We have consistently stressed the importance of IRS conducting tax compliance research. Likewise, analyzing compliance data can help IRS identify ways to enhance taxpayer compliance. Without such data, it is more difficult for IRS to decide whether its efforts to address specific areas of noncompliance should focus on non-enforcement activities, such as improved forms or publications, or enforcement activities. Analyzing the data can also help identify changes that could be made to tax laws and regulations that may improve compliance. In April 2016, IRS released its most recent tax gap estimate. IRS estimated that taxpayers should have paid an average of about $2.5 trillion dollars per year in federal taxes for tax years 2008 to 2010. IRS also estimated that taxpayers paid approximately $2.04 trillion voluntarily and on time for those years, on average, leaving $458 billion in unpaid taxes per year. However, IRS estimates that through late payments and enforcement actions it eventually will collect an additional $52 billion on average for those years, leaving the average net tax gap at $406 billion for 2008 to 2010, as shown in figure 1. The tax gap estimate is an aggregate estimate of the five types of taxes that IRS administers—individual income, corporation income, employment, estate, and excise taxes. For each tax type, IRS attempts to estimate the tax gap based on three types of noncompliance: (1) underreporting of tax liabilities on timely filed tax returns; (2) underpayment of taxes due from timely filed returns; and (3) nonfiling, when a taxpayer fails to file a required tax return altogether or on time. IRS has not developed specific estimates for the tax gap related to income earned from illegal activities (e.g., prostitution) or certain forms of fraud. However, if IRS discovers these types of income over the course of an audit, it could be included in the tax gap estimates. In general, refund fraud related to identity theft would not be included in the tax gap estimate because it does not involve evading a tax liability. The tax gap includes unintentional errors as well as intentional evasion, such as intentionally underreporting income, intentionally overreporting expenses, and engaging in abusive tax shelters or frivolous tax schemes. There is no single approach to estimating all of the components of the tax gap. IRS uses NRP examinations of a stratified, random sample of tax returns along with statistical modeling to produce estimates of noncompliance for the population of individual income tax return filers. Other areas of the tax gap are estimated using payment data or other statistical models. Each approach IRS uses is subject to non-sampling error and the areas of the estimate that are samples are subject to additional sampling errors. The uncertainty of the estimates is not readily captured by standard errors that typically accompany estimates based on sample data. For that reason, IRS does not report standard errors, confidence intervals, and statistical comparisons across years. Prior to the 2008–2010 estimate, IRS had released two other tax gap estimates that used data from NRP examinations: (1) a tax year 2001 tax gap estimate that was released in February 2007 and (2) a tax year 2006 tax gap estimate that was released in December 2011. As shown in figure 2, the gross tax gap estimate has increased, in nominal terms, from $345 billion for 2001 to $458 billion, on average, for 2008–2010, an increase of $113 billion or about 33 percent. However, when we adjusted for inflation (using fiscal year 2016 dollars), the gross tax gap estimates amount to $460 billion in 2001, $530 billion in 2006, and $509 billion in 2008–2010. The inflation-adjusted gross tax gap increased by about 11 percent from 2001 to 2008–2010; however, the 2008–2010 estimate is slightly lower, by about 4 percent, than the 2006 estimate. Over the three estimates, the voluntary compliance rate (VCR)—the percentage of owed tax for a given year that is paid voluntarily and timely—has decreased slightly from 83.1 percent for 2006 to 81.7, on average, for 2008–2010. IRS also estimated the VCR and distribution of tax liability for each component of the tax gap. Generally, employment taxes have the highest estimated compliance rates while individual income and estate taxes have the lowest estimated compliance rates. There was a decrease in the VCR for individual income tax from 79 percent for tax year 2001 to 74 percent in the recent 2008–2010 estimate. According to IRS, this decline, along with the individual income tax’s increase in the share of liability, contributes to the slight decline in the overall VCR. The amount of the tax gap that IRS estimated it would collect through enforcement efforts and late payments varied across the three estimates. In 2001, IRS estimated it would collect $55 billion and that figure would increase by $10 billion, to $65 billion in 2006. However, for the 2008– 2010 tax gap estimate, the enforced collections or late payments decreased by $13 billion per year, on average, from the 2006 estimate, to $52 billion. According to IRS, the methodology used to calculate prior estimates may have been too optimistic, resulting in an overstatement of as much as 25 percent. Additionally, IRS stated that the economic downturn in 2008 reduced the total tax liability from which IRS could collect revenue over this period. However, differences in the tax gap estimates across years may not all be attributed to changes in taxpayer behavior (voluntary compliance) or IRS enforcement activities. According to IRS, the tax gap estimates have increased in part because IRS included some new tax gap components and updated some methods, which it believes increased the comprehensiveness and accuracy of the estimates. IRS reported that changes in economic activity and changes in tax law and administration also contribute to differences in tax gap estimates over time. In our 2017 High-Risk Report we continued to include Enforcement of Tax Laws as a high-risk area. Key components of this high-risk area include both addressing the tax gap and improving tax compliance. IRS enforcement of the tax laws helps fund the U.S. government by collecting revenue from noncompliant taxpayers and, perhaps more importantly, promoting voluntary compliance by giving taxpayers confidence that others are paying their fair share. However, IRS still faces challenges to its capacity for implementing new initiatives and carrying out ongoing enforcement and taxpayer service programs under an uncertain budgetary environment. Given the estimated size of the tax gap, even modest reductions would yield significant financial benefits for the country. We have made numerous recommendations over time to help IRS, the Department of the Treasury (Treasury), and Congress address tax noncompliance. Nonetheless, as we have reported in the past, closing the entire gap is not feasible since it could entail more burdensome record keeping or reporting than the public is willing to accept or more resources than IRS is able to commit. For example, third-party information reporting has shown to improve accuracy of income reporting by individual taxpayers; however, it requires increased record keeping and reporting by the third party and requires IRS resources to properly match the third-party information to individual tax returns. Underreporting of tax