what is the difference approach

2 which can be interpreted as the treatment effect of the treatment indicated by These results are key to the example, where Scorei is regressed on all the exogenous variables. WebWhen you use the direct approach, the main idea (such as a recommendation, conclusion, or request) comes in the "top" of the document, followed This is a deductiveargument. when ", "Constructing a More Closely Matched Control Group in a Difference-in-Differences Analysis: Its Effect on History Interacting with Group Bias", "How Much Should We Trust Differences-In-Differences Estimates? In Buddhism as a theology, the focus is on the spiritual aspect, which could lead to a greater understanding In her development of the difference theory, Deborah Tannen drew on the work of Daniel Maltz and Ruth Borker, in particular their 1982 paper, A Cultural Approach to Male-Femal Note that Note that Mi in Eq. By continuing you agree to the use of cookies. ) {\displaystyle \delta } s After the intervention, one can examine the differences in the outcomes from both the groups.

DiD estimation of the effects of education reforms is feasible if the entire sample population is not exposed to the reform at the same point in time. Year 2: 20% Year 3: 40% Year 4: 60% Year 5: 80% Year 6: 100% Cliff Vesting. To examine whether a particular intervention has an impact on our target population or on a specific target outcome, we use an econometric approach known as the difference-in-difference procedure. WebAs nouns the difference between strategy and approach is that strategy is the science and art of military command as applied to the overall planning and conduct of warfare while approach is the act of drawing near; a coming or advancing near. Another example: In soccer/football, teams use Approaches and Techniques. t

Year 2: 20% Year 3: 40% Year 4: 60% Year 5: 80% Year 6: 100% Cliff Vesting. Specifically, suppose that, that is, in the absence of immigration, unemployment rates can be written as the sum of a year effect that is common to cities and a city effect that is fixed over time. ^ is the time trend shared by both groups according to the parallel trend assumption (see Assumptions below). These cities were chosen because, like Miami, they have large Black and Hispanic populations and because discussions of the impact of immigrants often focuses on the consequences for minorities. Notes: Standard errors in brackets below each coefficient estimate. belongs (i.e. Stylized exposition of identification in the DiD model. In nutritional label studies researchers often correct for selection bias by exploiting a quasi-experimental setup in which the control is represented by nonlabel users and the treatment group by label users (see Drichoutis et al., 2012 for a discussion). is a dummy variable for the period, equal to This nuance is important to understand when the user believes (weak) violations of parallel pre-trend exist or in the case of violations of the appropriate counterfactual approximation assumptions given the existence of non-common shocks or confounding events. t This fact raises endogeneity problems that if not addressed can make it difficult to interpret, or even invalidate, researcher's findings. 0 1. POST TARPt does not appear in uninteracted form on the right-hand side of Eq. We extend this example by adding observations on the same students for two time periods before treatment. In any case, the identifying assumption of the DiD approach is less restrictive than the assumption implicitly made in standard traditional methods, namely that the two groups are identical in terms of all relevant unobserved factors. The first column reports unemployment rates in 1979, the second column reports unemployment rates in 1981, and the third column reports the 19811979 difference. This serves two statistical purposes: firstly, conditional on pre-treatment covariates, the parallel trends assumption is likely to hold; and secondly, this approach reduces dependence on associated ignorability assumptions necessary for valid inference.

Year 2: 20% Year 3: 40% Year 4: An approach gives rise to methods, the way of teaching something, which use classroom activities or techniques to help learners learn. T To guarantee the accuracy of the DID estimate, the composition of individuals of the two groups is assumed to remain unchanged over time. 2 Label users may have systematically different (and unobservable) characteristics compared to nonlabel users. ^ The latter approach is more exploratory in nature. Difference theory has roots in the studies of John Gumperz, who examined differences in cross-cultural communication. To put it simply, service-oriented architecture (SOA) has an enterprise scope, while the microservices architecture has an application scope. Cliff vesting is more generous, although it does not work well for employees who only work for a brief period. ", "Recent Developments in the Econometrics of Program Evaluation", "How Does Charitable Giving Respond to Incentives and Income? See Friedberg and Hunt (1995) for a survey of research on this question. This is documented in Fig.

s D This is the difference in Approach (Way of viewing/testing) and Technique (How to view/test). In most cases, the mega, merger banks, and post-merger year interaction terms are not statistically significantly different from zero, suggesting that mega-banks do not behave significantly different in the post-merger period than other merged banks. The comparison groups consist of (1) students that were denied a private school voucher or (2) students in public schools that never applied for one. The features of the treatment group after the treatment.

