Google Health Application Programming Interface (API)

An API is a means of collecting data programmatically, allowing access to data that are difficult to collect by hand. The Google Health API was launched in 2009 to help researchers detect patterns in searches around the flu as a means for predicting its spread. For a given search term, the Google Health API gives researchers its relative share of all Google searches that were made by individuals within a defined geographic area and time range.


A request for data from the Google Health API that requires the user to specify one or more search terms, a time range, an interval and a geographic location.

Search string/search term

A set of words that people could search, e.g., “Flint water lead testing.” This study analyzed 2,693 terms in total, grouped into five search term categories.

Time range

The full period of time over which search trends are measured. This study covers Jan. 5, 2014, through July 2, 2016.


The length of time for which search data is aggregated (e.g., daily, weekly, monthly). This study looks at data measured on a weekly basis. Text referring to “the week of” a certain date always indicates the seven days beginning with that date.


A range of intervals (i.e. weeks), whose values are significantly different from the values of another period using changepoint models. See the section on the changepoint model used in this study for more information.

Geographic location

Restricts the results to searches that were made by individuals in a particular geographic region. This study looks at searches made in the whole United States, the state of Michigan and the Flint Designated Market Area (DMA).

Designated market area (DMA)

DMA stands for designated market area and it represents an exclusive geographic area of counties in which the home market television stations are estimated to have the largest audience share. Simply, a DMA is a geographic region in which a set of television and radio stations broadcast. In this study, when referring to search volume within Flint or the city, that represents the Flint DMA, which also includes surrounding counties.

Search activity or interest

The proportion of all Google searches within a defined geographic location and interval accounted for by a given search term or group of terms.

Google Health API sample

A sample is the result of one query to the Google Health API (term, time range, interval, location). It has one value per interval. For example, if we query the term “Flint water lead testing” for the time range of this study (01/05/2014–07/02/2016) by week, in the U.S., we get 130 values, each one giving the search volume for “Flint water lead testing” in the U.S. during that week.