reading forbes 400 about airbnb founders. the context is the following:
The airbnb founders’ net worths are down versus a year ago because Forbes is using a lower estimate of their ownership stakes.
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Sign up to join this communitySince an estimate is an educated guess or calculated approximation of some metric, such a calculation will be bounded by upper & lower values based on the range of possible values for some parameters which affect the result.
Therefore, in your quote, the phrase "Forbes is using a lower estimate" essentially means that they are using an estimate at the lower end of the possible forecasted outcomes which have been calculated from the available data. Some might describe this as a 'conservative estimate'.