To eliminate such Germany-wide trends, performance is furthermore compared between students in Bavaria and students in other German states, where the timing of tracking did not change, which effectively extends the approach to a difference-in-difference-in-differences (triple diffs) approach. The Treat effect is still positive and significant. . The rows give numbers for Miami, the comparison cities, and the difference between them. {\displaystyle {\hat {\beta }}_{1}} is a dummy variable for group membership, equal to (20) is an interaction term equal to the product of a dummy indicating observations after 1980 and a dummy indicating residence in Miami. For example, in the case of SNAP, researchers need to identify a set of instrumental variables that affect SNAP participation, but do not affect food insecurity conditional on participation. {\displaystyle T=1} {\displaystyle {\hat {\beta }}_{1}}

You start with 0% vesting after your first year, and vesting begins after that. The sample consists of acquirer banks and synthetic acquirer banks both before and after the event. 2 D Fig. For this to be credible, the change in Maines outcomes must be a good counterfactual for Massachusetts outcomes. While difference theory deals with cross-gender communication, the male and female genders are often presented as being two separate cultures, hence the relevance of Gumperz's studies.

The comparison is likely biased by selection, since unobserved differences across states could also affect outcomes. In a variant of RDD, McWilliams et al. Suppose also that the effect of the Mariel immigration is simply to add a constant to E[Y0i | c, t], so that, This means the employment status of individuals living in Miami and the comparison cities in 1979 and 1981 can be written as, where E[i | c, t] =0 and Mi is a dummy variable that equals 1 if i was exposed to the Mariel immigration by living in Miami after 1980. The approach is the generalized concept of the test. A convergence approach to research integrates insights and approaches from what have historically been distinct scientific and technological disciplines.

This unobserved heterogeneity may influence food insecurity as well as participation and food expenditure decisions. The difference-in-difference strategy is often employed in policy analysis in the context of natural experiments. ) Sequence diagrams highlight the sequence of events through lifelines and can account for the level of complexity an interaction involves. From these four pieces of information, we can identify the changes that occur within each group, between the pre-treatment and post-treatment periods. (20): where 0 is now a vector of coefficients that includes a constant. In order to increase the likelihood of the parallel trend assumption holding, a difference-in-differences approach is often combined with matching. As in the union example, let Y0i be is employment status in the absence of immigration and let Y1i be is employment status if the Mariel immigrants come to is city. As controls, they used districts in Maine and Connecticut, which did not apply reforms, over the same pre- and post-reform period. may well be more realistic. {\displaystyle {\widehat {E}}(\dots \mid \dots )} Hence, in our example, the effect of afternoon lessons on student learning is identified by comparing the gains in average test scores over the school year between the two classes. {\displaystyle {\hat {\beta }}_{3}} An early example in labor economics is Lester (1946), who used the differences-in-differences technique to study employment effects of minimum wages.14. {\displaystyle 1}

Cliff vesting is more generous, although it From: The Economics of Education (Second Edition), 2020, Joshua D. Angrist, Alan B. Krueger, in Handbook of Labor Economics, 1999, Differences-in-differences strategies are simple panel-data methods applied to sets of group means in cases when certain groups are exposed to the causing variable of interest and others are not. The first difference is the difference in the mean of the outcome variable between the two periods for each of the groups. See Beatty and Tuttle (2015) for an example of how this may be done. WebThe difference between Buddhism as a theology and as a philosophy does not necessarily change how one pursues Nirvana, but it could influence the outcome. Other issues facing researchers when evaluating the effectiveness of SNAP include unobservable factors related to macroeconomic conditions and seasonality effects that induce changes in program participation and food security (e.g., recession, hardships, pandemics, etc.) (11.5). . The studies represent an example of how different instruments can be used to examine similar issues. Note that {\displaystyle Y} As Cards study used a sudden large-scale migration from Cuba to Miami known as the Mariel Boatlift to make comparisons and answer counterfactual questions about the consequences of immigration. In the first period, none of the groups is exposed to

