Imagine you have a spreadsheet with monthly stock returns for thousands of companies, plus details like size, valuation ratios, and past performance. The data is there, but how do you turn it into solid evidence about what drives returns? This chapter gives you the statistical tools to do just that. We’ll build a step‑by‑step method to summarize the data, measure relationships, build portfolios, and separate a strategy’s true return from the risk that just pays you for taking on more market exposure.