answer, and about the habit that makes the rest of the course possible: asking what the sentence actually claims before you go and compute anything.

🟢 Everyone Bring a real request somebody sent you No maths, no code 45 min
0-3 · Welcome 3-18 · The four slots, and a claim taken apart 18-40 · Build-along: rewrite three real requests 40-45 · Q&A
Part 0

Where we start

One promotion runs through every session. Daybreak, a coffee subscription company, ran an autumn offer, and three people want to know whether it worked: the founder, the head of marketing, and the person who has to decide whether to run it again in spring. They use almost the same words and they want three different things. By session 4 a bench answers two of their questions and refuses the third, and the refusal is the most useful output of the three.

🎫 Clear all three quiz questions to stamp your passport Live = presented in the 45 minutes Self-study = the full depth, after class

★ What you walk out with tonight. Three real requests from your own work rewritten as questions with all four slots filled, and one of them identified as the sort that cannot be answered with what exists, which is a finding you can send back the same day.

Where this sits on the shelf. Nothing here involves a model, a p-value or a line of code. Training a model and reading its accuracy honestly is learn-intro-ml-with-phoebe. Confidence intervals and hypothesis tests are learn-statistics-with-phoebe. Choosing the chart and checking it is honest is learn-dataviz-with-phoebe. Here the subject is the work that happens before any of those, which is deciding what is being asked and whether it can be answered at all.

Part 1 · covers the four slots

Four slots, and a request is not a question until all four are full

6 min live

The same eleven words, heard by four people, become four different projects. The fix is not to ask "what do you mean"; that gets you a restatement of the same sentence. The fix is to fill four specific slots out loud and let the person correct you.

WHAT ARRIVES "Can you look at the numbers and see if the promotion worked?" 1 · Outcome what counts as worked conversion? order value? customers who stay? 2 · Population who is included everyone? new only? one channel or all? 3 · Timeframe compared with when the weeks before? the same weeks last year? 4 · Decision what changes after run it again in spring, or do not THE SAME REQUEST, ANSWERABLE "Did conversion among new subscribers rise in the twelve weeks after the offer, against the twelve before, enough to run it again?" An empty slot does not stay empty. You fill it with a guess, silently, and nobody finds out which guess until the meeting. Say all four out loud and let them correct you. People cannot specify a question but they can always spot a wrong one.
🔍 Click to zoom - the fourth slot is the one people skip, and it is the one that decides whether the work is worth doing
LiveWhy the decision slot comes last and matters most3 min▶

The first three slots make a question computable. The fourth decides whether computing it is worth anybody's afternoon, and it is the one almost nobody asks about.

Ask it plainly: what will you do differently depending on what I find? Three answers are common, and all three are useful. Sometimes it is specific, which tells you exactly how precise the answer needs to be. Sometimes it is "nothing, I am just curious", which is a fine answer and tells you to spend twenty minutes rather than two days. And sometimes the honest answer is "we have already decided, I need the number for the deck", which is also worth knowing, because that is not analysis and pretending otherwise wastes everybody's time.

The version of this question with the best pedigree is from DARPA, where the Heilmeier Catechism asks a programme manager what they are trying to do in plain language, who cares, what happens if they succeed, and how long it will take. The two that transfer directly into an analysis request are who cares and what difference will it make, and asking them at the start of a piece of work costs one sentence.

Self-studyWhere the four slots come from, and what is behind them4 min▶

This is practitioner craft rather than a research finding, and it is worth being straight about that. There is a long-standing process model for analysis work, CRISP-DM, published by a cross-industry consortium in 2000, and its first phase is business understanding rather than data understanding, which encodes the same idea: you are supposed to establish what decision the work serves before you touch the data. It has six phases in total and it is the ancestor of nearly every process diagram you will see in this field.

Whether it is still the most used process model is a weaker claim than it is usually given. The evidence for the "most used" line rests mostly on two self-selected online polls with a couple of hundred respondents between them; there is a stronger academic literature review showing it dominates among published workflow adaptations specifically, which is a narrower statement. Microsoft's own analytics guidance gives a similar instruction in fewer words, telling you to ask a sharp question, meaning one whose answer is a name, a number or a yes.

None of this is measured. No study shows that teams filling four slots produce better analyses than teams who do not, and nobody appears to have tried. What can be said honestly is that the failure mode is real, common and expensive, and that every process model in the field independently puts a version of this step first.

Part 2 · covers reading a claim

A worked example: the claim everybody repeats about this job

6 min live

You will have heard that data scientists spend eighty percent of their time cleaning data. It is in conference talks, vendor pages and probably in the deck that got your team its budget. It is a useful thing to take apart on the first night, because the taking-apart is the entire skill being built here, and because the answer is more interesting than either "true" or "false".

