Which formula correctly calculates the percentage of time spent in N3 sleep?

Which formula correctly calculates the percentage of time spent in N3 sleep?

• A. minutes of N3 / TST × 100
• B. minutes of N3 / TRT × 100
• C. minutes of N3 / TST
• D. minutes of N3 × TST

Answer: (A)

To express what portion of sleep is in N3, you compare the time spent in N3 to the total time spent asleep, and then convert that to a percentage. The total sleep time (TST) is the sum of all sleep epochs during the recording, excluding wake periods. So, the proportion is minutes in N3 divided by TST, and you multiply by 100 to get a percent. Using total recording time would include wake time and distort the percent; omitting the ×100 would give just a fraction rather than a percentage. Therefore, minutes of N3 / TST × 100 is the correct formula.

To express what portion of sleep is in N3, you compare the time spent in N3 to the total time spent asleep, and then convert that to a percentage. The total sleep time (TST) is the sum of all sleep epochs during the recording, excluding wake periods. So, the proportion is minutes in N3 divided by TST, and you multiply by 100 to get a percent. Using total recording time would include wake time and distort the percent; omitting the ×100 would give just a fraction rather than a percentage. Therefore, minutes of N3 / TST × 100 is the correct formula.