"confidential level" is correct and usable in written English.
You can use it when you are discussing a certain level of secrecy, such as revealing information about something to a select group of people who are not supposed to share it with anyone else. For example: "We discussed top secret plans in a confidential level meeting."
Nearly all of the emails were classified by the State Department at the "confidential" level, the lowest level of sensitivity, but 44 were classified at the "secret" level.
After going through the e-mails they uncovered that weren't handed over to the State Department, the F.B.I. determined that three of them contained classified information — one at the "secret" level and two at the "confidential" level.
For a confidential level of 90%, pH showed a low effect on the initial degradation rate of alachlor; whereas electrical power, pollutant concentration and the interaction of these two parameters were significant.
The agent wrote that the government had determined 2,115 emails on the Clinton server were classified — 2,028 at the confidential level, 65 at the secret level and 22 at the top secret level, which is the most sensitive.
Finally, the scale factor τ could be obtained through statistical analysis to the elements of R which makes the totals of R satisfy a certain confidential level, say 95%, and not greater than τ.
The State Department has designated 1,582 of Clinton's emails classified and almost all has been classified at the "confidential" level.
In late December, he said, the state department told Linick's office that 12 out of 19 documents under review "contain national security information classified at the Secret or Confidential levels based on a review by nine department bureaus and office".
In fact an internal investigation revealed that, "the State Department found that emails handled on private email accounts associated with Colin Powell and Condoleezza Rice contain "information classified at the Secret or Confidential levels.'" Yet only Clinton is singled out for this practice in an astonishing demonstration of double standards.
The FBI's memorandum said that dozens of emails Clinton received from her unofficial adviser and close confidante, Sidney Blumenthal, were determined to contain information at the confidential and secret level.
With respect to the thousands of emails we found that were not among those produced to State, agencies have concluded that three of those were classified at the time they were sent or received, one at the Secret level and two at the 'confidential' level.
This is similar to the previous section, which states the F-statistics are significant in the 10% confidential interval level for all the 39 regressions and there is no significant autocorrelation for the errors of 39 regressions.