FOLLOW THE CITATION BACKWARDS A product page "80% of the time" A 2018 blog post cites the one below A 2017 blog post cites the one below A 2016 survey the actual source nobody in the chain re-measured anything; each link quotes the last WHAT THE SURVEYS ACTUALLY SAID 2015 66.7% called cleaning one of their most time-consuming tasks no time percentage given 2016 cleaning and organising 60%, collecting data sets 19% 80% only if you add two these were answers to "what do you spend the most time doing", not shares of a day different tasks together 2017 51% for collecting, labelling, cleaning and organising combined one combined activity 2019 73.5% spend at least 25% of their time on data work a different measure entirely Kaggle 2018 about 11% gathering and 15% cleaning, so roughly 26% combined an independent survey Not one of these is a measurement of how anybody actually spent their time. They are all self-report, and they disagree. The number is not invented. It is two tasks added together in one year of one survey, then copied for a decade.
🔍 Click to zoom - "is it true?" is the wrong question; "what was actually measured, by whom, and how" is the right one
LiveWhat the archaeology shows, and what to take from it4 min▶

Somebody followed the citations properly. A product marketing page cited a 2018 blog post, which cited a 2017 blog post, which cited a 2016 industry survey. Four links, and nobody along the way measured anything new.

At the end of the chain, the 2016 survey asked people what they spend the most time doing and reported cleaning and organising at 60 percent and collecting data sets at 19 percent. Eighty percent appears only if you add those two together, which is not how the survey framed them. Every other year gives a different figure, and an independent survey run by a different organisation put the combined total nearer a quarter. The oldest version of the claim, from a 2014 newspaper article, gives a range of fifty to eighty percent sourced to interviews.

So the honest summary is this: data preparation is a large part of the job, every source agrees on that, and there is no measurement anywhere of what fraction of a day it takes. That sentence is both truer and more useful than the number. It also survives contact with someone who has the survey open in front of them, which the number does not.

One caution about my own sources here, in the spirit of the session: the archaeology above comes from a named practitioner's write-up and a reposted press release. The original 2016 survey PDF would not load on any attempt, so nobody in this chain, including this page, has read the primary document. That is the honest tier, and it is stated rather than hidden.

Self-studyThree questions that take apart any statistic3 min▶

Who measured this, and how? Self-report and observation are different things, and a survey asking "what takes you the longest" is not a time-use study. Most circulating statistics about work are the former dressed as the latter.

What exactly was the denominator? Percentage of what: of people, of time, of projects, of respondents who answered a particular way? The 2019 figure in the table is a proportion of respondents, and the 2016 one is a proportion of respondents naming a task. Neither is a share of a working day, and both get quoted as though they were.

How many links back is the original? If a claim has a source, check whether that source has a source. Two hops is usually enough to find either a real study or a dead end, and finding the dead end takes about five minutes.

Real world

Every organisation has a number like this: a conversion rate, a churn figure, a cost per acquisition that everybody quotes and nobody can source. Finding the origin of one of them is a genuinely useful first week in a new job, and it is the same exercise as the one above.

Part 3 · covers the three askers

Three people, one promotion, three questions

4 min live

Back to Daybreak. Three people ask about the same promotion in almost the same words, and filling the four slots separates them immediately. Two of the three questions can be answered with the data that exists. One cannot, and knowing which is which on day one is worth more than any calculation.

Who asksOutcomePopulationTimeframeDecisionAnswerable?
Head of marketingConversion rateAll orders12 weeks after against 12 beforeRepeat the offer in springYes
FinanceRevenue per orderConverted ordersSame 12 and 12Set next quarter's margin targetYes, with care
The founderWhether they stayCustomers acquired during the offerAt least one renewal cycle laterWhether this is a growth channelNo - the data stops too early
LiveThe founder's question is the important one and the one that has no answer3 min▶

Notice what happened when the four slots were filled in. Everybody said "did the promotion work". Only when you write the timeframe down does it become obvious that the founder is asking about a period the data does not cover, because the rows stop twelve weeks after the offer and a renewal cycle has not happened yet.

That is not a failure. It is the single most valuable thing you can produce on day one, because it arrives before anybody spends a week on it, and because it converts into a concrete request: extend the collection window, or wait, or accept that this question gets answered in the spring rather than now. Session 2 turns that into a written gap list.

The failure mode is answering a nearby question instead. The founder asks about retention, the data supports activation, so the deck reports activation and the sentence "the promotion worked" is said out loud. Nobody lied. Nobody checked. The organisation now believes something it has no evidence for, and it will plan the spring around it.

