In 1984, only 13 states are labeled Ashley; by 1992, 30 states are. But it turns out that in 1984, a female baby born in the United States was actually 8 percent more likely to be named Ashley than in 1992.
Ashley was still the most popular girls’ name in 1991 and 1992. But its newfound dominance of the map is not the result of its growing popularity. Ashley was on the decline by the early ’90s—but other names were declining even faster. The original maps don’t actually say that Ashley was increasing in popularity in the early ’90s, but the way the information is presented, that misunderstanding is almost unavoidable. …
Again, this doesn’t mean the baby-name maps are wrong. They don’t purport to show anything except the most commonly given name in each state. In fact, these particular maps are well-designed and informative, if you have time to wade through the implications of the data. But it’s easy to see false trends here. Behind each map is data for hundreds of names across 50 states that would need to be examined closely to find the real trends. Unfortunately, there is no such thing as a viral Excel sheet.
But then he makes amends with an interactive feature displaying some maps of his own: