Review questions
Integrated Summary: From a Business Question to Trustworthy Data and Metrics
Business data analysis starts before any tool is opened. The sound starting point is the business need and the decision that could change because of the result, then an analytical question that available data can answer. “Performance is poor” is a broad symptom. “How did order completion proportion and average order value change from Q1 to Q2 by region and customer type?” defines measures, a period and segments. If the task is to estimate a campaign effect but there is no exposure variable, do not invent one or call a descriptive change an “effect.” Answer what the data support and record the measurement gap.
Once the question is framed, understand what the data represent. A data source tells where values came from, the unit of observation tells what a row represents, and grain states the finest stored level. This matters when joining tables. In a synthetic example, three orders have values 100, 60 and 140, so the correct total is 300. After a one-to-many join from orders to order lines, order values can repeat on each line and produce the incorrect total 680. The formula did not fail; row grain changed. Therefore define keys and relationships, use a data dictionary that explains meaning, type, unit, allowed values and derivation rules, and keep simple lineage from source through transformations.
A metric is a definition before it is a number. A good metric card states numerator, denominator, period, segment, inclusion/exclusion rules and source when relevant. 930 on-time completions out of 1,200 eligible orders gives 77.5%. If the previous period was 74.0%, the direct change is 3.5 percentage points, while relative change is about 4.73%. Confusing the two changes the message. A metric becomes a KPI when it is tied to an objective, decision, monitoring and responsibility; a fictional teaching target is not a universal benchmark. Denominator stability matters as much as the metric label.
Next, assess data quality in relation to intended use. The six dimensions used in this subject are completeness, uniqueness, consistency, timeliness, validity and accuracy. Keep them distinct. In a synthetic dataset, 97 unique records remain after three confirmed reload duplicates are removed, and channel is missing in 8 records. Completeness is therefore 89/97, about 91.8%. Negative quantity values are a separate validity issue, not a completeness issue. Missing does not mean zero, an apparent duplicate should not be deleted before understanding grain, and an outlier is not an error merely because it is far from other values.
Good cleaning is traceable: preserve a path back to source and record the rule, affected count, action, rationale and analytical effect. Quality dimensions can also trade off. A rapid report may be more timely but less fully verified. The right choice depends on the decision purpose and cost of error, and provisional status and completeness should be disclosed. The four lessons therefore form one chain: a bounded question, data understood at the correct grain, a precisely defined metric, and documented quality processing. If any link fails, the calculations can look polished while answering the wrong business decision.
Review questions
Test your understanding with these questions. Marking and saved results are available with a free account.
Create a free account to mark your answers and save your progress.