Chetty, et al. on the American Statistical Association’s Recent Position Statement on Value-Added Models (VAMs): Five Points of Contention
by Margarita Pivovarova, Jennifer Broatch & Audrey Amrein-Beardsley - August 01, 2014
Over the last decade, teacher evaluation based on value-added models (VAMs) has become central to the public debate over education policy. In this commentary, we critique and deconstruct the arguments proposed by the authors of a highly publicized study that linked teacher value-added models to students’ long-run outcomes, Chetty et al. (2014, forthcoming), in their response to the American Statistical Association statement on VAMs. We draw on recent academic literature to support our counter-arguments along main points of contention: causality of VAM estimates, transparency of VAMs, effect of non-random sorting of students on VAM estimates and sensitivity of VAMs to model specification.
Recently, the authors of a highly publicized and cited study that linked teacher value-added estimates to the long-run outcomes of their students (Chetty, Friedman, & Rockoff, 2011; see also Chetty, et al., in press I, in press II) published a point-by-point discussion of the Statement on Using Value-Added Models for Educational Assessment released by the American Statistical Association (ASA, 2014). This once again brought the value-added model (VAM) and its use for increased teacher and school accountability to the forefront of heated policy debate.
In this commentary we elaborate on some of the statements made by Chetty, et al. (2014). We position both the ASAs statement and Chetty, et al.s (2014) response within the current academic literature. As well, we deconstruct the critiques and assertions advanced by Chetty, et al. (2014) by providing counter-arguments and supporting them by the scholarly research on this topic.
In doing so, we rely on the current research literature that has really been done on this subject over the past ten years. This more representative literature was completely overlooked by Chetty, et al. (2014), even though, paradoxically, they criticize the ASA for not citing the recent literature appropriately themselves (p. 1). With this being our first point of contention, we also discuss four additional points of dispute within the commentary.
POINT 1: MISSING LITERATURES
In their critique of the ASA statement, posted on a university-sponsored website, Chetty, et al. (2014) marginalize the current literature published in scholarly journals on the issues surrounding VAMs and their uses for measuring teacher effectiveness. Rather, Chetty et al. cite only works representing econometricians scholarly pieces, apparently in support of their a priori arguments and ideas. Hence, it is important to make explicit the rather odd and extremely selective literature Chetty, et al. included in the reference section of their critique, on which Chetty, et al. relied "to prove" some of the ASAs statements incorrect. The whole set of peer-reviewed articles that counter Chetty, et al.s arguments and ideas are completely left out of their discussion.
A search on the Educational Resources Information Center (ERIC) with value-added as key words for the same last five years yields 406 entries, and a similar search in Journal Storage (JSTOR, a shared digital library) returns 495. Chetty, et al., however, only cite 13 references to critique the ASAs statement, one of which was the actual statement itself, leaving 12 external citations in total and in support of their critique. Of these 12 external citations, three are references to their two forthcoming studies and a replication of these studies methods; three have thus far been published in peer-reviewed academic journals, six were written by their colleagues at Harvard University; and 11 were written by teams of scholars with economics professors/econometricians as lead authors.
POINT 2: CORRELATION VERSUS CAUSATION
The second point of contention surrounds whether the users of VAMs should be aware of the fact that VAMs typically measure correlation, not causation. According to the ASA, as pointed out by Chetty, et al. (2014), effects positive or negativeattributed to a teacher may actually be caused by other factors that are not captured in by the model (p. 2). This is an important point with major policy implications. Seminal publications on the topic, Rubin, Stuart and Zanutto (2004) and Wainer (2004) who positioned their discussion within the Rubin Causal Model framework (Rubin, 1978; Rosenbaum and Rubin, 1983; Holland, 1986), clearly communicated, and evidenced, that value-added estimates cannot be considered causal unless a set of "heroic assumptions" are agreed to and imposed. Moreover, anyone familiar with education will realize that this [is]...fairly unrealistic (Rubin, et al. 2004, p. 108). Instead, Rubin, et al. suggested, given these issues with confounded causation, we should switch gears and evaluate interventions and reward incentives as based on the descriptive qualities of the indicators and estimates derived via VAMs. This point has since gained increased consensus among other scholars conducting research in these areas (Amrein-Beardsley, 2008; Baker, et al., 2010; Betebenner, 2009; Braun, 2008; Briggs & Domingue, 2011; Harris, 2011; Reardon & Raudenbush, 2009; Scherrer, 2011).