liabilities accounted for most of the tax gap estimate for tax years 2008–2010, making up 84 percent of the entire estimated gross tax gap, as shown in figure 3. Individual income taxes made up the largest portion of underreporting, followed by employment taxes and corporation income taxes. Underreporting of business income accounted for nearly half of the individual income tax underreporting gap. This includes income from sole proprietors, which accounted for the largest share of individual income tax underreporting, as shown in table 1. Most business related income tax return items also had high net misreporting percentages, which is the sum of the net misreported amount divided by the sum of the absolute values of the amounts that should have been reported, as a percentage. To show additional detail on aspects of the tax gap, we conducted some additional analysis on selected line items of the individual NRP data, which is presented in appendix II. As we have previously reported, the extent to which individual income tax taxpayers accurately report their income is closely aligned to the amount of income that is reported to them and to IRS by third parties. For example, according to 2008–2010 IRS data, taxpayers misreported over half of the types of income for which there is little or no third-party information reporting, such as business income. In contrast, when employers withhold taxes and report the wages and salaries to employees and IRS through Form W-2, Wage and Tax Statement (W-2), there is better compliance. As shown in figure 4, 1 percent of these types of income were misreported while nearly 99 percent were accurately reported on individual income tax returns. Similarly, taxpayers misreported less than 10 percent of income for which banks and other financial institutions provided information returns (Forms 1099) to account holders and IRS that show taxpayers’ annual income from some types of investments. Generally, new requirements on third parties to submit information returns would require statutory changes. We have previously identified additional information reporting opportunities as well as improvements that IRS could make on its own to existing forms and how it uses them. For example, we suggested in August 2008 that Congress may wish to make all taxpayers with rental real estate activity subject to the same information reporting requirements as other taxpayers operating a trade or business; however, no legislative action has been taken on this suggestion. We recommended in August 2010 that IRS require mortgage-secured property addresses to be reported on other forms (Forms 982 and 1099-C) to help IRS detect taxpayers who fail to pay taxes on certain forgiven mortgage debts. Legislative and executive actions have been taken consistent with our recommendation. However, IRS has not revised two forms to collect specific information from taxpayers and lenders concerning the amount of forgiven debt attributable to a principle residence and the locations of a taxpayer’s principle residence. For items subject to substantial third-party information reporting, IRS is able to use automated processes to address noncompliance. The automated underreporter program, through which IRS matches amounts reported on returns with amounts reported on information returns submitted by third parties, is one such process. This computer matching program allows IRS to identify discrepancies between tax returns and information returns and propose automatic changes to taxpayers. For items with little to no third-party information reporting, IRS has to rely on more resource-intensive methods, such as correspondence or face-to- face examinations, to address noncompliance. While these examinations may be started by reviewing specific line items, they may also be expanded to cover other areas of the tax returns if there are indications of misreporting in areas of the return not previously identified. However, it is harder for IRS to detect noncompliance in areas with little third-party information reporting. The second largest part of the underreporting tax gap is made up of employment taxes, which are comprised of three main components: self- employment tax, Federal Insurance Contribution Act (FICA) Social Security and Medicare withholding, and Federal Unemployment Tax Act (FUTA) taxes, as shown in table 2. The self-employment component is estimated from IRS’s NRP individual income tax data. However, IRS lacks NRP data for other components of employment tax. Therefore, it estimates both FICA and FUTA by applying the estimated compliance rates from a 1993 employment tax gap report, which used tax year 1984 employment tax return data, to the current reported taxes. IRS recently completed an NRP study of employment tax returns that reviewed federal income tax withholding and FICA, the first such study IRS had conducted in over 30 years. We reported that although the examinations for the study were completed, IRS had not developed formal plans to analyze the results to (1) identify areas of noncompliance, (2) address such noncompliance, or (3) update its employment tax gap estimate. According to IRS officials, they had not developed formal plans due to competing research priorities and limited resources and because the NRP results had not yet been finalized. We recommended that IRS develop plans to analyze the NRP results in 2017 to address areas of noncompliance identified and update its employment tax gap estimates. IRS agreed with our recommendations and stated that it will be determining how to use the data from this new study to update the employment tax gap estimate. As shown in table 3, IRS developed corporation income tax underreporting estimates for two types of corporations: small corporations (those without a balance sheet or with assets less than $10 million) and large corporations (those with assets of $10 million or more). IRS estimated the voluntary compliance rate for all corporations to be 83 percent for tax years 2008–2010. The estimates are based on adjusted data from operational examinations, which focus on the tax returns most likely to have substantive noncompliance rather than examinations of a statistically representative sample of corporation tax returns. IRS does not have a program comparable to NRP for corporation income tax because of the difficulty of constructing a representative sample for a small group of highly diverse large corporations, among other reasons. The limited scope and selection criteria for non-NRP examinations introduce statistical bias, meaning that the examination issues and results from examinations of corporation tax returns are not necessarily representative of the overall corporation population. However, IRS has developed some methods to project the results of the examinations to the larger population of corporations, and, despite these limitations, IRS considers the corporation estimates to provide a rough gauge of corporation income tax noncompliance. IRS’s divisions responsible for large and small corporation examinations each have management systems in place to track issues identified from corporation examinations. While this information is not derived from the tax gap estimates, IRS has identified several common examination issues for both large and small corporations, as shown in table 4. For the 2008–2010 tax gap estimate, IRS for the first time estimated