I have a few questions about patterns data. Visitor_home_cbgs is for each CBG, and visitor_home_aggregation is for each Census Tract, but if I add all cbgs' visitor's number in one Census Tract, it's not the same, I don't know why?

Hi, I’m Ryan from University at Buffalo. I have one question about pattern data, could you help me? visitor_home_cbgs is for each CBG, and visitor_home_aggregation is for each Census Tract, but if I add all cbgs’ visitor’s number in one Census Tract, it’s not the same, I don’t know why? Also, sometimes I find out that CBG has access data for this area, but Tract does not. Tract data contains CBG data, right?

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Hi @Ryan_Zhenqi_Zhou_SUNY_Buffalo ! If there is a census block group with only one visitor, that would not be reported in visitor_home_cbg for privacy reasons. However, it’s possible that the one visitor could be counted in visitor_home_aggregation if there’s another census block group in the same tract with 1 visitor (as 2 is above our privacy threshold). However, please note that in this situation it would appear as “4” due to our differential privacy policy. That’s why you might be seeing a disrepancy between the sum of visitor_home_cbgs and visitor_home_aggregation.

Note that we also add a jitter (Laplacian noise) to the two columns separately as an additional privacy measure. So it’s random noise first, and then the transformation that Niki describes above.

Thanks @Niki_Kaz @Eugene_Chong_SafeGraph , a lot of help~

No problem! To prevent any further questions from being overlooked, I’ll go ahead and close this thread out. If you have any more questions or follow-up questions, we’re always here to help! Just be sure to make a new post to help, as we aren’t monitoring old threads at this time. Thanks!