Teachers: The Major Players in Education - Visible Learning for Teachers - PDF

CHAPTER 3 1...

CHAPTER 3 1 2 3 Teachers: the major 4 5 6 players in the 7 8 9 education process 10 1 2 3 4 5 6 It might have seemed more obvious to start with the students, but that would not be the 7 correct place to start! We so often make claims about students, their learning styles, their 8 attitudes, their love or not of schooling, their families and backgrounds, and their culture. 9 In so many cases, this discussion is about why we can or cannot have an effect on their 20 learning. 1 We so often worry about who students are.While it is the case that the largest source 2 of variance in learning outcomes is attributable to the students, this should not mean that 3 we stop at what students can and cannot do.We invent so many ways in which to explain 4 why students cannot learn: it is their learning styles; it is right or left brain strengths or 5 deficits; it is lack of attention; it is their refusal to take their medication; it is their lack of 6 motivation; it is their parents not being supportive; it is because they do not do their work, 7 and so on. It is not that these explanations are wrong (although some are – there is no 8 support for learning styles, for example) or right (parental expectations and encouragement 9 are powerful factors), but the underlying premise of most of these claims is the belief that 30 we, as educators, cannot change the student. It is this belief that is at the root of deficit 1 thinking.The belief that background factors have the strongest influence on learning would 2 Copyright © 2014. Taylor and Francis. All rights reserved. be an argument for putting more resources into poverty and home programs rather than 3 into schooling. We must consider ourselves positive change agents for the students who 4 come to us – for most, it is compulsory that they come to school and sometimes they 5 come reluctantly, but mostly (at least initially) students are eager to be challenged into 6 learning. My point is that teachers’ beliefs and commitments are the greatest influence on 7 student achievement over which we can have some control – and this book outlines these beliefs 8 and commitments. 9 We so often worry about what teachers do. It would be easy to say that it is ‘teachers 40 who make the difference’.This is, indeed, not the case being made in this book.There are 1 just as many teacher influences below d = 0.40 as there are above, and in most school 2 systems there is more variance within a school than between schools.This within-school 3 variance highlights the variance provided by teacher effects, and while we may wish to 4 believe that all of our teachers are excellent, this is not always the view of those who have 5 been their students. Rather, there are some teachers doing some things that make the 61 22 Hattie, J. (2014). Visible learning for teachers. Retrieved from http://ebookcentral.proquest.com/lib/spu/detail.action?docID=958163 Created from spu on 2017-06-12 15:16:58.  Teachers: the major players in the education process 1 difference.The effect of high-effect teachers compared with low-effect teachers is about 2 d = 0.25, which means that a student in a high-impact teacher’s classroom has almost a 3 year’s advantage over his or her peers in a lower-effect teacher’s classroom (Slater, Davies, 4 & Burgess, 2009).A major claim in this chapter is that the differences between high-effect 5 and low-effect teachers are primarily related to the attitudes and expectations that 6 teachers have when they decide on the key issues of teaching – that is, what to teach and 7 at what level of difficulty, and their understandings of progress and of the effects of their 8 teaching. It is some teachers doing some things with a certain attitude or belief system 9 that truly makes the difference. This brings me to the first set of attributes that relate to 10 ‘visible learning inside’: passionate and inspired teachers. 1 We start with the teachers’ and school leaders’ mind frames. For example, Sam Smith 2 (2009) introduced a very powerful target-setting program in a large urban high school, 3 and many of the teachers refused to participate, claiming that they were not responsible 4 for whether students met targets or not: ‘If they did not do their homework, failed to 5 complete assignments, did not attend class, then why should teachers be held responsible 6 for students meeting targets?’The teachers argued that teacher targets were related more 7 to ensuring coverage of the curriculum, providing worthwhile resources and activities, 8 and ensuring order and fairness in the classroom. 9 Russell Bishop (2003) has provided one of the most effective interventions available 20 for minority students in mainstream classrooms and he starts with the beliefs of teachers. 1 He argued that teachers come into classrooms with very strong theories about students 2 and often resist evidence that their students do not conform to these theories. These 3 teachers have theories about race, culture, learning, development, and students’ levels of 4 performance and rates of progress. One of the first acts in Bishop’s intervention is to survey 5 students’ views on these matters. He then shows the teachers the difference between the 6 students’ beliefs and the teachers’ own. Only then can Bishop start the intervention, which 7 is about teachers’ beliefs, first and foremost. 8 9 30 VISIBLE LEARNING – CHECKLIST FOR INSPIRED AND PASSIONATE TEACHING 1 2 1. All adults in this school recognize that: Copyright © 2014. Taylor and Francis. All rights reserved. 