the net tax gap by each type of tax, as shown in table 5. Unlike most of the tax gap, IRS can tabulate late payments. Since enforcement and other late payments often happen many years after a given tax year has ended, IRS must project into the future to estimate how much tax it will eventually collect for that tax year. IRS expects to recoup the smallest percentage of taxes from the gross individual income tax estimate. IRS officials stated IRS believes the tax gap estimates are sufficiently reliable for the intended purpose of providing a snapshot of tax compliance as a whole. The tax gap estimate is actually many estimates used together to develop one overall picture of tax compliance. IRS has more certainty in some areas of the estimate than others. Generally, IRS officials consider those components of the tax gap estimate that are based on the most current data (2008–2010 data) to be more robust. However, as shown in table 6, IRS recognizes that some component estimates of the tax gap estimate are more uncertain than others, in part because some component estimates rely on older data and it is inherently difficult to estimate some types of noncompliance. IRS has no estimates for some areas of the tax gap. According to IRS officials, IRS has higher amounts of confidence in all of the underpayment components, because they are based on data from systems that can distinguish enforcement and late payments from other payments (IRS has the most confidence in these components); the individual income nonfiling component, because it is based on a new methodology combining two methods that incorporate improvements to the methods used in prior estimates; the individual income underreporting component, because it is primarily based on adjusted NPR examination data, which is a statistically representative sample of individual tax returns; and the corporation underreporting component, because it is based on operational examination data, adjusted for selection bias. IRS has a lesser amount of confidence in the estate nonfiling and underreporting data, because they are forecasts updating estimates based on assumptions made in studies completed in 2000; and the withholding taxes (FICA and FUCA) part of the employment underreporting data, because the data are partially a forecast based on data from an older compliance study. The methodologies used to develop the component estimates differ by component, resulting in a mix of statistical sample and operational-based data being used, as well as forecasts from earlier estimates. IRS is therefore unable to calculate confidence intervals for any of the tax gap estimates. IRS officials stated that that they continue to try to identify a value for those components without estimates, such as corporation income, excise tax nonfiling, and excise tax underreporting, but have not yet found a sufficiently reliable data source nor method upon which to base estimates. To increase its confidence in the estimates of underreported individual income, IRS uses an econometric technique called detection controlled estimation (DCE). This regression-based model controls for variables that could affect the amount of underreporting IRS examiners detected. IRS uses this adjustment because it knows its examiners do not detect all underreported income during examinations, and therefore it adjusts the NRP data to account for such undetected income when estimating the tax gap. The statistical technique estimates the noncompliance detected by a hypothetical “best practices” examiner—an ideal that is unattainable—and then statistically estimates the noncompliance detected by the hypothetical examiner to adjust upward the findings from research examinations conducted by actual examiners. The DCE adjustment accounts for more than half (about $150 billion) of the total individual income tax underreporting estimate. IRS also used the DCE adjustment for the self-employment tax estimates used in the employment tax underreporting estimate. Appendix III provides more information on the extent to which DCE adjustments contributed to the 2008–2010 tax gap estimate. IRS has taken steps to improve the tax gap estimate. For example, IRS used an updated methodology to calculate the estimated nonfiling amount for the 2008–2010 estimate that combined two prior methodologies. Specifically, IRS expanded how it matches information between the U.S. Census Bureau’s annual Current Population Survey and IRS data to estimate the amount of taxes that were not filed. IRS believes this updated methodology allows it to create a better matched dataset and identify nonfilers more accurately. See appendix IV for details on changes to IRS’s tax gap methodology. IRS plans to release its next tax gap estimate in 2019 to cover tax years 2011 to 2013. IRS is also undertaking several additional studies that may offer data IRS can use to improve the tax gap estimate, including these examples: Taxpayers’ tipping behavior: IRS is surveying taxpayers to help estimate total tip income and tipping rates by industry/occupation and by major method of payment (e.g., credit card, debit card, and cash). Limited studies on C corporations and other midsize corporations: IRS studied compliance of C corporations with assets less than $250,000 and with a balance sheet, and corporations with assets of $10 to $50 million for tax year 2010. These studies plan to identify potential areas of noncompliance. Partnership misreporting pilot: In 2016, IRS initiated this study to measure reporting compliance for certain partnerships, as well as to estimate tax misreported at the taxable partner level as a result of partnership misreporting. This study was initiated in response to a recommendation from a prior report. NRP employment tax estimates: As previously mentioned, IRS is determining how it will use the NRP employment tax study it concluded in 2017 to improve the tax gap estimates. IRS’s current strategic plan (2014–2017) discusses general approaches to make voluntary compliance easier for taxpayers and to ensure taxes owed are paid. However, in some areas, the plan does not include specific tactics for improving compliance strategies. Rather, it addresses the elements of voluntary compliance and enforcement actions through two of its goals: Delivering high-quality and timely service to reduce taxpayer burden and encourage voluntary compliance. Effectively enforcing the law to ensure compliance with tax responsibilities and combat fraud. IRS officials stated the strategic plan goals are a component of IRS’s Future State—which is a vision for agency-wide operations that aims to improve services across different taxpayer interactions such as individual account assistance, exams, and collections—and are directly reflected in three of its six themes: facilitate voluntary compliance by empowering taxpayers with secure innovative services, tools, and support; understand noncompliant taxpayer behavior, and develop approaches to deter and change it; and select highest value work using data analytics and a robust feedback loop. According to IRS officials, the remaining themes support these goals indirectly by seeking to improve IRS’s effectiveness. IRS officials noted the IRS Future State vision has outlined two measures that will support the overall goal of increased compliance. The first will be the percentage of compliance issues resolved within 1 