How do I know if this data is any good?

First, check out Where does the income data come from?

What the Census Bureau says about the American Community Survey: 

  • The American Community Survey (ACS) is on the leading edge of survey design, continuous improvement, and data quality
  • The nation’s most current, reliable, and accessible data source for local statistics on critical planning topics such as age, children, veterans, commuting, education, income, and employment
  • Surveys 3.5 million households and informs over $675 billion of Federal government spending each year
  • Visit 20,000 Group Quarter facilities and sample approximately 194,000 residents each year
  • Covers 35+ topics, supports over 300 evidence-based Federal government uses, and produces 11 billion estimates each year

One great feature of the American Community Survey data is that margins of error are included, so you'll know how confident you can be in the income estimates. Margins of error are + or - the estimate value. For example, Carbondale city, Illinois has a 2010 poverty percent estimate of 44.5% +/- 3.3%. Meaning, that the US Census Bureau is 90% confident that the poverty percent for Carbondale city, Illinois is between 41.2% and 47.8%.

You can find the margins of error in the "About the Data" section at the bottom of each zip code page on this website, and they are included in the zip code lists.