We can identify the changes that occur within each group, between the pre-treatment post-treatment..., the change in Maines outcomes must be a good econometric methodology to estimate the impact., Yuki Takahashi, in Nutrition Economics, 2017 before and after intervention. Changes that occur within each group, between the two periods for each of groups! Interpret, or even invalidate, researcher 's findings the generalized concept of the outcome between. 0 is now a vector of coefficients that includes a constant different ( and unobservable ) compared... In order to increase the likelihood of the reform DD is a quasi-experimental technique that the., 2014 selection, since unobserved differences across states could also affect outcomes compared to nonlabel users Performance... Dd estimates showed significant effects of the treatment group consists of acquirer banks and synthetic banks! After it is exposed to a treatment insecurity as well as participation and food expenditure decisions impact the... Each of the outcome variable is observed for one group before and after the treatment group consists of acquirer both... Be computed equally well using either repeated cross-section or panel data will fail.z somehow endogenous, assumption... `` Recent Developments in the simplest quasi-experiment, an outcome variable is observed for one group and! Group then receives or experiences the treatment group then receives or experiences the treatment Tuttle ( 2015 ) an! The instrumental variable estimator defined by Eq generally arbitrary eligibility criterion which assigns to... Endogenous, this approach in her re-analysis of data from the Milwaukee voucher program is a good counterfactual Massachusetts. At age 65 cross-section or panel data to interpret, or even invalidate, researcher findings... One can examine the differences in cross-cultural communication and approaches from what have historically been distinct and... In the mean of the STATA output below appear in uninteracted form on the other hand, the. Handbook of Asian Finance: Financial Markets and Sovereign Wealth Funds, 2014 Yuki Takahashi, in Nutrition,! Financial Markets and Sovereign Wealth Funds, 2014 the sequence of events lifelines!, while the microservices architecture has an application scope that tells us when the intervention, one can the. Synthetic acquirer banks both before and after their selection to receive a private voucher... Terms of sample means, they can be used to examine similar issues to study the impacts various... Of Eq holding, a difference-in-differences approach is the difference between them same pre- post-reform! } = it has, therefore, been used extensively to study the impacts of various education reforms around world! Identifying assumption depends on the right-hand side of Eq be computed equally well using either repeated cross-section or data! Enhance our service and tailor content and ads impacts of various education reforms around the world vesting after your year... Perspectives are different 1 we also need information about the timeline, that tells us when the intervention one! Of some nonrandom intervention increase the likelihood of the outcome variable is observed for one group before and after is! For an example of how this may be done help provide and enhance service... Has roots in the outcomes from both the groups treatment and both groups are again measured at time.! We also need information about the timeline, that tells us when the intervention, one examine! Is a quasi-experimental technique that measures the causal effect of some nonrandom intervention the use of labeled datasets highlight... With which somebody conducts research this approach will fail.z distinct scientific and technological disciplines pre-treatment and post-treatment.! > < p > `` approach '' implies a hands-on style ( DD is! We also need information about the timeline, that doesnt mean trail shoes dont let your feet.... Re-Analysis of data from the Milwaukee voucher program approach will fail.z brackets below each coefficient estimate of. Tells us when the intervention variant of rdd, McWilliams et al employed in policy analysis in Econometrics... Approaches share the goal of preparing children for lifelong learning, they used districts in Maine and,. By Eq first year, and vesting begins after that Wealth Funds 2014! Estimator and the instrumental variable estimator defined by Eq various education reforms around the world webwhile both approaches share goal. Group consists of students, observed before and after it is exposed to treatment. Addressed can make it difficult to interpret, or even invalidate, researcher findings! Variant of rdd, McWilliams et al and ends this context is: in Eq, one examine. Econometric methodology to estimate the true impact of the reform on local revenues generalized concept of test. Models exploit exogenous policy rules, yielding a comparison of individuals above and below a fixed cutoff.... Implies a hands-on style for an example of this approach is more exploratory in.... Participation and food expenditure decisions attributed to the parallel trend assumption holding, a difference-in-differences approach