Why does the processing time for the N-400 Application for Naturalization Form vary so much within the same USCIS field office?

Question

I read that the processing time for the N-400 Application for Naturalization Form varies a lot within the same USCIS field office. The processing time the 93% slowest application is quite higher than the median processing time, sometimes even more than double. That's a rather long tail distribution instead of a narrow gaussian that I was expecting. Why does the processing time for the N-400 Application for Naturalization Form vary so much within the same USCIS field office? Which factors in the N400 impact the processing time?

E.g., for Spokane in Washington, the processing time the 93% slowest application (19.5 months) is more than double the median processing time (8 months).

Answer 1

These applications are adjudicated on a case by case basis. Some cases are trivial, some are less so. Some require more background information, some require investigation into the past of the applicant, some require waiting for additional information to come from other sources (including external to the US), etc.

I'll give you some examples:

• Applicant got their green card through marriage, but filing N-400 as divorced. What happened? Was it a sham marriage?
• Applicant got their green card through employment as an engineer, but are applying for naturalization as an Uber driver. Did they lie?
• Applicant applies for naturalization, but their declared days of stay don't match their I-94 records. Did they make a mistake? Did the CBP make a mistake? Are they trying to lie?
• Applicant applies for naturalization but apparently "forgot" to file their taxes for 5 years. Now we wait for them to file.

Etc etc.

Answer 2

Reddit user boredlurker87 mentioned describes the N-400 application processing as follows:

It is mostly an electronic workflow. When you submit the application online (and it’s true even for paper based, application is converted to online at FO), your A number is automatically validated, then scheduling/reusing biometrics and security checks happen automatically. Results are sent back to ELIS automatically and placed in file. If there’s an issue in security checks it’s placed in an officer queue for reconciling. Once everything is available, it is placed in queue for interview at the FO. The FO supplies dates, availabilities among other things to NBC and the interview is scheduled. The review occurs when the file is sent to the FO prior to the interview… other than that it’s pretty much an all-electronic workflow for preprocessing.

As a result, issues during the security checks could be one explanation of why the processing times for the N-400 Application for Naturalization Form vary so much within the same USCIS field office.

Reddit user prettyeye28 added the following (albeit no specific to N-400):

In my office there is no visibility [into who and how puts those files in shelf and in what order]. A box (or several) are emptied onto the shelf. And then we officers grab. Right now there are way too many files for the records section to look at the dates and put them on the shelf that way.

https://redd.it/vnonem seems to say the USCIS sometimes process cases out of order too (the screenshot was taken on https://hilites.today/):