year of filing. The second is the percentage of taxpayers with recurring compliance issues. However, IRS has not yet determined the target levels for these goals. According to officials, the levels for these goals will be published with the next IRS strategic plan (2018–2022), which IRS is scheduled to release in mid- 2018. IRS previously set or acknowledged quantitative goals to improve voluntary compliance. However, IRS has since moved away from that approach. In 2005, we recommended that IRS establish a long-term quantitative voluntary compliance goal for individual income tax underreporting and for tax underpayment, as well as for other areas of noncompliance. IRS agreed with the concept of our recommendation and, in response, established a voluntary compliance rate goal of 85 percent by 2009, which was published in IRS’s fiscal year 2007 budget request. In 2006, Treasury issued its Comprehensive Strategy for Reducing the Tax Gap, with a seven-component strategy for reducing the tax gap: (1) reduce opportunities for evasion, (2) make a multiyear commitment to research, (3) continue improvements in information technology, (4) improve compliance activities, (5) enhance taxpayer service, (6) reform and simplify the tax law, and (7) coordinate with partners and stakeholders. In 2007, IRS developed a more detailed report that emphasized the same seven components outlined in the Treasury report and also outlined projects, initiatives, legislative proposals, and other actions designed to combat the sources of noncompliance. In the 2007 report, IRS acknowledged the goal set by the then Chairman of the Senate Finance Committee for IRS to meet a 90 percent voluntary compliance rate by tax year 2017 and the goal set by the IRS Oversight Board of 86 percent by tax year 2009. In 2009, IRS published another report that followed up on the efforts discussed in the 2006 and 2007 Treasury and IRS reports. However, IRS has not published any reports since that time that focus on goals for reducing the tax gap. In 2012, Treasury, along with IRS, set an agency priority goal to increase voluntary tax compliance from 83.1 to 86 percent by September 30, 2013. However, Treasury and IRS decided not to renew the agency priority goal because they said the measure did not satisfy the criteria of having indicators and quarterly milestones against which to track process or being able to determine whether the goal has been achieved by the end of a 2-year period, as established by the Office of Management and Budget. Since the tax gap estimates are only updated every few years, Treasury and IRS officials said there was no way for Treasury or IRS to show improvements or declines in meeting the goal on a quarterly basis or over the 2-year goal term. More recently, IRS officials told us that while they want to achieve a high level of voluntary compliance, neither IRS nor Treasury has set a recent high level department- or agency-wide quantitative goal aimed at reducing the tax gap or increasing voluntary compliance. Establishing clear compliance goals and measuring progress toward them benefit both IRS and external stakeholders and are consistent with the results-oriented performance management principles set forth in the Government Performance and Results Act of 1993 and the GPRA Modernization Act of 2010. As we have previously reported, setting long-term strategic goals is essential for results-oriented management, because such goals explain in greater specificity the results an agency is intending to achieve. The goals form a basis for an organization to identify potential strategies for fulfilling its mission and for improving its operations to support achievement of that mission. Directly aligning strategic goals and strategies for achieving those goals is important for assessing an agency’s ability to achieve those goals. Further, when program results could be influenced by external factors, agencies can use intermediate goals and measure to identify the program’s discrete contribution to a specific result. IRS has moved away from specific numeric goals to improve compliance because it now believes there are limited benefits to them. According to IRS officials, IRS actions alone do not determine the level of taxpayer compliance and there are also several challenges associated with establishing meaningful and useful compliance goals. IRS officials reported that many of these challenges are due to the tax gap only being estimated every few years. As a result, fluctuations in the estimate over time may not be generally attributed to changes in compliance behavior but the fluctuations might instead result from the imprecision of the estimates or updated methodologies. According to IRS, changes in the economy may also have an effect on tax compliance rates. For example, a downturn in the economy would likely result in less tax needing to be paid, but it might also cause some taxpayers to comply less than they otherwise would. Further, separating those two effects would be difficult, particularly given the unobserved nature of most noncompliance. Finally, IRS officials stated other factors, such as IRS services, enforcement efforts, evolving social norms, or changes in legislation, may affect the overall compliance rate. Although IRS may not have full control over all of the factors that affect voluntary compliance, it does have an impact on taxpayer’s compliance through its service and enforcement programs. Furthermore, IRS is not alone in not having full control over the results it seeks to achieve. A number of methods can be used to map or model the causal relationships among the inputs, processes, and outputs produced by various strategies and the forces that influence achievement of outcomes, such as results mapping and logic modeling. Recognizing that outside influences may present risks or challenges to achieving outcomes, OMB Circular Number A-11 states that while agencies cannot mitigate all risks related to achieving strategic objectives and performance goals, they should identify, measure, and assess challenges related to mission delivery, to the extent possible. We have previously reported that setting long-term quantitative goals for IRS offers several benefits. First, compliance goals coupled with periodic measurements of compliance levels would provide IRS with a better basis for determining to what extent its various service and enforcement efforts contribute to compliance. Second, long-term, quantitative goals would help IRS consider new strategies to improve compliance, especially since these strategies could take several years to implement. Third, focusing on intended results can promote strategic and disciplined management decisions that are more likely to be effective because managers who use fact-based performance analysis are better able to target areas most in need of improvement and to select appropriate interventions. Fourth, agency accountability can be enhanced when both agency management and external stakeholders—such as Congress—can assess an agency’s progress toward meeting its goals. Likewise, a survey of the Organization for Economic Cooperation and Development countries and other advanced economies found that some governments are paying increased attention to estimating tax gaps for their major types of taxes. Several countries shared their quantitative goals for reducing the tax gap or