The score is a calculation over a researcher's data giving an overall score on the completeness of the data. The goal is that seeing this number go up will encourage you to fill in gaps in your current data, and to keep it filled in with new entries.
The score is calculated based on the number of a researcher's records that have
So if everyone of in a branch has a first name, last name, birth date & place, death date & place, the score will be 100%, or higher if there are enough bonus points added. The score is then shown in the form of gold stars with 4 starts being 100%. Remember getting gold stars for being a good kid? Here's your chance again.
Tip: For anyone living in the US 1850-1920, birth dates and states can usually be found in the census. For anyone who had children living 1880-1920, the parents' birth states can be found in their children's census.