Google Trends offers users highly up-to-date information on the relative popularity of a search. This is indicated by the inclusion of a score for the current month. This score is based on partial data, because the month is not yet complete and therefore, the data is not complete either.
Google Trends calculates all it's "interest over time" scores using the following steps:
- The actual search volume of each day within the time range is compared to the total number of search queries received by Google on the respective days. An average relative daily search volume is then worked out for each month or week.
- The month / week with the highest average relative daily search volume receives a score of 100. The scores of the remaining months are calculated relative to this.
In the case of "partial data", scores are based on an interim average relative daily search volume.
Google Trends tells us that it updates it's information daily. Thus, it is not 100% live. In most instances, the "partial data" score has taken into account search data up to 1 or 2 days before the Google Trends analysis has been conducted.
It is possible to determine precisely which days have been included in the calculation of a "partial data" month, by narrowing the Google Trends search to "past week". This will show which days have been awarded a Google Trends score and which days are yet to be assessed for scores.
For example, if you searched for "ice cream" on 20th April 2013, the score awarded for April 2013 would be based on the average daily search volume up to either 18th or 19th April 2013.
Any score based on partial data is capable of either rising or falling before the month completes.
Read more about partial data here: Understanding Google Trends