Questions a table cannot answer

By the end of this lesson you can recognise when the data you have cannot answer what you asked.

Why it matters

The most useful thing an analyst can say is sometimes: "This data cannot answer that, but here is what it can tell us, and here is what we would need." Saying it early saves people from decisions built on guesses.

The idea in plain words

Think of a school register. It can tell you who came to school today. It cannot tell you why someone stayed home. That fact was never written down.

A table can only answer questions whose answers are already inside it. There are three common ways a table falls short:

1. A missing column. The fact was never recorded (such as what Amara paid for her fruit).
2. Missing rows. The time, place or people you ask about are not in the table (such as last month).
3. A "why" question. Tables record what happened. They rarely record why.

Scope: what a dataset covers: which things (rows), which facts about them (columns), and which places and times.

If the answer is not in the rows and columns, no formula can find it.

See it done

Question: "Which fruit makes Amara the most profit?"

Data: market-stall-week.csv (synthetic).

1. Say what the answer needs. Profit is the money taken minus what the fruit cost Amara. So you need: quantity, the selling price, and the cost price.
2. Check the columns. quantity: yes. price_each_naira: yes. A cost column: no. Amara never wrote down what she paid.
3. Decide. This table cannot answer the profit question.
4. Say what it can answer instead. It can say which fruit brought in the most money (Watermelon, ₦77,000 this week), but money taken is not profit.
5. Say what is needed. "To work out profit, we need one more column: what Amara paid for one of each fruit."

The missing column is the problem. Better formulas cannot fix it.

Your turn, with help

"Did Amara sell more this week than last week?" Can her table answer this?

Hint: look at the dates. Which week does the table cover?

Your turn, alone

Can the table answer it? If not, say what is missing: a column, rows, or a "why".

1. (Amara) On which day did she take the most cash payments?
2. (Amara) Why do customers prefer oranges?
3. (Lucía) How many pupils in 5A have a dog?
4. (Lucía) How many pupils in 5B take more than 20 minutes to get to school?

Watch out

• Swapping in a near question. "Most money" is not "most profit". If you answer a nearby question, say clearly that it is different.
• Guessing to fill the gap. Never make up a cost or a reason to finish the job. Say what is missing.
• Stretching the scope. Amara's week tells you about her stall in that week. It does not tell you about every stall in Lagos, or about every week of the year.

Say it back

1. Name the three common reasons a table cannot answer a question.
2. Why can Amara's table not give profit?
3. What should you say when a table cannot answer a question?

What is next

That ends Module 3. You can now ask clear questions and answer them with sorting, filters and formulas. In Module 4, the numbers become pictures: bar charts and line charts, and how to read them correctly.