3 a. there is variation among teachers in their impact on student learning and achievement; 4 b. all (school leaders, teachers, parents, students) place high value on having major 5 positive effects on all students; and 6 c. all are vigilant about building expertise to create positive effects on achievement for 7 all students. 8 9 40 1 2 3 4 5 61 23 Hattie, J. (2014). Visible learning for teachers. Retrieved from http://ebookcentral.proquest.com/lib/spu/detail.action?docID=958163 Created from spu on 2017-06-12 15:16:58.  The source of ideas and the role of teachers The case for the passionate, inspired teacher 1 2 3 4 VISIBLE LEARNING – CHECKLIST FOR INSPIRED AND PASSIONATE TEACHING 5 6 2. This school has convincing evidence that all of its teachers are passionate and inspired – 7 and this should be the major promotion attribute of this school. 8 9 10 One of the more exciting periods of my research work was when I was at the University 1 of North Carolina working with Richard Jaeger, Lloyd Bond, and many others on the 2 technical issues relating to the National Board for Professional Teaching Standards 3 (NBPTS). Laurence Ingvarson and I recently edited a book about this exciting time, and 4 the breakthroughs in performance assessment in education, the development of scoring 5 rubrics, and the psychometrics relating to these issues that have truly changed our way of 6 looking at teachers, classrooms, and identification of excellence (see Ingvarson & Hattie, 7 2008). The NBPTS is still, in my estimation, the best system for dependably identifying 8 excellent teachers, although there is still much to do to improve it. Using multiple indicators 9 of the effect of teachers on students, moving away from evaluating the correlates as opposed 20 to the actual effects on students, and making sure that the evaluation methods are also 1 excellent professional development is at the heart of the NBPTS model. This chapter, 2 however, is not a review of the NBPTS, because there are other sources and websites that 3 can provide this background. Instead, one study is highlighted that underlines the 4 importance of passionate and inspired teachers. 5 Richard Jaeger and I started by reviewing the literature (in the more traditional way 6 than that used when undertaking a meta-analysis) on the distinctions between expert and 7 experienced teachers, rather than using the more usual distinction between experienced 8 and novice teachers.We sent our findings to many of the pre-eminent researchers in this 9 field, and to expert teachers, for their comment, changes, and input.We identified five major 30 dimensions of excellent, or ‘expert’, teachers. Expert teachers have high levels of knowledge 1 and understanding of the subjects that they teach, can guide learning to desirable surface 2 Copyright © 2014. Taylor and Francis. All rights reserved. and deep outcomes, can successfully monitor learning and provide feedback that assists 3 students to progress, can attend to the more attitudinal attributes of learning (especially 4 developing self-efficacy and mastery motivation), and can provide defensible evidence of 5 positive impacts of the teaching on student learning. Herein lies the differences between 6 the terms ‘expert’ and ‘experienced’. 7 8 9 VISIBLE LEARNING – CHECKLIST FOR INSPIRED AND PASSIONATE TEACHING 40 1 3. This school has a professional development program that: 2 a. enhances teachers’ deeper understandings of their subject(s); 3 b. supports learning through analyses of the teachers’ classroom interactions with 4 students; 5 61 24 Hattie, J. (2014). Visible learning for teachers. Retrieved from http://ebookcentral.proquest.com/lib/spu/detail.action?docID=958163 Created from spu on 2017-06-12 15:16:58.  Teachers: the major players in the education process 1 2 c. helps teachers to know how to provide effective feedback; 3 d. attends to students’ affective attributes; and 4 e. develops the teacher’s ability to influence students’ surface and deep learning. 5 6 7 8 a. Expert teachers can identify the most important ways in 9 which to represent the subject that they teach 10 1 In Visible Learning, it was shown that teachers’ subject-matter knowledge had little effect 2 on the quality of student outcomes! The distinction, however, is less the ‘amount’ of 3 knowledge and less the ‘pedagogical content knowledge’, but more about how teachers 4 see the surface and the deeper understandings of the subjects that they teach, as well as 5 their beliefs about how to teach and understand when students are learning and have 6 learned the subject. Expert teachers and experienced teachers do not differ in the amount 7 of knowledge that they have about curriculum matters or knowledge about teaching 8 strategies – but expert teachers do differ in how they organize and use this content 9 knowledge. Experts possess knowledge that is more integrated, in that they combine the 20 introduction of new subject knowledge with students’ prior knowledge; they can relate 1 current lesson content to other subjects in the curriculum; and they make lessons 2 uniquely their own by changing, combining, and adding to the lessons according to their 3 students’ needs and their own teaching goals. 