Our work on the Bureau’s 2010 Census life-cycle cost estimate found that it was not reliable, because it lacked adequate documentation and was not comprehensive, accurate, or credible. For example, in our 2008 report on the Bureau’s cost estimation process, Bureau officials were unable to provide documentation that supported the assumptions for the initial 2001 life-cycle cost estimate as well as the updates. We reported that without improvements to the cost estimation process, the Bureau's ability to effectively manage operations would be hampered and Congress's ability to oversee the 2010 Census would be constrained. Consequently, we recommended that the Bureau establish guidance, policies, and procedures for conducting cost estimation that would meet best practices criteria. The Bureau agreed with the recommendation and said at the time that it already had efforts underway to improve its future cost estimation methods and systems. Moreover, weaknesses in the life-cycle cost estimate were one reason we designated the 2010 Census a GAO High Risk Area in 2008. Bureau officials stated they have been working toward implementing the standards of our Cost Estimating and Assessment Guide since 2008. However, in a 2012 report, we found that while the Bureau was taking steps to strengthen its life-cycle cost estimates, it had not yet established guidance for developing cost estimates, and we recommended that the Bureau finalize its guidance, policies, and procedures for cost estimation in accordance with best practices. In its response to that report the Bureau agreed with the overall theme of the report, but did not directly comment on that recommendation, which remains open, as discussed later in this report. To help control costs while maintaining accuracy, the Census Bureau is introducing significant change to how it conducts the decennial census in 2020. Its planned innovations include reengineering how it builds its address list, improving self-response by encouraging the use of the Internet and telephone, using administrative records to reduce field work, and reengineering field operations using technology to reduce manual effort and improve productivity. The Bureau estimates that if it succeeds with these innovations it can conduct the 2020 Census for $12.5 billion in constant 2020 dollars. By contrast, the 2020 Census would cost $17.8 billion in constant 2020 dollars if the Bureau repeats the 2010 Census design and methods, according to the Bureau’s estimates. Major innovation does not come without risks and in order to manage and mitigate them the Bureau has established a decennial risk management process governing two types of risks: project risks and program risks. The Bureau defines project risks as those that could jeopardize success of an individual project, such as the Bureau's operation to collect responses door-to-door from households that do not respond to Bureau mailings. The Bureau defines broader program risks as those that jeopardize the success of the 2020 Census program, typically spanning several years with many potential risk events over the period. These may have elevated from project level risks and include risks such as the possibility that external stakeholders do not support the planned design changes. As early as 2011, the Bureau began developing preliminary cost estimates of the 2020 Census in order to approximate potential savings from its plans to reengineer the census, and, according to the Bureau, to begin developing the methodology for producing the decennial life-cycle cost estimates. The Bureau’s October 2015 release of the latest cost estimate marked the transition from the “research” to “implementation” phases of the 2020 Census. According to the Bureau, this was the Bureau’s first attempt to model the life-cycle cost of its planned 2020 Census, in contrast to its earlier 2011 estimate which the Bureau said was intended to produce an approximation of potential savings and to begin developing the methodology for producing decennial life-cycle cost estimates covering all phases of the decennial life cycle (see fig. 1). According to Bureau officials, they recently implemented a software upgrade they believe has better positioned them to deliver a quality cost estimate. They stated that they relied primarily on a cost estimation team of five individuals in the Decennial Programs Directorate to develop the 2020 Census life-cycle cost estimate. This team drew in part on subject matter specialists involved in the Bureau’s research and testing of its planned innovations in order to help develop a cost model and to obtain data to inform key assumptions within the model. The specialists typically provided the cost estimation team with data on each assumption using a three-point method, whereby the cost estimation team received a “minimum,” “value,” and “maximum” input for each assumption, representing whatever uncertainty or risks the provider had considered. Figure 2 shows the Bureau’s cost estimation process. Because cost estimates predict future program costs, uncertainty is always associated with them. For example, data from the past (such as fuel prices) may not always be relevant in the future. Risk and uncertainty refer to the fact that because a cost estimate is a forecast, there is always a chance that the actual cost will differ from the estimate. One way to