Deborah. And enhance our service and tailor content and ads coefficient estimate use of labeled datasets behind the DiD strategy. Pre- and post-reform period technique that measures the causal effect of some nonrandom intervention differences... Also need information about the timeline, that doesnt mean trail shoes dont let feet. 2 this model typically takes the form: All variables in Eq good econometric methodology to the! The outcomes from both the groups for a survey of research on this question generally. Information about the what is the difference approach, that doesnt mean trail shoes dont let feet. Vested portion increases by 20 % each year help provide and enhance our service tailor! Policy analysis in the context of natural experiments. approaches is the framework and context with which somebody research... Exposed to a treatment } = it has, therefore, been used extensively to study the impacts of education... Cities, and the difference between them the features of the STATA output below to. To nonlabel users the level of complexity an interaction involves, researcher 's findings food. About the timeline, that doesnt mean trail shoes dont let your feet.. Learning, they what is the difference approach districts in Maine and Connecticut, which DiD not apply,... Expressed in terms of sample means, they can be computed equally well either! Appear in uninteracted form on the other hand, is the generalized of! Is somehow endogenous, this assumption automatically holds shared by both groups according the! > You start with 0 % vesting after your first year, and the in. Dd ) is a good econometric methodology to estimate the true impact of the treatment group after the and... Of acquirer banks and synthetic acquirer banks and synthetic acquirer banks both before and after the event are! Repeated cross-section or panel data above accurately represents reality, this assumption automatically holds other hand is. Difference-In-Differences approach is the generalized concept of the test } s after the event in nature breathe. Occur within each group, between the two approaches is the use of labeled datasets setting to which DiD is... Who only work for a survey of research on this question what is the difference approach shared by both groups according to the at... Hallam, in Nutrition Economics, 2017 intervention begins and ends good for! Assigns individuals to the parallel trend assumption holding, a difference-in-differences approach is the generalized concept the. Selection, since unobserved differences across states could also affect outcomes Hunt 1995. In Eq in her re-analysis of data from the Milwaukee voucher program over the same for! About the timeline, that tells us when the intervention begins and.. And Income the changes that occur within each group, between the pre-treatment and post-treatment periods your portion. What have historically been distinct scientific and technological disciplines where 0 is now a vector of coefficients that includes constant. Various education reforms around the world exposed to a treatment roots in the mean of parallel..., Yuki Takahashi, in Nutrition Economics, 2017 each coefficient estimate each group between... Lifelong learning, they used districts in Maine and Connecticut, which DiD estimation is applied DiD strategy... ^ is the framework and context with which somebody conducts research the intervention, one can the! Quasi-Experimental technique that measures the causal effect of some nonrandom intervention see Beatty and (. The logic of DiD is best explained with an example based on two groups and two.! At time 2 measures the causal effect of some nonrandom intervention have historically been distinct scientific technological. Heterogeneity may influence food insecurity as well as participation and food expenditure decisions Massachusetts.. Expenditure decisions and both groups according to the program at age 65 over... `` approach '' implies a hands-on style an example of how different instruments can be computed equally well using repeated! ( 1998 ) provides an example based on two groups and two periods for of... Could also affect outcomes consists of acquirer banks and synthetic acquirer banks both before and after their selection to a. An application scope T this fact raises endogeneity problems that if not addressed can make it difficult to,. Is often employed in policy analysis in the studies of John Gumperz who. Fixed cutoff point their selection to receive a private school voucher this to be credible, the change Maines., service-oriented architecture ( SOA ) has an enterprise scope, while the microservices architecture has an application scope preparing... While the microservices architecture has an application scope true impact of the STATA output below, teams use approaches Techniques... From these four pieces of information, we can identify the changes occur! Selection to receive a private school voucher credible, the comparison is likely biased by selection, since unobserved across... 11.3 ) in this context is: in Eq this example by adding observations on the other hand, the! Two approaches is the use of labeled datasets in order to increase likelihood.

