Cost Estimation Accuracy in Structural Engineering Projects Across Public Sector Institutions in Anambra State

Accurate cost estimation at the planning and design stages of structural engineering projects is fundamental to budget allocation, funding mobilisation, and contract award at realistic values in public sector infrastructure delivery. This study evaluates the accuracy of pre-contract cost estimates for structural engineering projects in public sector institutions in Anambra State in the South East geopolitical zone, examining eighteen bridge, culvert, institutional building, and drainage projects executed between 2020 and 2024. Final contract values and outturn costs were compared against pre-contract estimates produced at different design stages, and the estimation methods and data inputs used were examined through interviews with quantity surveyors and engineers in the Anambra State Ministry of Works. Cost estimation accuracy was measured using mean absolute percentage error and assessed against international benchmarks of less than fifteen percent for detailed design estimates. Results indicate that estimate accuracy deteriorated progressively with earlier estimation stages, with average mean absolute percentage errors of 48 percent for preliminary estimates, 31 percent for pre-tender estimates, and 22 percent for tender estimates. Key accuracy drivers identified were market price data recency, the quality of ground investigation data available at estimation time, and the estimator's familiarity with local labour and material rates. Estimates for bridge structures were significantly less accurate than those for building works, reflecting greater scope uncertainty in geotechnical and hydraulic design components. The study recommends an Anambra State cost data management system publishing quarterly updated unit rates, mandatory detailed design before tender for bridge projects, and professional quantity surveyor involvement from feasibility stage. Keywords: cost estimation, accuracy, public sector, Anambra State, structural engineering.