Table 1. Logistic regression model for probability of detecting at least one orang-utan on an expedition.

	Estimate	Std. Error	z value	Pr(>|z|)
Intercept Model 1a	18.41009	16.85967	1.092	0.27485
Intercept Model 1b	26.636752	17.933663	1.485	0.13747
Year Model 1a	−0.01174	0.00852	−1.378	0.16820
Year Model 1b	−0.015438	0.009071	−1.702	0.08879
Person Model 1a	0.02789	0.06676	0.418	0.67605
Person Model 1b	−0.164621	0.125249	−1.314	0.18873
log(Days) Model 1a	1.92088	0.63607	3.020	0.00253 **
log(Days) Model 1b	1.965192	0.639650	3.072	0.00212 **

Model 1a includes the 33 person expedition. Model 1b excludes 33 person expedition. Year = year in which expedition was conducted. Person = number of people on an expedition. Log(Days) = natural logarithm of duration of expedition in days. Significance code: ‘**’: p<0.01.