In part 4 of my series of posts about finding where it would be best to open up a pizza place in the US we looked at how we could use google trends data to measure interest for pizza across all the different states in the union. Today I want to address some of the potential biases in the above search by gathering more data related to large cities in the US. This will give us an idea about how state/city data compare and allow us to get a more complete picture of how the relative search interest of people in the US has evolved over time.
To build our database I used the pytrends library in the same way that I did in the previous post. However, instead of states, I used data for the top 100 cities by population in the US as given by wikipedia. I then did a massive general plot of the evolution of the relative search and its yearly moving average for all the 100 top cities (arranged by population above), showing the general trends in pizza searches (in this case the term in google trends was “Pizza in city”).
Search trends in cities match the trends we’ve observed for states. Almost all US cities have a decline in search interest related to the term “Pizza in city” when we consider the yearly moving average. For 89% of these cities we actually see a decline for the one year moving average from a year ago. The image below – which shows the change in the yearly moving average from one year ago to present – clearly shows this as well.
From the cities with the most positive change in interest the most positive is Saint Paul, in Minnesota, which has an increase of around 20% in the one year average during the past year. This is in great contrast with the worst city – St.Louis , Missouri – which has a drop of more than 25% in this same value. Increases in interest then decay sharply from Saint Paul, with the second and third cities being Norfolk, Virginia and Boise, Idaho (where I currently live!).
Even though the above might appear somewhat positive for these cities, a more detailed look at their charts shows that the evolution of their interest is actually not that positive overall but their recent increases have merely corresponded to mean reversions after falls in interest during the preceding years.
Looking at an all-time historical picture the overall dynamic also appears even darker with only 4 cities showing increases from 2016 to present in their yearly moving average, as shown in the last image above. In this last case we can see that the only 4 cities with an increase are Detroit, New York, Nashville and Chicago. All of them significantly touristic and two of them extremely well known for their pizza styles.
After looking at this data for google trends for relative search strengths for all US states and their cities, it’s starting to become clear that the general trend in very broad pizza searches is to the downside. It makes me think whether the question should be “where should I open my pizza place?” or “should I even open up a pizza place?”. This might be one of the instances where the data is asking us to reformulate the question since it might be showing that our initial assumption – that there might be an obvious and strong interest for pizza somewhere – might actually not be true.
There is of course the possibility that we’re reading too much into the data. For example real interest for pizza might not be directly related with google searches – people might go to pizza places they know about via word of mouth or that they see opening up – so we might want to look for data that is unrelated to what people search but that is instead related to what people experience. Social networks like twitter, might offer us some data to help navigate that hypothesis. I’ll look into this for my next post!