One way to approximate each professional sport league’s relative popularity is to look at web search trends over time. Google Trends simplifies this task tremendously by reporting the relative frequency by which certain words or phrase are entered into Google’s search engine.
The chart below plots the raw data from Google Trends for the five major sports leagues in the United States: NBA, NFL, NHL, MLB, and MLS. The seasonal nature of these sports means that search frequencies vary dramatically over the course of each year, making graphical comparisons somewhat difficult without further analysis.
To make the above series more usable, we can remove seasonality from the series in a process called time series decomposition. This process splits a time series into the following three components: (i) seasonal, (ii) trend, (iii) random noise. Depending on the data, seasonal trends are determined by summarizing patterns that occur yearly, monthly, or weekly. In the present case, we have weekly data from 2004 – 2013, which means that a particular week in any year should bear a resemblance to that same week in the remaining years. For example, the first week of 2004 should be similar to the first week of 2005, 2006, etc. The second component (the trend) is computed using a series of several local regressions called a loess procedure. Finally, the random noise is calculated by subtracting the seasonal and trend components from the original time series. For comparative purposes hear, we ignore the random noise since it only distracts from the underlying trend.
The chart below shows (i) NBA searches, (ii) seasonally adjusted NBA searches (calculated by subtracting the seasonal component from the original series), and (iii) the underlying trend of NBA searches.
The blue line above makes discerning the underlying trend significantly easier. For that reason, I plot the underlying trends for each of the five sports leagues below.
The plot above is much more usable because the underlying trends are readily apparent. NBA and NFL searches are higher than the other sports and have generally increased considerably during the period under review. MLB and NHL searches are less common and relatively consistent with some fluctuations. MLS, which is often described as growing in popularity, is the only league with markedly decreasing searches.