Think about all of the data those payroll tax payments must reflect:

* SSN or Individual Taxpayer ID Number (ITIN) of the worker
* Employer ID Number (EIN) of the firm paying the income
* an indication whether the pay involves hourly rates or salaried work
* an indication of hours worked (so state / federal governments can watch for OT violations)

Now you're getting into my area of professional expertise.

You are correct in that payroll tax payments are made very regularly by employers. Really big employers need to pay the payroll taxes the day after payroll is paid. Most other employers get a couple of days to pay the taxes. The very smallest can pay them monthly.

But there is no employee-level data in those payments. None at all. Not to the IRS. All the IRS sees is the amount of the payment, the employer's ID number, and the calendar quarter in which the payroll was paid. That's it.

At the state level, individual states might collect more information. I'm only intimately familiar with my home state, California. Here, the payroll tax payments are due on basically the same schedule as the federal tax payments. And, like the federal payments, contain no employee-level data.

Every quarter, California gets employee level data, but only name, SSN, and wages paid and state taxes withheld during the quarter. No hourly vs. salary. No hours worked. No overtime information.

California also has a new hire reporting system. Within a few days of hiring, the name and SSN of the new employee must be reported to the state. But that's it. (This reporting is used to help the state with tax and child support collections - so you can't avoid wage levies by moving employers. The state will catch up to you with a fresh levy within one or maybe two paychecks at most.) This information might help with new hire statistics. But there is no counterpart reporting for those leaving jobs.

The data your are assuming simply doesn't exist where it is accessible to nationwide statisticians. Hence the need for estimates.

--Peter