## 4 Discussion  
### Proper Procedures for GPP  
An open procedure was tested to change oppositely with the possibility of a contract being green. Conversely, a green contract is more likely to apply other procedures, than open procedure. To estimate the correlation more precisely, we include a competitive dialogue, negotiation, and restricted procedure procedures into our regression. From Table 7, open procedure is no longer significant, as well as the negotiation without a call for competition. Competitive dialogue, negotiation with a call for competition, and restricted procedures all positively correlate with green contracts, having higher possibility than other procedures by 19%, 12%, and 10%, respectively. Other variables in the regression stay the same and statistical significance, signs and magnitudes of their coefficients barely change, compared with our main results (column (4) in Table 5).  
The results show that the most popular procedures used in green procurement is competitive dialogue followed with negotiation with a call for competition and restricted procedures. Competitive dialogue usually consists of a dialogue phase and a bidding phase, and in the former stage, public authorities can discuss the contracts with bidders. The input from economic operators can help the purchasing authorities to identify and organize proper requirements [24]. [PERSON], public procurement consultant of Rotterdam Municipality, said: _\"one important thing is that you have to have proper knowledge of what the market is able to deliver, which step the market is able to make\"_, in an interview with us in November 2019. The two-stage procedures--restricted procedures, competitive procedures with negotiation, and competitive dialogues [16] all increase information collection.  
Competitive dialogue can often occur in complex projects [25]. It is encouraged in the new directives for public procurement of EU that \"for services or supplies that require adaptation or design efforts, the use of a competitive procedure with negotiation or competitive dialogue is likely to be of value\" [16]. GPP involves the selection and weights of environmental criteria in technical  
\begin{table}
\begin{tabular}{c c c} \hline
**Procedures** & **Probit** & **Marginal Effect** \\ \hline Open procedure (OPE) & 0.21 & 0.046 \\  (0.15) & (0.032) \\ \hline Competitive dialogue (COD) & 0.88 *** & 0.19 *** \\  (0.23) & (0.05) \\ \hline Negotiation without a call for competition (NOC/NOP) & \(-\)0.024 & \(-\)0.0052 \\  (0.19) & (0.041) \\ \hline Negotiation with a call for competition (NIC/NIP) & 0.56 *** & 0.12 *** \\  (0.15) & (0.033) \\ \hline Restricted procedure & 0.48 *** & 0.10 *** \\  (0.16) & (0.034) \\ \hline Other variables in Equation (1) & Yes & Yes \\ \hline Country fixed term & Yes & Yes \\ \hline Month fixed term & Yes & Yes \\ \hline Observations & 16111 & 16111 \\ \hline Pseudo R2 & 0.2118 & – \\ \hline \end{tabular} Source: authors’ elaboration with Stata. Robust standard deviation is shown in the parentheses. *\(p<0.1\), **\(p<0.05\), ***\(p<0.01\).  
\end{table}
Table 7: Regression results on procedures. Dependent variable is “green contract”.  
specification, award criteria and contract clauses, which makes it complicated. It is reasonable to think that competitive dialogue and negotiation with a call for competition are trends in GPP projects, to guarantee the information symmetry between the environmental needs of governments and available access to the best solution in the market.