Clean Spreadsheet Data Before You Analyze It

Analysis can only be as dependable as the data underneath it. A clean spreadsheet has one clear meaning per column, consistent formats, and enough context for someone else to understand how the information was collected.

Keep one type of value per column

Store dates as dates, amounts as numbers, and notes in a separate field. Avoid entering a currency symbol or extra text into numeric cells when you need to calculate them. Use one spelling for each status and one unit for each measurement. A short data dictionary can explain labels that are not obvious.

Check common sources of noise

• Look for duplicate records using a stable identifier.
• Find leading or trailing spaces in names and categories.
• Check whether blank cells mean unknown, not applicable, or zero.
• Review date ranges, unexpected negative values, and inconsistent units.

Preserve the source

Keep an untouched copy of imported data and perform cleanup in a separate table or version. Record the transformations you made, especially when merging categories or removing rows. This makes it possible to repeat the process and investigate a surprising result.

Before sharing an analysis, verify a few records against the original source and explain important limitations. Clean data does not guarantee a correct conclusion, but it makes errors easier to catch and work easier to trust.