How is work-life balance measured? Is this self-reported data? What does the percentage mean?

From their website:

""" Life-work balance is an evolving definition, describing how we juggle our personal lives alongside the demands of our careers. Remote has coined the term to describe the increasing trend of people putting life first and work second.

Strong life-work balance extends beyond the ability to work from home. Measuring life-work balance with accuracy considers a number of the most important impacting factors ranging from payment rate to inclusivity. Putting Europe to the test, we conducted an index data analysis to reveal the top countries to live and work across the old continent. Would you consider a move abroad in search of a greater balance between your personal life and career?

The European Life-Work Balance Index assesses focuses on the countries situated in Europe, ranking the quality of life-work balance across each nation. The index considers a variety of vital factors including:

Healthcare
Minimum wage
Maternity leave
Statutory annual leave
Sick pay
Overall happiness levels 
Average working hours
LGBTQ+ inclusivity

"""

Kind of arbitrary set of data to be calling a work life balance index, but what do I know...