. 2021 Oct 5;11:19781. doi: 10.1038/s41598-021-99202-2

Table 2A.

Stepwise regression analysis in Experiment 1.

Experiment 1
Step 1: regression of Volume on pH (saving residuals to Res1)
Model: Volume = A + B * pH
Condition	R²		Coeff. value	Std. Error	95% confidence interval
Condition	R²		Coeff. value	Std. Error	Lower	Upper
Hypotonic 1.25%	0.630	A	34.06	8.75	15.91	52.20
Hypotonic 1.25%	0.630	B	11.02	1.74	7.42	14.62
Hypotonic 2.5%	0.970	A	19.16	2.43	14.13	24.20
Hypotonic 2.5%	0.970	B	14.84	0.54	13.72	15.96
Isotonic 1.25%	0.952	A	22.91	3.21	16.26	29.56
Isotonic 1.25%	0.952	B	11.67	0.55	10.54	12.80
Isotonic 2.5%	0.990	A	35.21	1.10	32.92	37.49
Isotonic 2.5%	0.990	B	9.71	0.21	9.28	10.13
Isotonic 3.75%	0.858	A	35.13	4.52	25.75	44.51
Isotonic 3.75%	0.858	B	11.89	1.00	9.80	13.97

Step 2: regression of Res1 on Osm
Model: Res1 = A + B * Osm
Condition	R²		Coeff. value	Std. Error	95% confidence interval
Condition	R²		Coeff. value	Std. Error	Lower	Upper
Hypotonic 1.25%	− 0.044	A	12.10	21.98	− 36.88	61.08
Hypotonic 1.25%	− 0.044	B	− 0.13	0.18	− 0.53	0.27
Hypotonic 2.5%	− 0.109	A	2.85	26.16	− 56.32	62.02
Hypotonic 2.5%	− 0.109	B	− 0.02	0.12	− 0.29	0.26
Isotonic 1.25%	0.720	A	− 72.69	13.31	− 102.35	− 43.03
Isotonic 1.25%	0.720	B	0.22	0.04	0.13	0.31
Isotonic 2.5%	− 0.095	A	3.67	18.30	− 37.11	44.45
Isotonic 2.5%	− 0.095	B	− 0.01	0.06	− 0.14	0.12
Isotonic 3.75%	0.422	A	− 124.18	45.24	− 224.98	− 23.38
Isotonic 3.75%	0.422	B	0.40	0.15	0.07	0.73

Multiple regression analysis was performed out in two steps. Firstly, a regression of Volume on pH was carried out, storing the residual in the variable Res1. Secondly, a regression was carried out of Res1 on Osm. For both analyses the R², coefficient value and standard error of the A and B coefficients are given as well as their 95% confidence interval. Note that the intercepts and slope coefficients (A and B) of the volume—pH relation show overlapping confidence intervals among conditions, indicating that the effect of pH on volume is similar in the different conditions.