Results
The mean value of PNIF for this series of 79 patients was 92.6 l/min (SD 28.1 l/min). The mean NOSE score for this group of patients was 48.4 (SD 24.4). The boxplots for these values are displayed in Figure 1 and in Figure 2, respectively.
The scatter plot and the simple regression line of best fit together with 95% confidence bands are shown in Figure 3. It can be observed that there is a decrease in NOSE scores as PNIF values increase, showing a negative correlation. This correlation is statistically significant (p =0.03). The multiple linear regression model demonstrated that for an increase of one unit in NOSE score, PNIF decreases on average 0.25l/min, 95% CI (-0.51, 0.008) p=0.057, when adjusting for age and gender (Table 1). The estimated correlation coefficient between NOSE score and PNIF value was found to be -0.248, which demonstrates a weak association between PNIF value and NOSE score in the group of 79 patients.
In the groups allotted by the NOSE score, the scatter plot and the simple regression line of best fit together with 95% confidence bands are shown in Figure 4. The estimated correlation coefficient for the group of 24 patients with a NOSE score equal to or less than 35 was found to be -0.250, which demonstrates a weak association between PNIF value and NOSE score. In the group of 26 patients with a NOSE score between 36 and 64 the coefficient of correlation between PNIF and NOSE demonstrated a very weak association (r =-0.007). The estimated correlation coefficient for the group of 29 patients with a NOSE score equal to or higher than 65 was found to be -0.104, which demonstrates a very weak association between PNIF value and NOSE score.
In the groups allotted by the PNIF value, the scatter plot and the simple regression line of best fit together with 95% confidence bands are shown in Figure 5.
The estimated correlation coefficient for the group of 20 patients with a PNIF value equal to or less than 70 l/min was found to be -0.404, which demonstrates a moderate association between PNIF value and NOSE score. The estimated correlation coefficient for the group of 39 patients with a PNIF value between 71 l/min and 109 l/min was found to be -0.190, which demonstrates a very weak association between PNIF value and NOSE score. In the group of 20 patients with a PNIF value equal to or higher than 110 l/min there was a very weak association between PNIF value and NOSE score (r =-0.014).