increasing their tax revenue with the survey. For example, Denmark set a target to ensure that the tax gap does not exceed 2 percent of estimated total tax liability. Without long-term, quantitative voluntary compliance goals and related performance measures, it will be more difficult for IRS to determine the success of its strategies, adjust its approach when necessary, and remain focused on results, especially since factors that affect compliance change over time. Having compliance goals as IRS has had in the past, coupled with data, would provide a solid base upon which IRS could develop a more strategic, results-oriented approach to improving compliance. IRS officials told us tax gap data are used as a high-level overview of tax compliance. IRS officials also stated they use the underlying tax gap data (i.e., NRP data and other data) in several ways to update compliance efforts. However, IRS has not documented a comprehensive strategy that shows, for example, how it intends to analyze and use the tax gap data, particularly from the NRP, to develop or improve compliance programs. IRS officials told us they use the NRP data to study specific compliance behaviors. For example, IRS has studied taxpayer behavior in claiming the Earned Income Tax Credit (EITC), the child tax credit, and the additional child tax credit. Sometimes these studies are used to develop legislative proposals that are included as part of the annual budget process and outlined in Treasury’s annual revenue proposals. Officials stated the legislative proposals are based on the knowledge of compliance derived from analysis of NRP data and they are organized into themes, such as reducing the tax gap, improving voluntary compliance, or improving tax administration. However, these revenue proposals are requests for changes to the tax laws and, ultimately, it is at Congress’s discretion whether to enact them. IRS officials reported that other times NRP data are used to compute the annual improper payment rate for the EITC. According to officials, IRS also uses these data to annually categorize the root causes of EITC noncompliance. IRS uses the NRP data to update compliance plans by updating the Discriminate Function (DIF) formulas. DIF formulas are designed to score returns for the likelihood that the tax reported on the return is significantly underreported. DIF scores help IRS ensure that noncompliant taxpayers are more likely to be selected for examination and compliant taxpayers are less likely to be unnecessarily examined. IRS determines DIF scores for individual income, small corporation income, partnership, and S corporation returns. IRS officials described high-level concepts of how the various NRP and other studies contribute to compliance and enforcement strategies. Officials from IRS’s Office of Research, Applied Analytics, and Statistics (RAAS) said they think the various uses of the NRP are widely known from general documentation about the NRP and its study design. RAAS officials also noted the fiscal year 2009 budget justification that led to special funding for the NRP still reflects IRS’s current strategy for undertaking various NRP studies. Further, IRS officials pointed us to documentation from the 2000s that discussed a need for a multiyear research commitment and IRS’s goal to move NRP studies beyond the individual income tax to include other taxes. We previously recognized IRS’s commitment to multiyear research and have noted the gains it has made in regularly estimating compliance. Our analysis of the decade-old documents found evidence of a commitment to research that generally seemed sufficient for that period. However, IRS officials did not provide us more recent documents that describe its current efforts to study compliance or show how it plans to use NRP data to update compliance strategies. IRS officials also provided us with business plans for some of their other business units and divisions. The plans we reviewed noted, at a high level, that data and analysis will be used to improve workload selection but did not discuss how specific research efforts or the results of those efforts would be integrated into the missions. The Internal Revenue Manual section on the NRP states that IRS needs to measure taxpayer compliance with federal income tax laws along with contributing factors so that customer-focused programs and services can be enhanced or developed and so that compliance information and tools can be improved. A 2001 NRP prospectus states the NRP will help to increase public confidence in the fairness of our tax system by helping IRS identify where compliance problems occur and focus its resources accordingly. Further, it states that for strategic planning and budget purposes, IRS requires regular estimates of compliance. The NRP research efforts support this critical need. According to IRS, the NRP will also improve IRS’s ability to detect noncompliance; reduce the burden of unnecessary IRS contacts on compliant taxpayers; and support the strategic goals, program development, and resource allocation of IRS operating divisions. Using quality information, such as NRP data, to achieve the agency’s objectives is one of the 17 principles for internal controls. Further, the standards for internal controls also recognize documentation is a necessary part of an effective system, but the level and nature of documentation vary based on the size of an entity and the complexity of the operational process. Documentation is required to demonstrate the design, implementation, and operating effectiveness of a system. Considering the size and relative importance of the tax gap, documenting a strategy for how IRS plans to use NRP data to reduce the tax gap would be consistent with internal controls. However, without a strategy that provides an overall picture of how NRP data are used, it may be difficult for Congress and other decision makers to understand the merits of what they are being asked to fund. Further, without developing and documenting a strategy for incorporating the results of NRP data, IRS risks not fully leveraging the compliance data it collects or not allocating enforcement resources in the most cost-effective manner. We have a long-standing history of reporting on the need for IRS to develop a comprehensive compliance strategy: In 1994, we concluded that until IRS produces a comprehensive compliance strategy, existing data could be used as part of an interim compliance strategy that directs resources at the most noncompliant taxpayers. We found that using such a starting point, IRS could focus more of its efforts on highly noncompliant areas, such as small corporation income and sole proprietorship income that made up almost a third of the tax gap. In 2005, we concluded that reducing the tax gap will be a challenging task given persistent levels of noncompliance and will not likely be achieved through a single solution. Rather, the tax gap must be attacked on multiple fronts and with multiple strategies over a sustained period, thus building a foundation to help taxpayers voluntarily comply. Between 2005 and 2007, we testified six times on the need for IRS to develop a strategy to attack the tax gap on multiple fronts with multiple approaches. In 2007, we reported on the need for IRS to develop a strategy to address noncompliant sole proprietor income, which accounts for a significant share