Build-along

Rewrite three real requests

★ 22 min · your own inbox

Three requests somebody actually sent you. Not hypotheticals, because hypotheticals are already well specified and that is what makes them useless here.

Find three. Search your messages for "can you look", "do we know", "how many", "is it working". Take the three most recent, whatever they are about.

Fill what you can. For each, write the four slots using only what is actually in the message. Resist completing them from memory or common sense; the point is to see what was genuinely specified.

Mark the gaps. Circle every slot you filled with a guess. Most requests specify one or two slots out of four, and the outcome slot is the one most often assumed rather than stated.

Write the reply. One line per gap, phrased as a proposal rather than a question: "I will read this as conversion among new subscribers, twelve weeks either side - tell me if you meant something else." People correct a proposal instantly and stall on an open question.

Ask the fourth slot explicitly on at least one of them: what will you do differently depending on what I find? Note the answer, because it decides how much of your week this deserves.

Propose, do not interrogate. "What exactly do you mean by worked?" puts the work back on them and they will repeat themselves. "I will read this as X" gets corrected in seconds.

Write the timeframe as two windows, not one. "After the promotion" is not a timeframe until you say what it is being compared with, and that comparison is where session 4's trouble starts.

Name the population in rows, not in words. "New customers" is a word; "orders where the customer had no previous order" is a row filter, and the gap between those two is where a week gets lost.

If the decision slot comes back empty, that is still an answer. Spend twenty minutes, send a number, move on.

Keep the three rewritten questions. Session 2 turns them into lists of what you would need, and session 4 answers one of them properly.

Send at least one reply tonight. The habit is the thing being built here, and it only becomes a habit if it survives contact with a real colleague.

If you take one thing from tonight. An unfilled slot never stays empty. You fill it with a guess, silently, in the first five minutes, and nobody discovers which guess you made until the work is presented. Saying the guess out loud at the start costs one sentence and is the cheapest thing in this entire course.

Homework

Before session 2

25 min
  1. Send the replies for all three requests and note what came back. The corrections are the data: people will correct the outcome slot far more often than the other three, which tells you where the ambiguity actually lives.
  2. Trace one number your organisation quotes. Pick something everybody repeats and find where it came from. Two hops usually reaches either a real source or a dead end, and both are worth knowing.
  3. Find one request you answered in the last month where you now think you guessed a slot wrong. Write what you assumed and what they probably meant. Nobody has zero of these.
  4. Bring the three rewritten questions to session 2, which asks what you would need to know to answer each one, before looking at what you actually have.
Check yourself

Three questions

Clear all three and session 1 gets stamped in your passport.

1 · Somebody sends you "can you see if the new onboarding is working?" What is the most useful first reply?

An open question puts the work back on somebody who has already told you everything they can articulate, and you will get the same sentence again. A proposal gets corrected in seconds because people cannot specify a question but can always spot a wrong one. The decision slot rides along in the same message.

2 · The "80% of time cleaning data" claim. What is the accurate thing to say about it?

The interesting answer is neither true nor false. Data preparation being a large part of the job is agreed by every source; the specific number is two tasks added together in one year, then copied down a chain in which nobody re-measured. Saying the honest version survives contact with somebody holding the survey.

3 · Filling the slots reveals that the founder's question needs data from a period the rows do not cover. What do you do?

Discovering a question is unanswerable on day one is the most valuable output available, because it arrives before a week is spent and converts into a concrete request. Answering the nearby question instead is how an organisation ends up believing something nobody ever demonstrated.

Sources covered

What this session teaches, and where it came from

✓The Heilmeier CatechismAll eight questions read from DARPA's own page; cross-checked line by line against a raw fetch
✓CRISP-DM's six phases and 2000 originRead from the primary consortium document
✓The citation chain behind the 80% claimFour links, traced by a named practitioner who followed and linked each one; the year-by-year survey figures come from that write-up and a reposted press release
◐The original 2016 survey documentNever loaded on any attempt, so no one in this chain has read the primary; stated on the page rather than hidden
◐"CRISP-DM is still the most used"Rests on two small self-selected polls plus one literature review covering published adaptations; the narrower claim is the defensible one
◐The four slots themselvesPractitioner craft. No study shows teams that do this produce better analyses; every process model in the field puts a version of it first

Every fact on this page, and its verification tier, is recorded in the course's source map.

Session 1 cheat sheet · pin this

Four slotsOutcome, population, timeframe, decision.
Propose, do not ask"I will read this as X" gets corrected. "What do you mean" gets repeated.
The fourth slotWhat changes depending on the answer? It sets the budget.
Empty is never emptyYou filled it with a guess in the first five minutes.
Two hops backDoes the source have a source? Five minutes finds the dead end.
Unanswerable is an answerSay it day one, and say what would answer it.