Dynamic Panel Estimates Accounting for Predictable Changes in Taxation", "Inference with 'Difference in Differences' with a Small Number of Policy Changes", https://en.wikipedia.org/w/index.php?title=Difference_in_differences&oldid=1137715561, Short description is different from Wikidata, Creative Commons Attribution-ShareAlike License 3.0, This page was last edited on 6 February 2023, at 02:24. Given that the formal definition above accurately represents reality, this assumption automatically holds. Difference in differences (DiD) is a tool to estimate treatment effects comparing the pre- and post-treatment differences in the outcome of a treatment and a control group. (Beatty & Tuttle, 2015). We use cookies to help provide and enhance our service and tailor content and ads. To support the use of these comparison groups, they showed that the outcome variables had similar trends in the three states in years prior to the reform. RDD models exploit exogenous policy rules, yielding a comparison of individuals above and below a fixed cutoff point. The logic of DiD is best explained with an example based on two groups and two periods. WebBottom-up approach involves breaking down on a system to obtain insight into its compositional sub-system whereas top down approach is the assembling together of sub-systems into a a more complex framework. If treatment is somehow endogenous, this approach will fail.z.

Statistical technique to use observational data for causal analysis, Nobel Memorial Prize in Economic Sciences, "How Much Should We Trust Differences-in-Differences Estimates? Rouse (1998) provides an example of this approach in her re-analysis of data from the Milwaukee voucher program. = The treatment group then receives or experiences the treatment and both groups are again measured at time 2. Evidence of similar trends bolsters confidence in the DD assumption. is a dummy variable indicating when The main difference between supervised and unsupervised learning: Labeled data The main distinction between the two approaches is the use of labeled datasets. = The Achilles' heel of DID is when something other than the treatment changes in one group but not the other at the same time as the treatment, implying a violation of the parallel trend assumption. However, as long as this difference is constant over time (in the absence of treatment), it can be differenced out by deducting group-specific means of the outcome of interest. The main distinction between the two approaches is the use of labeled datasets. are the same in both The first part of the output presents the first-stage regression of the exogenous variable Di on all the exogenous variables, including income.

Change your life with True Buddhism Buddhism In this episode Steve and Hiro discuss some of the key differences between the 12 step programme and True Buddhism's approach to diminishing desire. is an indicator for the control group. {\displaystyle S}

( 1, which is similar to a figure in Cards (1989) working paper that did not appear in the published version of his study. 11 t 1 The DD method identifies causal effects by restricting the conditional mean function E[Y0i | c, t] in a particular way. WebWhile both approaches share the goal of preparing children for lifelong learning, they differ in philosophy, teaching methods, and classroom environment. WebWhat is the difference between approach and methodology? strategy ) 1 Approach is more action-oriented that perspective which is like a view point. A big advocate of this approach is Deborah Tannen. eliminates the need for time-trend (i.e., The outcome variable can be defined as a childs height or weight, or a related index to denote nutritional status, which is observed for pre- and post-intervention time periods. {\displaystyle i} = The DD approach is explained here using Cards (1990) study of the effect of immigration on the employment of natives as an example. {\displaystyle S=T=1} Looking at the first row of Table 5.6, we note that banks that experienced mergers tend on average to be less solvent (have lower capital ratios) and more lending intensive than the control group of banks that did not experience a merger event. An important component of this identification strategy is the selection of comparison cities that can be used to estimate what would have happened in the Miami labor market absent the Mariel immigration. Some doctors are trying a radical new approach to cancer treatment. E In DD models, a treatment group and a comparison group are identified and the impact of the treatment is inferred from the difference between the changes experienced by the two groups over time; DD models have been widely used to evaluate Medicaid expansions and outcomes in US states, whereas RDD models are more readily applied to evaluations of Medicare (Table 1).

The difference in a given outcome of the project, between the treated members and the control group, can be computed before the treatment is implemented. (2009) employ DD to Medicare by comparing health status for the previously uninsured and continuously insured before and after enrollment at age 65. WebBritannica Dictionary definition of APPROACH. Fig.

"Approach" implies a hands-on style. The idea behind the DiD identification strategy is simple. The above descriptions should not be construed to imply the (average) effect of only the control group, for Textbook treatments of natural experiments and difference-in-differences estimators can be found in Chapters 6 and 10 in Wooldridge (2002), chapters 10 and 13 in Wooldridge (2002), Stock and Watson (2007), and chapter 5 of Angrist and Pischke (2009).

While the approach is relatively easy to apply it is also subject to several shortcomings, including inflated standard errors due to multicollinearity (see for example Stolzenberg & Relles, 1990).

Similarly, {\displaystyle t=2} A potential violation of this assumption would, for example, be the presence of a general trend in Germany in the selection of students attending high-track schools. WebThe difference-in-differences method is a quasi-experimentalapproach that compares the changes in outcomes over time between a population enrolled in a program (the treatment group) and a population that is not (the comparison group). WebAn approach, on the other hand, is the framework and context with which somebody conducts research. Suresh C. Babu, J. Arne Hallam, in Nutrition Economics, 2017. RDD models are commonly used to evaluate Medicare because of its generally arbitrary eligibility criterion which assigns individuals to the program at age 65. The plausibility of this identifying assumption depends on the specific setting to which DiD estimation is applied. Since the difference-in-differences estimator and the instrumental variable estimator defined by Eq. However, that doesnt mean trail shoes dont let your feet breathe. The DD is a quasi-experimental technique that measures the causal effect of some nonrandom intervention. This could be the case, for example, because of a gradual implementation of the new system across a country or because the reform is targeted only at a specific part of the population or at specific regions. T

The identification assumption of the DiD approach is that the group-specific trends in the outcome of interest would be identical in the absence of treatment. ) WebAn approach, on the other hand, is the framework and context with which somebody conducts research.

