The One-Page Decision Memo

The memo is the product

Nobody at Alpenkorb will read Lena's queries. They will read one page and decide. A decision memo is short because its readers are busy, and it follows a fixed structure because a structure makes gaps visible. This lesson builds the last table and then writes the memo.

The last table: CAC by channel

The lab combines two small summaries for the first quarter of 2026: spend per channel from campaigns and new customers per channel from customers. A JOIN puts rows from two tables side by side where a key matches, here the channel name. Organic and direct visits have no spend, so they drop out. The result:

• Paid search: CHF 1,302.04 for 50 new customers, a CAC of CHF 26.04.
• Email: CHF 433.65 for 7 new customers, a CAC of CHF 61.95. Email mostly brings existing customers back, so CAC is the wrong yardstick for it.
• Affiliate: CHF 1,253.65 for 15 new customers, a CAC of CHF 83.58.
• Social: CHF 1,319.62 for 14 new customers, a CAC of CHF 94.26.

The structure

1. Decision          one sentence, with the deadline
2. Recommendation    what to do, in numbers
3. Evidence          three to five facts, each traceable to a query
4. Risks and limits  what could make this wrong
5. Next check        which number, when, and what would change the plan

• Put the recommendation before the evidence. Readers who agree can stop after two paragraphs.
• Give every number its unit and period: CHF 26.04 per new customer, first quarter of 2026, not 26.
• Leave out numbers that do not move the decision, however much work they took. A regional breakdown is interesting, but this budget is not regional.
• Write the limits yourself, before a reader finds them.

Lena's memo

Decision. How to split the second-quarter marketing budget of about CHF 4,300 across paid search, social, affiliate and email, decided by 15 April 2026.

Recommendation. Move about half of the social budget, roughly CHF 650, to paid search. Reduce affiliate spend by about a quarter by renegotiating commission terms. Keep email unchanged.

Evidence. In the first quarter of 2026 a new customer cost CHF 26.04 through paid search and CHF 94.26 through social. Of the customers won in 2025, 57.7 % from paid search ordered again, against 48.4 % from social and 39.7 % from affiliates. After the September push, social sessions more than doubled, while orders from social visits rose by about a fifth.

Risks and limits. CAC rises as paid search spend grows, because the cheapest searches are already bought; the extra CHF 650 will not bring 25 customers at CHF 26.04 each. Channel credit is last-click, so social may help more than it gets credit for. The analysis compares periods; it is not a controlled test.

Next check. Rebuild the CAC table at the end of May. If paid search CAC rises above CHF 60, stop shifting budget. Plan a controlled test of social ads for the third quarter.

This is the pattern of the whole program: a decision, a precise question, a few honest numbers and their limits. The following courses deepen each step, from KPI design and SQL to cohorts, attribution and experiments.