Module 5 · Data Analyst Capstone: End-to-End BI Project
Analyse
Answer the chief executive's questions one by one, separate real growth from price and new stores, find what's going wrong where, and put a naira value on missed sales.
About 30 minutes
The problem
The board is celebrating 37% growth. Your job now is to find out what's underneath it. A headline number like that almost always mixes several stories, some good and some bad, and the bad ones are easy to miss when the total looks healthy.
This lesson works through the plan from lesson 1. For each question you'll get a number, check it, and write down what it means. Those notes become your executive summary in lesson 6.
The concept
Decompose the headline
Revenue growth = price + new stores + everything else (volume and mix in the existing stores). Separate them:
- New stores: compare like for like, leaving out stores not open in both periods (Lekki).
- Price: compare the like-for-like growth with the 18% price rise. Whatever's left is real change in volume or mix.
Compare like with like, then look inside
For each store, compare January to June 2026 with January to June 2025: sales, transactions and average transaction value. When something changes sharply, find the date it changed. A step change on a particular date usually has a specific cause.
Look for money left on the table
| Leak | Measure |
|---|---|
| Missed add-on sales | Attach rate: the share of phone transactions that include an accessory |
| Returns | Return rate: units returned ÷ units sold, by product |
| Stock-outs | Lost sales estimate: normal daily sales × days out of stock × price |
Every estimate needs its assumptions
A lost-sales figure is an estimate, not a fact. Say how you made it: which period you took as "normal", how many days, which price, and what you ignored (customers who bought a different model instead, for example). An estimate with clear assumptions is useful; one without them isn't trusted.
Example
The growth, decomposed, for January to June:
| H1 2025 (₦m) | H1 2026 (₦m) | Growth | |
|---|---|---|---|
| All stores | 1,551.9 | 2,133.2 | +37.5% |
| Like for like (excluding Lekki) | 1,551.9 | 1,835.2 | +18.3% |
| Lekki (opened July 2025) | 0 | 298.0 |
Prices rose 18% in January 2026. Like-for-like growth of 18.3% means the existing stores sold almost exactly the same volume as a year earlier. The real growth story is one new store and a price rise. That's not a disaster, but it's not what the board thinks either.
Walkthrough
- Reproduce the decomposition above in your tool, and check that Lekki plus like for like adds up to the total.
- Build a table of each store's H1 2025 and H1 2026 net sales and transactions (sales transactions only, not returns). Which store stands out?
- For that store, plot weekly transactions over the whole period. Find the month the change starts, then check with the business. (When you ask, Voltline's regional manager tells you a competitor opened next door in February 2026. In a real project, that conversation is part of the analysis.)
- Calculate the attach rate for each store: among transactions that include a phone, the share that also include an accessory.
- Calculate the return rate for each product. One stands far above the rest.
- Use
stockouts.csvto estimate lost sales for the Wuse 5kVA inverter stock-out (the task below). - For each finding, write one sentence: the number, and what it means.
Practice
Practice
What was like-for-like net sales growth, January to June 2026 against January to June 2025, excluding Lekki? One decimal place.
Practice
At Port Harcourt, by how much did the number of sales transactions (excluding returns) change between February–June 2025 and February–June 2026? One decimal place (it's negative).
Practice
What is Garki's accessory attach rate: the share of its phone transactions that also include an accessory, across the whole period? One decimal place.
Practice
What is the return rate (units returned ÷ units sold) of the Zentro Z5 64GB (VP-101)? One decimal place.
Task
10 minEstimate the sales lost while Wuse was out of stock of the Inverter 5kVA (VP-403), from 2 March to 23 April 2026. Give your method, your assumptions and the estimate in naira, in a short paragraph or a few bullets.
Your work is checked for
- Gives the number of days out of stock
- Uses a normal sales rate (per day, week or month) from a period before the stock-out
- States at least one assumption
- Gives an estimate in naira
- Mentions price or margin
- Enough detail: at least 50 words
Check your understanding
Answer every question to check.