of the tax gap. Further, documenting a strategy for using NRP data to guide compliance efforts would be consistent with two key criteria for removal from the High-Risk List: Action plan: A corrective action plan exists that defines the root cause and solutions and that provides for substantially completing corrective measures, including steps necessary to implement solutions we recommended. Demonstrated progress: Ability to demonstrate progress in implementing corrective measures and resolving the high-risk area. The nation’s long-term fiscal projections show that the federal government is on an unsustainable fiscal path. One way to help improve the nation’s fiscal position would be to reduce the tax gap. Reducing the tax gap will be a challenging task given persistent levels of taxpayer noncompliance. However, even modest reductions would yield significant financial benefits and help improve the government’s fiscal position. IRS has shown a continued commitment to study sources of noncompliance and has made strides in improving NRP and other tax gap data. However, additional efforts could further assist IRS in addressing the tax gap. A long-term, quantitative goal for improving voluntary compliance may provide IRS with a concrete target the agency can use in fulfilling its mission. Without a quantitative goal, it will be more difficult for IRS to determine the success of its strategies, adjust its approach when necessary, and remain focused on results, especially since factors that affect compliance change over time. Likewise, a strategy that outlines how IRS plans to use NRP data to update compliance strategies would help IRS determine resource tradeoffs and more fully leverage the investment it makes in compliance research, while providing Congress with a better understanding of the merits of the research it is being asked to fund. We are making the following two recommendations to IRS: The Commissioner of Internal Revenue should re-establish long-term, quantitative goals for improving voluntary compliance. (Recommendation 1) The Commissioner of Internal Revenue should instruct the appropriate officials to develop and document a strategy that outlines how IRS will use National Research Program data to update compliance strategies that could help address the tax gap. (Recommendation 2) We provided a draft of this report to the Commissioner of Internal Revenue. IRS provided written comments, which are summarized below and reprinted in appendix V. IRS also provided technical comments, which we incorporated where appropriate. IRS disagreed with our recommendation that it re-establish long-term, quantitative goals for improving voluntary compliance. In its letter, IRS stated that the voluntary compliance rate is ill-suited as a strategic or performance metric for IRS for various reasons. For example, IRS stated that improving voluntary compliance, determining the success of its strategies, and adjusting its approach could be accomplished in the absence of a quantitative goal. However, as we note in the report, setting long-term strategic goals is essential for results-oriented management, because such goals explain in greater specificity the results an agency is intending to achieve. Further, focusing on intended results can promote strategic and disciplined management decisions that are more likely to be effective because managers who use fact-based performance analysis are better able to target areas most in need of improvement and to select appropriate interventions. IRS also stated that its actions alone do not determine the level of voluntary compliance, which is determined by the interaction of many factors, such as taxpayer behavior, tax law complexity, and IRS resources. We agree that IRS may not control all factors that affect voluntary compliance. However, IRS does influence taxpayer compliance through its service and enforcement programs. Furthermore, as we point out in the report, while agencies cannot mitigate all outside influences that may present risks or challenges to achieving outcomes, they should identify, measure, and assess such challenges to the extent possible. Given the benefits of setting long-term quantitative goals—as discussed in this report—we continue to believe it is prudent for IRS to establish such goals. IRS agreed with our recommendation that it develop and document a strategy that outlines how IRS will use National Research Program data to update compliance strategies that could help address the tax gap. As agreed with your office, unless you publicly announce the contents of this report earlier, we plan no further distribution until 30 days from the report date. At that time, we will send copies to the Chairmen and Ranking Members of other Senate and House committees and subcommittees that have appropriation, authorization, and oversight responsibilities for IRS. We will also send copies of the report to the Commissioner of Internal Revenue and other interested parties. In addition, this report will be available at no charge on the GAO website at http://www.gao.gov. If you or your staff has any questions about this report, please contact me at (202) 512-9110 or mctiguej@gao.gov. Contact points for our offices of Congressional Relations and Public Affairs are on the last page of this report. GAO staff members who made major contributions to this report are listed in appendix VI. Our objectives were to determine (1) the main drivers of the tax gap; (2) the Internal Revenue Service’s (IRS) confidence in the tax gap estimates; (3) IRS goals, if any, for reducing the tax gap; and (4) the extent to which IRS uses tax gap estimates and underlying data to develop strategies and actions to reduce the tax gap. To determine the main drivers of the tax gap and IRS’s confidence in the estimates, we reviewed IRS’s tax gap estimates and underlying data; IRS technical papers and reports; third-party reviews of the data; and past GAO and Treasury Inspector General for Tax Administration reports on the 2001, 2006, and 2008–2010 tax gap estimates. We also interviewed officials from IRS’s Office of Research, Applied Analytics, and Statistics (RAAS) who are responsible for estimating the tax gap. We determined that IRS’s tax gap and compliance estimates were sufficiently reliable for the purposes of this report, particularly since IRS already has publicly released its tax gap estimates and disclosed their limitations. These purposes include discussing the major tax gap components, the orders of magnitude for various components, and IRS’s opinions about the certainty of its estimates. To determine IRS’s goals for increasing voluntary compliance, we reviewed IRS’s and the Department of the Treasury’s (Treasury) strategic plans and Treasury’s General Explanations of the Administrations Fiscal Year Revenue Proposals (commonly referred to as the Green Book) from 2011 to 2017. We also reviewed other IRS and Treasury documentation, such as the strategies for improving voluntary compliance that were developed in the mid-2000s. Additionally, we reviewed Treasury’s agency priority goals, including the goal it set in 2012 to increase voluntary compliance. We also reviewed the statutory requirements for agency performance goals under GPRAMA. We interviewed Treasury officials in the Office of Tax Analysis and the Office of Strategic Planning and Performance Improvement about prior goals that