"This guide points to primary sources showing retail prices for common items or "necessities of life." Prices for foods, clothing, household items, fuels for heat and transportation, and fees for services fall within the domain of this guide. We also link to documents showing the average costs of major purchases such as houses, cars, and college education. Whenever possible, we point to retail price averages as reported in government publications. When those are not available, we point to prices appearing in other primary sources such as commercial trade catalogs, travel guides and newspapers. Because costs can only be understood within their historical context, we also point to primary sources showing average wages, salaries and earnings from colonial times to the present."