robysue
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Posts: 1,247
Joined: Oct 2013
Machine: PR Dreamstation BiPAP Auto
Mask Type: Nasal pillows
Mask Make & Model: Swift FX
Humidifier: PR Dreamstation humidfier
CPAP Pressure: min EPAP = 4; max IPAP = 9;
CPAP Software: SleepyHead
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Location: Buffalo, NY

RE: Query on higher pressure
Folks,
In this thread the following statements have been made about mdh235's 95% pressure levels:
(07172014 06:57 PM)mdh235 Wrote: My apnea is totally controlled with a maximum pressure of around 12.6 (typical nights AHI .2 to .6). However, my machine seems to think the maximum pressure should be higher because my 95% number always equals my maximum pressure number, so I've been experimenting by raising the upper limit until my 95% value is always below it. For me, that's a setting of 14.
(07172014 09:40 PM)Sleepster Wrote: I don't understand. To me all this means is that you're spending 5% of the time at your maximum pressure, and that's successfully treating your apneas and hypopneas.
Is there an issue with your sleep quality? Like are you waking frequently or feeling tired during the day?
(07172014 09:52 PM)mdh235 Wrote: Perhaps I'm unclear about what the 95% number means. I thought it was the pressure that I spend 95% of the time at or below.
(07172014 10:15 PM)diamaunt Wrote: Quote:I don't understand. To me all this means is that you're spending 5% of the time at your maximum pressure, and that's successfully treating your apneas and hypopneas.
if the 95% pressure = max pressure, how do you get only 5% of the night at max?
(07182014 12:20 AM)Sleepster Wrote: Quote:Perhaps I'm unclear about what the 95% number means. I thought it was the pressure that I spend 95% of the time at or below.
Right, so you spend 5% of the time above that pressure. But as you said the 95% pressure equals the maximum pressure, so you are spending 5% of the time at your maximum pressure.
It's time for a basic statistics lesson folks.
First let's review of the statistical definition of 95% for a set of data: When we say the 95% of a data set is 10, that means that 95% of the data points are LESS THAN or EQUAL TO the number 10. And this also means that remaining 5% of the data points are GREATER THAN or EQUAL TO the number 10. But we can't conclude how many data points are equal to 10.
Consider the following sets of data, all of which have twenty points and all of which have a 95% equal to 10. In each list, the bold, italicized 10 is the 19th number on our list of numbers and since 0.95*20 = 19, this bold italicized 10 is the 95% for the set of data.
Data set 1:6, 6, 6, 6, 7, 7, 7, 7, 8, 8, 8, 8, 8, 9, 9, 9, 9, 9, 10, 11
Note that 95% of the data points are AT or BELOW the value 10. The remaining 5% of the data (the 20th data point) happens to be strictly GREATER THAN 10 in this particular case.
Note that we're AT the value 10 for exactly 5% of the night, we're BELOW 10 for 90% of the night, and we're ABOVE 10 for 5% of the night.
Data set 2:6, 6, 6, 6, 7, 7, 7, 7, 8, 8, 8, 9, 9, 9, 9, 10, 10, 10, 10, 11
Note that 95% of the data points are AT or BELOW the value 10. The remaining 5% of the data (the 20th data point) happens to be strictly GREATER THAN 10 in this particular case.
Note that we're AT the value 10 for exactly 20% of the night, we're BELOW 10 for 75% of the night, and we're ABOVE 10 for 5% of the night.
Data set 3:6, 6, 6, 6, 7, 7, 7, 7, 7, 8, 8, 8, 8, 9, 9, 9, 9, 9, 10, 10
Note that 95% of the data points are AT or BELOW the value 10. The remaining 5% of the data (the 20th data point) happens to be EQUAL to 10 in this particular case. So the remaining 5% of the data are GREATER THAN or EQUAL TO the 95% value.
Note that we're AT the value 10 for exactly 10% of the night, we're BELOW 10 for 90% of the night, and we're ABOVE 10 for 0% of the night.
Data set 46, 6, 6, 6, 7, 7, 7, 8, 8, 8, 8, 9, 9, 9, 9, 10, 10, 10, 10, 10
Note that 95% of the data points are AT or BELOW the value 10. The remaining 5% of the data (the 20th data point) happens to be EQUAL to 10 in this particular case. So the remaining 5% of the data are GREATER THAN or EQUAL TO the 95% value.
Note that we're AT the value 10 for exactly 25% of the night, we're BELOW 10 for 75% of the night, and we're ABOVE 10 for 0% of the night.
Data set 56, 7, 8, 9, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 11
Note that 95% of the data points are AT or BELOW the value 10. The remaining 5% of the data (the 20th data point) happens to be strictly GREATER THAN 10 in this particular case.
Note that we're AT the value 10 for exactly 75% of the night, we're BELOW 10 for 20% of the night, and we're ABOVE 10 for 5% of the night.
Data set 5 6, 7, 8, 9, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10
Since the bold, italicized 10 is the 19th number on our list of numbers and 0.95*20 = 19, this bold italicized 10 is the 95% for the set of data. 95% of the data points are AT or BELOW the value 10. The remaining 5% of the data (the 20th data point) happens to be EQUAL to 10 in this particular case. So the remaining 5% of the data are GREATER THAN or EQUAL TO the 95% value.
Note that we're AT the value 10 for exactly 80% of the night, we're BELOW 10 for 20% of the night, and we're ABOVE 10 for 0% of the night.
As these examples show, when the 95% = max value for a set of data, we can't conclude that we're at that max value for only 5% of the night.
A better way of thinking about 95% percentiles may be this:
You are AT or BELOW the 95% number for 95% of the time. And you are ABOVE the 95% for NO MORE THAN 5% of the time.
Questions about SleepyHead?
See my Guide to SleepyHead
(This post was last modified: 07182014 11:20 AM by robysue.)