were set and the goal- setting process. We interviewed IRS officials responsible for developing strategies and establishing goals to reduce the tax gap, specifically officials in the Deputy Commissioner’s Office for Service and Enforcement and the Small Business/Self-Employed, Large Business and International, and Wage and Investment divisions. To determine the extent to which IRS uses the tax gap and other underlying data to update compliance efforts, we requested documentation on any plans or strategies that show how the various tax gap and other compliance studies work together toward a larger compliance strategy. We found that the agency had not developed these documents. We interviewed staff from the Deputy Commissioner’s Office for Service and Enforcement and RAAS about the agency’s plans to use tax gap data and other compliance studies when developing compliance strategies. To show additional detail on aspects of compliance using the same data upon which the individual income tax underreporting tax gap estimates are based, we examined IRS’s tax gap estimates for tax years 2008– 2010 and the underlying data from its National Research Program (NRP) study of individual income tax returns. This information is presented in appendix II. Unlike other IRS examinations, NRP examinations can be used to estimate taxpayer reporting compliance because they are drawn from a stratified, statistically representative sample of the population of individual income tax returns. We interviewed IRS officials from RAAS about their research and analysis of the NRP data, and we gathered related documentation where available. IRS officials described the quality review and data reliability processes they used to collect data from the NRP examinations. Because the NRP sample was based on random selections, the sample was only one of a large number of samples that IRS could have drawn. Since each sample could have provided different estimates, we express our confidence in the precision of our estimates based on the sample as a 95 percent confidence interval plus or minus a margin of error. This is the interval that would contain the actual population value for 95 percent of the samples that could have been drawn. The estimates presented in appendix II have margins of error of less than 10 percent or 10 percentage points. In analyzing the NRP data, we conducted several reliability tests to ensure the data we used were sufficiently complete. For example, we electronically tested the data for obvious errors. We concluded that the data were sufficiently reliable for the purposes of this report based on these steps and on our previous reviews of tax gap estimates and NRP data. We conducted this performance audit from July 2016 to October 2017 in accordance with generally accepted government auditing standards. Those standards require that we plan and perform the audit to obtain sufficient, appropriate evidence to provide a reasonable basis for our findings and conclusions based on our audit objectives. We believe that the evidence obtained provides a reasonable basis for our findings and conclusions based on our audit objectives. We analyzed the raw National Research Program (NRP) data for individual income tax returns, including itemized deductions, for tax years 2008–2010. These data do not account for the undetected income that the Internal Revenue Service (IRS) adjusts for when developing tax gap estimates. Therefore these data are not comparable to the tax gap data presented elsewhere in this report, but they allow additional analysis of areas of misreporting. Table 7 provides greater details on certain line items from the individual income tax return that align with various third-party information reporting levels determined by IRS. Line items with substantial or some information reporting tended to have lower overall misreporting percentages. Line items that had the largest percentage of taxpayers with misreported income were those for sole proprietor and farming income, both of which are subject to little to no information reporting. Based on the analysis of these data, we also estimate that line items with the largest mean amounts of underreporting are business sale and supplemental income or loss; the business sale line item also has the largest mean amount of overreporting, averaging $21,000 per return; and sole proprietor income and farm income have very similar misreporting data; over 75 percent of the income is misreported and, of that, over 80 percent is under reported while under 20 percent is overreported. We also analyzed selected credits and deductions to determine the average noncompliance rates of these line items, as shown in table 8. Because credits and deductions offset taxpayers’ income or tax owed, taxpayers who underreported a credit or deduction overreport their tax liability or tax owed; taxpayers who overreport a credit or deduction underreport their tax liability or tax owed. However, we did not determine the extent to which misreporting was because of issues specific to how taxpayers claimed the credits and deductions or because taxpayers misreported their income, which could affect eligibility for certain credits and deductions. For example, the 2016 income limit to claim the Earned Income Tax Credit (EITC) is $39,296 for single, surviving spouse, or head of household taxpayers with one qualifying child. If IRS determined that such taxpayers who claimed the EITC and reported less than $39,296 in income on their tax returns had underreported their income in order to stay under the threshold, those taxpayers would no longer be eligible for the credit and would have overreported the credit. Based on the analysis of these data, we estimate that of the selected credits, EITC is the most claimed credit and about half of the time it is misreported; thirty-five percent of the time the child tax credit was misreported with about two- thirds of that being underreported, which is inconsistent with filing patterns for most of the other credits and deductions; of the selected deductions, the deduction for real estate taxes is most often claimed and about a quarter of the time it is misreported; the medical expenses line item has the highest percentage of misreporting; 80 percent of the time the deduction is overreported; and the mortgage interest deduction has the highest average overreported amount, over $4,000 per return. In estimating the individual income tax gap, the Internal Revenue Service (IRS) applies an econometric technique called detection controlled estimation (DCE), which is a regression-based model that controls for variables that could affect the amount of underreporting detected. The statistical technique first produces a hypothetical ‘‘best practices’’ examiner—an ideal which is unattainable—based on who conducted the examinations and the observed examination results. It then statistically estimates the noncompliance detected by the hypothetical examiner to adjust upward the findings from research examinations conducted by actual examiners. The technique estimates total undetected underreporting by imputing the average underreporting undetected by IRS’s National Research Program (NRP) examination to the detected underreporting, controlling for certain return line item characteristics. According to IRS officials, this approach is reasonable and the best currently available to