## 4 Results
Model 2 in Table 2 (Spain) presents a coefficient for \(\Delta lnSALE_{it}\) of 0.901 (\(p<0.01\)), indicating a positive and significant relationship between sales revenue changes and operating cost changes. The interaction term \(DEC_{it}\times\Delta lnSALE_{it}\) is \(-0.145\) (\(p<0.05\)), suggesting that operating costs in Spain do not decrease as significantly during periods of sales decline, indicative of cost stickiness. \begin{table}
\begin{tabular}{l c c c} \hline  & **Model 1** & **Model 2** & **Model 3** \\  & **(Whole Sample)** & **(Spain)** & **(Nordic Countries)** \\  & **(\(\Delta lnOC_{it}\))** & **(\(\Delta lnOC_{it}\))** & **(\(\Delta lnOC_{i}\))** \\ \hline \(\Delta lnSALE_{it}\) & 0.899 *** & 0.901 *** & 0.957 *** \\  & (30.527) & (38.286) & (18.0125) \\ \(DEC_{it}\times\Delta lnSALE_{it}\) & \(-0.153\) *** & \(-0.145\) *** & \(-0.339\) ** \\  & (\(-2.004\)) & (\(-2.557\)) & (\(-2.744\)) \\ \(SD_{it}\times DEC_{it}\times\Delta lnSALE_{it}\) & 0.110 ** & 0.124 ** & 0.132 ** \\  & (2.100) & (2.381) & (2.607) \\ \(lnDEBT_{it}\times DEC_{it}\times\Delta lnSALE_{it}\) & 0.101 ** & 0.151 ** & 0.117 ** \\  & (2.201) & (2.375) & (2.001) \\ \(SD_{it}\) & \(-0.001\) *** & \(-0.002\) *** & \(-0.0038\) *** \\  & (\(-4.591\)) & (\(-5.921\)) & (\(-6.833\)) \\ \(lnDEBT_{it}\) & 0.001 & 0.002 & \(-0.008\) \\  & (0.017) & (0.914) & (\(-1.291\)) \\ _Constant_ & \(-0.000\) & 0.002 & \(-0.001\) \\  & (\(-0.397\)) & (0.243) & (1.114) \\ \hline Year effects & Yes & Yes & Yes \\ Hansen test & 23.45 & 38.74 & 12.61 \\ m2 test & 0.88 & 0.77 & 0.67 \\ z1 test & 116.29 *** & 172.33 *** & 246.80 *** \\ z2 test & 5.21 *** & 4.97 *** & 10.31 *** \\ Observations & 683 & 575 & 108 \\ \hline \end{tabular}
\end{table} 
Table 2: Regression analysis. Model 3 in Table 2 (Nordic Countries), on the other hand, shows a more pronounced relationship with a \(\Delta lnSALE_{it}\) coefficient of 0.957 (\(p<0.01\)). The interaction term in this model is notably more negative at \(-0.339\) (\(p<0.05\)), suggesting a stronger presence of sticky costs in the Nordic region compared to Spain. This implies that operating costs in the Nordic countries are less likely to decrease in proportion to a reduction in sales, highlighting a more substantial effect of cost stickiness. Thus, when comparing the results of Models 2 and 3, it becomes evident that the Nordic countries exhibit higher levels of sticky costs than Spain. This is primarily evidenced by the more negative interaction term in the Nordic countries model, indicating that operating costs in this region are significantly less responsive to decreases in sales revenue. Regarding control variables, the coefficients for \(SDi_{t}\times DEC_{it}\times\Delta lnSALE_{it}\) in all three models are positive and significant and aligned with the findings of the previous literature [1; 81], suggesting managers view the downturn as more sustained following subsequent drops. The impact is slightly more pronounced in the Nordic countries. Likewise, the coefficients for \(DEBT_{it}\times DEC_{it}\times\Delta lnSALE_{it}\) are positive and significant in all models. This finding is consistent with earlier research, indicating a greater reduction in stickiness because of creditors' demands for a flexible cost structure to guarantee payments [81]. Remarkably, this effect is more pronounced in Spain than in the Nordic countries. Turning to the evaluation of the model's validity, the robustness of these findings is supported. The Hansen test, with null hypotheses positing the validity of the instruments, yields values of 23.45 for the whole sample, 38.74 for Spain, and 12.61 for the Nordic countries, indicating that we cannot reject the null hypothesis, and thus, the instruments are valid. Furthermore, the m2 test for second-order autocorrelation produces values of 0.88, 0.77, and 0.67, respectively, supporting the null hypothesis of no autocorrelation presence, affirming the absence of serial correlation issues in the error terms.