Analysis of flexyble pavements using the multilayered elastic theory involves the use of elastic moduli backcalculated from deflection basins meansured utilizing the Falling Weight Deflectometer (FWD). Uncertainties associated with the thickness of the studied to increase the reability and accurancy of the backcalculated deflection basin by minimizing the relative root-mean-square error (RMSE). Therefore, the RMSE of the backcalculated set of elastic moduli of pavement. In this study, the sensitiveity of the pavement response to the RMSE less than 1%. The results showed that even when the RMSE in the deflections is as low as 0.22%, the pavement response (strain, stress, and therefore fatigue and rutting predictions) using the backcalculated set of moduli can largely be different than that using the exact set of moduli, suggesting more uncertainties to the backcalculated set of moduli.