attempt to estimate the full amount of underreported individual income. As shown in table 9, more than half of the underreporting component of the tax gap consists of income that IRS did not detect during examinations. DCE is not applicable to the underpayment and nonfiling components of the tax gap. In efforts to improve the tax gap estimates, the Internal Revenue Service (IRS) updated two areas of the 2008–2010 tax gap estimate by developing updated methodologies. Nonfiling individual income tax: IRS summed together the total of taxpayers who do not file tax returns and those who filed late. The 2008–2010 estimate of taxpayers not filing a return was made by combining the two methods used to estimate the 2006 and 2001 tax gap estimates. In 2006, IRS used a sample of individuals not appearing on filed tax returns. In 2001, IRS conducted an “exact match” between the Census Bureau’s annual Current Population Survey and IRS data. The 2008–2010 estimate of late filers was based on the total balance due from late filed tax returns, adjusted for income reported to IRS on information returns. IRS believes its current methodology is an improvement over the 2006 estimate as it uses the population data rather than a sample, avoiding disadvantages resulting from sampling. IRS reported improvements in the Census and IRS information associated with nonfilers allowed them to create a better matched dataset and identify nonfilers more accurately. Nonfiling self-employment data: The methodology IRS used to calculate self-employment tax nonfiling is the same that it used for individual income tax. However, for the 2008–2010 estimate, IRS changed where it reports self-employment tax nonfiling within the tax gap estimate. For the 2008–2010 estimate, this tax is now reported in the employment tax category, whereas for the 2001 and 2006 estimates it was reported in the individual income tax category. IRS officials stated that for the 2006-2010 estimate IRS decided to break self-employment out separately and report it with the employment tax because they believe it allows a more comprehensive view of employment taxes. IRS also updated how the underlying data supporting the tax gap are organized in two ways: Changes in net tax gap estimates: As previously mentioned, IRS published net tax gap estimates by each tax type (individual income, corporation income, employment, and estate tax) for the first time in the 2008–2010 estimate. IRS officials stated that they made progress by providing this data. However, IRS is unable to break out the net tax gap further by tax component because during examinations, adjustments are not categorized by component (i.e., underreporting, underpayment, and nonfiling). Changes in individual income underreporting: Starting in 2008– 2010, IRS modified the categories it uses to break down the individual income underreporting component. These changes affect how IRS calculates the net misreporting percentage (NMP) for individual income tax, but not how it calculates the tax gap. IRS uses the NMP to show the relationship between third-party information reporting and individual income tax reporting compliance. IRS reported the changes reflect an improvement in methodology. IRS cautions that any comparison of the 2008–2010 NMP to the 2006 NMP estimates should consider those improvements. The prior calculation method involved adding offsets to income, such as deductions, exemptions, and adjustments, which distorted the comparison across categories. IRS determined a better approach was to combine income items into categories and to report offsets to income as a separate category. (See figure 5.) In addition to the contact named above, Jeff Arkin (Assistant Director), James Ashley, Jehan Chase, Charles Fox, John Hussey, Donna Miller, John Mingus, Edward Nannenhorn, Cynthia Saunders, Robyn Trotter, and Elwood White made significant contributions to this report.

Summary: The tax gap—the difference between tax amounts that taxpayers should have paid and what they actually paid—has been a persistent problem for decades. The tax gap estimate is an aggregate estimate of the five types of taxes that IRS administers—individual income, corporation income, employment, estate, and excise taxes. For each tax type, IRS attempts to estimate the tax gap based on three types of noncompliance: (1) underreporting of tax liabilities on timely filed tax returns; (2) underpayment of taxes due from timely filed returns; and (3) nonfiling, when a taxpayer fails to file a required tax return altogether or on time. GAO was asked to review IRS's tax gap estimate for tax years 2008 to 2010. This report provides information on (1) the main drivers of the tax gap; (2) IRS's confidence in the tax gap estimates; (3) IRS's goals, if any, for reducing the tax gap; and (4) the extent to which IRS uses tax gap estimates and underlying data to develop strategies to reduce the tax gap. GAO reviewed IRS tax gap data and reports and interviewed IRS officials. The Internal Revenue Service's (IRS) latest tax gap estimate found that taxpayers voluntarily and timely paid about 81.7 percent of the taxes they should have paid for tax years 2008-2010. As with past estimates, underreporting of individual income taxes accounted for the largest portion of the 2008-2010 tax gap. IRS believes the tax gap estimates are sufficiently reliable to provide a snapshot of tax compliance as a whole because much of the estimates are based on the most current data available, such as from IRS's National Research Program (NRP). IRS previously set or acknowledged goals to improve voluntary compliance. However, IRS has since moved away from that approach. IRS officials now believe there are limited benefits to establishing goals because IRS cannot control all aspects of compliance and updated methodologies may cause fluctuations in the estimates. IRS does, however, have an impact on taxpayers' compliance through its service and enforcement programs. Without long-term, quantitative goals for improving voluntary compliance, it will be difficult for IRS to determine the success of its compliance efforts and adjust its approaches. The Internal Revenue Manual states IRS needs to measure taxpayer compliance and other factors so compliance information and tools can be improved. IRS uses tax gap data to study compliance behaviors and update computer formulas designed to identify tax returns with a high likelihood of noncompliance. Yet IRS has not documented a comprehensive strategy that shows how it intends to use NRP data to update compliance strategies. Officials said the uses of NRP are widely known from general documentation about NRP. Without developing and documenting a strategy for using the NRP data to update compliance strategies, IRS may not fully leverage the compliance data or allocate enforcement resources in the most cost-effective manner, and it may be difficult for Congress and others to understand the merits of what they are being asked to fund. GAO recommends that IRS re-establish goals for improving voluntary compliance and develop and document a strategy that outlines how it will use its data to update compliance strategies to address the tax gap. IRS disagreed with GAO's recommendation on establishing goals and agreed with the recommendation on compliance strategies. GAO continues to believe that goals are essential for results-oriented management.