I are wondering two things. What is the difference the between “median_home_dwell_time” and “median_percentage_time_home” ? And, What is the difference between “candidate_device_count” versus “device_count”? Thanks!

Questions & Help
1

Hi All — — @James_Custer_UT_Austin and I are wondering two things.

  1. What is the difference the between “median_home_dwell_time” and “median_percentage_time_home” ? And,
  2. What is the difference between “candidate_device_count” versus “device_count”?
    Thanks!
2

hi @Paul_Rathouz_UT_Austin

did you read the documentation where these columns are defined?

If you are still confused, can you be more specific about your confusion? happy to help!

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So regarding “device_count” vs “candidate_device_count”, I am gathering that the former excludes devices without any activity in that time window. Correct? If so, what is “activity”? Thanks! looking again at the other two now.

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Regarding “median_home_dwell_time”, I am gathering this is the total number of minutes the device is detected at home during the time window. For “median_percentage_time_home”, I would have thought that is just the same thing, multiplied by (100/(24*60)). But, there is the clause “time we observed devices at home versus observed at all…” in the documentation. So, is the denominator different then 1440 minutes here?

5

@Paul_Rathouz_UT_Austin sorry for the delayed response.

You are correct about the difference between device_count and candidate_device_count

6

regarding dwell times

No, we do not observe devices every minute of every day.

A useful mental model is that we are getting a psuedorandom sampling of moments throughout the day for a device (“pings”).

Please see this discussion for more context.

https://safegraphcovid19.slack.com/archives/C0109NPA543/p1585778381343300

the percentage_time_home should be essentially time_home / (time_home + time_not_home)

But that denominator will almost never be 24 hours, because we are only able to receive data for a sampling of teh day.

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Please feel free to @ mention me if you have any additional questions