POINT 3: THE NON-RANDOM ASSIGNMENT OF STUDENTS INTO CLASSROOMS
The third point of contention pertains to Chetty, et al.s statement that recent experimental and quasi-experimental studies have already solved the causation versus correlation issue. This claim is made despite the substantive research that evidences how the non-random assignment of students constrains VAM users capacities to make causal claims.
The authors of the Measures of Effective Teaching (MET) study cited by Chetty, et al. in their critique, clearly state, we cannot say whether the measures perform as well when comparing the average effectiveness of teachers in different schools&given the obvious difficulties in randomly assigning teachers or students to different schools (Kane, McCaffrey, Miller & Staiger, 2013, p. 38). VAM estimates were found to be biased for teachers who taught more relatively homogenous sets of students with lower levels of prior achievement, despite the levels of sophistication in the statistical controls used (Hermann, Walsh, Isenberg, & Resch, 2013; see also Ehlert, Koedel, Parsons, & Podgursky, 2014; Guarino et al., 2012).
Researchers repeatedly demonstrated that non-random assignment confounds value-added estimates independent of how many sophisticated controls are added to the model (Corcoran, 2010; Goldhaber, Walch, & Gabele, 2012; Guarino, Maxfield, Reckase, Thompson, & Wooldridge, 2012; Newton, Darling-Hammond, Haertel, & Thomas, 2010; Paufler & Amrein-Beardsley, 2014; Rothstein, 2009, 2010).
Even in experimental settings, it is still not possible to distinguish between the effects of school practice, which is of interest to policy-makers, and the effects of school and home context. There are many factors at the student, classroom, school, home, and neighborhood levels that would confound causal estimates that are beyond researchers control. Thus, the four experimental studies cited by Chetty, et al. (2014) do not provide ample evidence to refute the ASA on this point.
POINT 4: ISSUES WITH LARGE-SCALE STANDARDIZED TEST SCORES
In their position statement, ASA authors (2014) rightfully state that the standardized test scores used in VAMs should not be the only outcomes of interest for policy makers and stakeholders. Indeed, current agreement is that test scores might not even be one of the most important outcomes capturing a students educated self. Also, if value-added estimates from standardized test scores cannot be interpreted as causal, then the effect of high value-added teachers on college attendance, earnings, and reduced teenage birth rates cannot be considered causal either as opposed to what is implied by Chetty, et al. (2011; see also Chetty, et al., in press I, in press II).
Ironically, Chetty, et al. (2014) cite Jacksons (2013) study to confirm their point that high value-added teachers also improve long-run outcomes of their students. Jackson (2013), however, actually found that teachers who are good at boosting test scores are not always the same teachers who have positive and long-lasting outcomes on non-cognitive skills acquisition. Moreover, value-added as related to test scores and non-cognitive outcomes for the same teachers were then, and have since been shown to be, weakly correlated with one another.
POINT 5: MODEL SPECIFICITY
Lastly, ASA (2014) expressed concerns about the sensitivity of value-added estimates to model specifications. Recently, researchers have found that value-added estimates are highly sensitive to the tests being used, even within the same subject areas (Papay, 2011) and the different subject areas taught by the same teachers given different student compositions (Loeb & Candelaria, 2012; Newton, et al., 2010; Rothstein, 2009, 2010). While Chetty, et al. rightfully noted that different VAMs typically yield correlations around r = 0.9, this is typical with most garbage in, garbage out models. These models are too often used, too often without question, to process questionable input and produce questionable output (Banchero & Kesmodel, 2011; Gabriel & Lester, 2012, 2013; Harris, 2011).
What Chetty, et al. overlooked, though, are the repeatedly demonstrated weak correlations between value-added estimates and other indicators of teacher quality, on average between r = 0.3 and 0.5 (see also Corcoran, 2010, Goldhaber et al., 2012; McCaffrey, Sass, Lockwood, & Mihaly, 2009; Broatch and Lohr, 2012; Mihaly, McCaffrey, Staiger, & Lockwood, 2013).
In sum, these are only a few points from this point-by-point discussion that would strike anyone even fairly familiar with the debate over the use and abuse of VAMs. These points are especially striking given the impact Chetty, et al.s original (2011) study and now forthcoming studies (Chetty, et al., in press I, in press II) have already had on actual policy and the policy debates surrounding VAMs. Chetty, et al.s (2014) discussion of the ASA statement, however, should cause others pause in terms of whether in fact Chetty, et al. are indeed experts in the field, or not. What certainly has become evident is that they do not have their minds wrapped around the extensive set of literature or knowledge on this topic. If they had, they may not have come off as so selective, as well as biased, citing only those representing certain disciplines and certain studies to support certain assumptions and facts upon which their criticisms of the ASA statement were based.
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