The initial model and two refinements are shown in Table 1.

Table 1.  Multiple linear regression models.

Model

Adjusted-R2

F

p-val

Predictor 1 (transform)

p-val

Predictor 2

/transform

p-val

Predictor 3

/transform

p-val

1

0.6341

<0.05

latitude (none)

0.20

winter_temp (none)

<0.05

winter_prcp (log)

<0.05

2

0.6306

<0.05

winter_temp (none)

<0.05

winter_prcp (log)

<0.05

none


3

0.6052*

<0.05

winter_temp (none)

<0.05

winter_prcp (log)

<0.05

none


*Model 3 used a reciprocal transformation on t, see the residual normal Q-Q plot in Figure 1.