the challenges that are explicitly cited therein. This suggests room for growth in future research of project effectiveness.

As noted earlier, some of the findings explored may be endogenous, given that the project itself may have set about _ex ante_ to extend a loan or credit to address geographic barriers, remoteness, or the devastation wrought by a natural disaster. These features would specifically impact projects in certain sectors (such as transportation or agriculture). The positive effects might relate to improved project design attributes attached to those projects that address geographic isolation or natural disasters: their scope and objectives may be better defined and their deliverables more tightly focused than other comparable projects. In order to account for these idiosyncrasies, models were tested using both sector- and loan-type fixed effects, which would have captured any of the subgroup effects expressed here. Ultimately, the coefficients remained roughly consistent even with these indicators.

We conclude with an overview of the delivery challenges that most strongly impacted each outcome measure, as well as those that were consistently significant across measures. With respect to outcome ratings, changes in priorities, weaknesses in organizational capacity, and overambitious objectives (all related to project design or stakeholder engagement) consistently lowered outcome ratings, _ceteris paribus_ . Turning to Bank performance, we see that challenges related to project design (overambitious objectives) as well as those related to project data and monitoring yielded the greatest impact. The same appeared to be true for tests on the quality of supervision. Of the 42 individual challenges tested, four appeared to be consistently present in the model averaging runs. These were the quality of indicators, reporting and supervision, overambitious objectives, and organizational capacity. Given that all but the last were related to project design, we can conclude that the overall effectiveness of World Bank projects is to a great extent influenced by a set of factors established at the time the project is planned. Furthermore, it appears that these factors are relatively robust to variations in leadership, stakeholder relations, and context, posing a consistent risk to effective delivery across the portfolio of projects examined.

# **6** Conclusion

Can implementation-driven data on project challenges be used to holistically assess the effectiveness of World Bank lending? This paper took advantage of a wealth of practitioner experience captured in implementation completion reports as a granular and cross-comparable measure of project outcomes and Bank performance. Using a data-driven taxonomy, we devised a novel approach to examining the determinants of project success. By focusing on _how_ projects fail and the specific challenges faced in successful execution, we were able to capture variation hitherto unexplored in the aid effectiveness literature, offering a more precise assessment of the challenges faced throughout the implementation cycle while also providing a cross-cutting measure that reaches across the country-, time-, and sector- based approaches previously employed. Thus, while previous work offered insights into the individual mechanisms or contextual factors that might impact project effectiveness, we jointly tested the obstacles to success using a comprehensive analytic framework that allowed for the benchmarking of dozens of competing theories in a single unified model. Adjusting for alternate explanations and various contextual and structural preconditions, which components of implementation were most likely to impact project success?

Using project-level data from over 5,000 lending projects approved between 1995 and 2015, we tested this question using 42 specific delivery challenges across 14 overarching thematic categories. The 22