determine whether a program is realistically budgeted is to perform an uncertainty analysis, so that the probability associated with achieving its point estimate can be determined, usually relying on simulations such as those of Monte Carlo methods. This can be particularly useful in portraying the uncertainty implications of various cost estimates. Consistent with prevailing cost estimation practices, the Bureau’s Office of Cost Estimation, Analysis, and Assessment (OCEAA), in the Deputy Director’s Office (see fig. 3), began generating an independent cost estimate in fiscal year 2015, and shared it with the cost estimation team in April 2016. OCEAA and the cost estimate team worked together to examine the process they each used, an effort known as the reconciliation process. According to Bureau officials, reconciliation is a major step in the cost estimation process, and it may help identify areas of improvement for the Bureau’s cost estimation process. Officials also said that this reconciliation was to be shared with the Department of Commerce in June 2016 as part of its 2020 Census budget process. The Bureau plans annual updates of its cost estimate, leaving three updates before the Bureau begins implementing its earliest operations in 2019 for the 2020 Census. Since our January 2012 report in which we reviewed the Bureau’s initial estimate of the total cost of the decennial census, the Bureau has taken significant steps to improve its capacity for cost estimating. For example, the Bureau established OCEAA as an enterprise-level cost estimation office and hired certified cost analysts. Despite this progress, the Bureau’s October 2015 cost estimate for the 2020 Census does not fully reflect characteristics of a high-quality estimate as described in our 2009 Cost Estimating and Assessment Guide and cannot be considered reliable. A reliable cost estimate is critical to the success of any program. Such an estimate provides the basis for realistic budget formulation and program resourcing, meaningful progress measurement, proactive course correction when warranted, and accountability for results. According to the Office of Management and Budget (OMB), programs must maintain current and well-documented estimates of program costs, and these estimates must encompass the full life-cycle of the program. Without this capability, agencies are at risk of experiencing program cost overruns, missed deadlines, and performance shortfalls. The Cost Estimating and Assessment Guide describes best practices for the development of reliable cost estimates. For our reporting needs, in the cost guide we collapsed these best practices into four general characteristics for sound cost estimating—comprehensive, well-documented, accurate, and credible—and identified specific best practices for each characteristic. To reflect these characteristics, an organization must meet or substantially meet each best practice. Our review found the Bureau partially or minimally met the cost estimating best practices. More specifically, it partially met two characteristics and minimally met two characteristics (see table 1). According to our best practices, an estimate is comprehensive if it has enough detail to ensure that cost elements are neither omitted nor double-counted, all cost-influencing assumptions are detailed in the estimate’s documentation, and a single work breakdown structure (WBS) is defined and all WBS elements are described in a WBS dictionary. While Bureau officials were able to provide us with several documents that included projections and assumptions that were used in the cost estimate, we found the estimate to be partially comprehensive because it is unclear if all life-cycle costs are included in the estimate or if the cost estimate completely defines the program. Additionally, we found the Bureau had four versions of WBSs with inconsistencies among them. For example, the Bureau’s standard WBS, operational plan WBS, decennial budget WBS, and the life-cycle cost estimate WBS contained differing numbers of major areas (e.g., program management and response data) and we could not determine how all the different areas fit together. Bureau officials stated that they have worked to create an agency-wide standard WBS and that the different versions of the WBS they provided to us were similar. Yet the Bureau did not provide evidence that demonstrated how the WBS related to each other. These issues reduce the reliability of the Bureau’s current life-cycle cost estimate, because as a result, we could not determine if all life-cycle costs are included in the cost estimate, and decision makers and others cannot know whether the total estimate fully accounts for all costs. However, the Bureau’s use of WBSs is an improvement over what we found in 2008 when the Bureau did not have a WBS in place at all. In addition, about $3 billion, or one-quarter, of the total cost of the census is represented by cost breakouts that are not in the Bureau’s WBS. These comprise dollar amounts for the annual 2020 Census enacted or requested budget line for fiscal years 2012 through 2017 and their out year estimates for 2021 through 2023. Bureau officials justified using such aggregate budget figures by describing much of these years’ costs as staff cost at headquarters and as relatively fixed in nature—basic requirements to conduct a decennial census.