KPIs, Metrics and Vanity Numbers

Not every number deserves a meeting

Alpenkorb's data contains hundreds of possible numbers. Lena can put perhaps five in front of the management team. Three words help her choose.

• A metric is any measured number: sessions, clicks, orders, average order value.
• A KPI, key performance indicator, is a metric tied to a goal and a decision. If it moves, someone acts.
• A vanity number grows easily, looks good on a slide and changes no decision. Impressions, followers and raw sessions are the usual suspects.

The same metric can be a KPI in one decision and vanity in another. Sessions are a KPI for the team that keeps the website fast. For a budget decision they are vanity, because a franc that buys a visit which never orders is simply spent.

The cheap click trap

In the first quarter of 2026 social ads cost CHF 1,319.62 and produced 1,390 clicks, about CHF 0.95 per click. Paid search cost CHF 1,302.04 for 792 clicks, about CHF 1.64 per click. Social also brought more sessions than any other source, 1,028 against 670 from paid search. On the numbers most ad platforms show first, social wins.

The trap works because clicks are real and measured precisely. Precision is not relevance: a number can be exact to the Rappen and still answer the wrong question.

The KPI that matches Lena's decision is customer acquisition cost, CAC: the spend on a channel divided by the new customers it brought in the same period. Spend is in the campaigns table, one row per channel and month. New customers are in the customers table, where signup_date is the day of the first order and acquisition_source is the source of that visit.

SELECT channel,
       ROUND(SUM(spend_chf), 2) AS spend
FROM campaigns
WHERE month >= '2026-01-01'
  AND month < '2026-04-01'
GROUP BY channel;

Paid search brought 50 new customers in the quarter and social 14. That gives a CAC of CHF 26.04 for paid search and CHF 94.26 for social. Social had cheaper clicks, yet each new customer cost more than three times as much. The GROUP BY above returns one row per channel; lesson 6 explains how it works, and lesson 8 builds the full CAC table.

For her memo Lena sorts the numbers into three groups. Her KPIs are CAC per channel and the share of new customers who order again. Supporting metrics, shown only to explain the KPIs, are spend, sessions and conversion by source. Impressions, clicks and follower counts stay out of the memo, not because they are false, but because no budget choice follows from them. If a reader asks for them, they can go in an appendix.

Four properties of a good KPI

• It is tied to a decision that someone owns.
• It has an exact definition: which rows, which period, which formula.
• It can be compared over time, between channels or against a target.
• It is hard to game. Clicks can be bought cheaply; paying customers cannot.