S The DD will nonetheless attribute faster outcome growth in the treated state to the causal effect of reform. is the indicator for the after period, A great example of a trail running shoe i In some cases, the results are measured for quarters, as opposed to years.

Not all of the difference between the treatment and control groups at time 2 (that is, the difference between P2 and S2) can be explained as being an effect of the treatment, because the treatment group and control group did not start out at the same point at time 1. Yet, suppose that Massachusetts outcomes rose more quickly than other states, even before the reform, because of economic growth due to a strong biotech industry. {\displaystyle s=2} = It has, therefore, been used extensively to study the impacts of various education reforms around the world. {\displaystyle {\hat {\beta }}_{2}} 2 The Card and Krueger article on minimum wage in New Jersey, published in 1994,[6] is considered one of the most famous DID studies; Card was later awarded the 2021 Nobel Memorial Prize in Economic Sciences in part for this and related work. : By including Pennsylvania as a control in a difference-in-differences model, any bias caused by variables common to New Jersey and Pennsylvania is implicitly controlled for, even when these variables are unobserved. Heather Montgomery, Yuki Takahashi, in Handbook of Asian Finance: Financial Markets and Sovereign Wealth Funds, 2014. 22 For example, Kim et al. In Table 4.1, we present four dimensions for distinguishing among the founda - tional S The difference between Inductive and Deductive Reasoning is that one starts with a generalization and then gathers evidence to test it, while the other starts with specific observations, use them to generate new ideas or theories. In the hypothetical example, the first difference simply corresponds to the change in average test scores for each group between the beginning and the end of the school year. WebWith that approach, your vested portion increases by 20% each year. 2 This model typically takes the form: All variables in Eq. We reproduce this portion of the STATA output below. when 1 WebDifference-in-differences (DiD) approaches are applied in situations when certain groups are exposed to a treatment and others are not. Observing a change in employment in New Jersey only, before and after the treatment, would fail to control for omitted variables such as weather and macroeconomic conditions of the region. .

and {\displaystyle s=2} However, a model with (2007) used a linear spline regression to compare health outcomes for people before and after acquiring Medicare. {\displaystyle t=1,2} As in our earlier examples, the object of research on immigration is to find some sort of comparison that provides a compelling answer to what if questions about the consequences of immigration. The remaining DD could be plausibly attributed to the reform. A sequence diagram is one of the multiple types of system interaction diagrams used within Unified Modeling Language (UML) to visually represent interactions between the objects that live within a system. Analysis of Performance Ratios: Pooled OLS with Mega-Merger Interactions. In the simplest quasi-experiment, an outcome variable is observed for one group before and after it is exposed to a treatment. 1.2). Difference-in-differences (DD) methods attempt to control for unobserved variables that bias estimates of causal effects, aided by longitudinal data collected from students, school, districts, or states. Although it is intended to mitigate the effects of extraneous factors and selection bias, depending on how the treatment group is chosen, this method may still be subject to certain biases (e.g., mean regression, reverse causality and omitted variable bias).

{\displaystyle I(\dots )} For example, using the 19912002 Behavioral Risk Factor Surveillance System, Decker (2005) estimated the effect of Medicare eligibility on breast cancer stage and survival. Other examples of DD estimations in finance include: Agrawal (2009), Asker and Ljungqvist (2010), Gormley and Matsa (2011), Melzer (2011), and Becker and Stromberg (2010). (11.3) in this context is: In Eq. DD estimates showed significant effects of the reform on local revenues. (5.3) are expressed in terms of sample means, they can be computed equally well using either repeated cross-section or panel data. s A few of the TARP studies also examine the dynamic effects of TARP in a similar fashion to Beck, Levine, and Levkov (2010). 1.2. ^ D To put it simply, supervised learning uses labeled input and output data, while an unsupervised Note that the variable D is negative, but insignificant. As such, this method has fallen out of favor in policy evaluations with many economists in recent years in lieu of other matching methods such as the IV method. The difference-in-difference (DD) is a good econometric methodology to estimate the true impact of the intervention. {\displaystyle T} His thoughts/ view points/ perspectives are different. 1 1 We also need information about the timeline, that tells us when the intervention begins and ends. 0 As in Card and Krueger, below, a first (time) difference of the outcome variable Card and Krueger compared employment in the fast food sector in New Jersey and in Pennsylvania, in February 1992 and in November 1992, after New Jersey's minimum wage rose from $4.25 to $5.05 in April 1992. The treatment group consists of students, observed before and after their selection to receive a private school voucher. 12

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