Your story on how well or poorly American families fared in 2008 compared with 2007 is due shortly. You've completed all your interviews with selected families, and with two respected professors of economics. Income, not surprisingly, is the first issue you tackle. Here's where your hard facts come in. . .or so you think.
For your most important hard fact, you will cite data on income. But reviewing your notes, you see that one professor said families increased their income by nearly a thousand dollars during the year, while the other professor said household income declined during that time. Not only that, but the first professor said that 2008 income was over $67,000 per family, while the second maintained that, no, it was only around $52,000.
Both professors cited the same source: the U.S. Census Bureau.
Neither professor is wrong. The Bureau, rightly regarded as the gold standard in data collection on income and population, is also (in)famous for its blizzard of statistical reports, so many of which appear to present conflicting data, on the same subjects, for the same periods of time.
What does this mean to you, the journalist? It means you have to visit the Bureau to find the "correct" figure yourself. Not a daunting task, but it is essential that you pay close attention to the definitions the Bureau uses. For example, it makes a distinction between families and households. To confuse matters more, it has a separate definition for family group. And another for family households.
So in one report, Median Household Income in the Past 12 Months by State and Puerto Rico: 2007 and 2008, you will see that the estimate of median household income in 2008 was just as the second professor noted: $52,029, around six hundred dollars less than in the year before. But in another report, Median Income for 4-Person Families, by State, you'll find 2008 median income for this particular family composition just as the first professor said: $67,019, or some nine hundred dollars more than the previous year.
Further, one report uses fiscal years, the other calendar years.
There's really no rule of thumb regarding which figures to use. Most likely, your decision will reflect whether you want to show that we're worse off now, or better off. In other words, no matter how "objective" you think you are, to some extent the hard facts you choose to cite will reflect your subjective view. That's inevitable. If you wish to be honest, alert your readers to the differences between households and families (essentially, households may include people who are not related to each other). Full definitions are available at the Census Bureau site.
In the end, to maintain your integrity as a journalist, don't wave the flag of "objectivity." That term is a lot murkier than it appears.