What Google Trends Tells Us:
Google Trends tells us that its scores are based on an analysis of a portion of search volume. This means the scores are only based on a sample of available data, rather than all available data.
How are Interest Over Time Scores Calculated?:
Google Trends tells us that it scores are relative. An “interest over time” score for any particular day / week / month is awarded on the basis of its actual search volume relative to the actual search volume of the other days / weeks / months. A score of 100 is always awarded to the day / week / month with the highest relative search volume, with the other days/ weeks / months scaled between 0 and 100 accordingly.
When a term is analysed over time within global parameters the scores are calculated using an average score (based on the scores returned from each country). This prevents search terms with high popularity in countries with heavy internet usage constantly achieving high scores.
How are Regional Interest Scores Calculated?:
In the case of “regional interest” scores, Google Trends uses relativity in order to prevent countries with high internet usage automatically receiving the highest scores. The scores are calculated by comparing the relative popularity of the search term within each region. This data is then scaled between 0 and 100, with the country with the highest relative interest receiving a score of 100.
How Broad is the Search Volume Data Used to Calculate Scores?:
Google Trends offers users the ability to search for an exact phrase by enclosing it in quotation marks. According to the Help Centre when this function is used, scores generated are based on "specific order" search volume. This means that data from searches that include the inputted search terms in the specific order they have been entered will be used. No synonyms or variations are considered.
Google Trends also states that where no "quotation marks" are used, results include searches for the inputted terms in any order and may also include extra terms. No synonyms or variations are considered.