4 As a consequence of the way in which they view and organize their approach, expert 5 teachers can quickly recognize sequences of events occurring in the classroom that in some 6 way affect the learning and teaching of a topic.They can detect and concentrate more on 7 information that has most relevance, they can make better predictions based on their 8 representations about the classroom, and they can identify a greater store of strategies that 9 students might use when solving a particular problem.They are therefore able to predict 30 and determine the types of error that students might make, and thus they can be much 1 more responsive to students.This allows expert teachers to build understandings as to the 2 how and why of student success.They are more able to reorganize their problem-solving Copyright © 2014. Taylor and Francis. All rights reserved. 3 in light of ongoing classroom activities, they can readily formulate a more extensive range 4 of likely solutions, and they are more able to check and test out their hypotheses or 5 strategies.They seek negative evidence about their impact (who has not learnt, who is not 6 making progress) in the hurly-burly of the classroom, and use it to make adaptations and 7 to problem-solve. 8 These teachers maintain a passionate belief that students can learn the content and 9 understandings included in the learning intentions of the lesson(s).This claim about the 40 ability to have a deep understanding of the various relationships also helps to explain why 1 some teachers are often anchored in the details of the classroom, and find it hard to think 2 outside the specifics of their classrooms and students. Generalization is not always their 3 strength. 4 5 61 25 Hattie, J. (2014). Visible learning for teachers. Retrieved from http://ebookcentral.proquest.com/lib/spu/detail.action?docID=958163 Created from spu on 2017-06-12 15:16:58.  The source of ideas and the role of teachers b. Expert teachers are proficient at creating an optimal 1 2 classroom climate for learning 3 An optimal classroom climate for learning is one that generates an atmosphere of trust – 4 a climate in which it is understood that it is okay to make mistakes, because mistakes are 5 the essence of learning. For students, the process of reconceptualizing what they know so 6 that they can take on board new understandings may mean identifying errors and dis- 7 banding previous ideas. In so many classrooms, the greatest reason why students do not 8 like to expose their mistakes is because of their peers: peers can be nasty, brutal, and viral! 9 Expert teachers create classroom climates that welcome admission of errors; they achieve 10 this by developing a climate of trust between teacher and student, and between student 1 and student.The climate is one in which ‘learning is cool’, worth engaging in, and everyone 2 – teacher and students – is involved in the process of learning. It is a climate in which it 3 is okay to acknowledge that the process of learning is rarely linear, requires commitment 4 and investment of effort, and has many ups and downs in knowing, not knowing, and in 5 building confidence that we can know. It is a climate in which error is welcomed, in which 6 student questioning is high, in which engagement is the norm, and in which students can 7 gain reputations as effective learners. 8 9 20 c. Expert teachers monitor learning and provide feedback 1 This ability of expert teachers to problem-solve, to be flexible, and to improvise ways in 2 which students can master the learning intentions means that they need to be excellent 3 seekers and users of feedback information about their teaching – that is, of feedback about 4 the effect that they are having on learning. 5 A typical lesson never goes as planned. Expert teachers are skilled at monitoring the 6 current status of student understanding and the progress of learning towards the success 7 criteria, and they seek and provide feedback geared to the current understandings of the 8 students (see Chapter 7 for more on the nature of this ‘gearing’). Through selective 9 information gathering and responsiveness to students, they can anticipate when the interest 30 is waning, know who is not understanding, and develop and test hypotheses about the 1 effect of their teaching on all of their students. 2 Copyright © 2014. Taylor and Francis. All rights reserved. 3 4 d. Expert teachers believe that all students can reach the 5 success criteria 6 7 Such an expectation requires teachers to believe that intelligence is changeable rather than 8 fixed (even if there is evidence to show it may not be – see Dweck, 2006). It requires 9 teachers to have high respect for their students and to show a passion that all can indeed 40 attain success.The manner used by the teacher to treat and interact with students, to respect 1 them as learners and people, and to demonstrate care and commitment for them also needs 2 to be transparent to students. 3 This notion of passion is the essence of so much, and while we may find it difficult to 4 measure, we certainly know it when we see it: 5 61 26 Hattie, J. (2014). Visible learning for teachers. Retrieved from http://ebookcentral.proquest.com/lib/spu/detail.action?docID=958163 Created from spu on 2017-06-12 15:16:58.  Teachers: the major players in the education process 1 Passionately committed teachers are those who absolutely love what they do.They are 2 constantly searching for more effective ways to reach their children, to master the 3 content and methods of their craft.They feel a personal mission... to learning as much 4 as they can about the world, about others, about themselves – and helping others to 5 do the same. 6 (Zehm & Kotler, 1993: 118) 7 8 To be passionate about teaching is not only to express enthusiasm but also to enact it 9 in a principled, values-led, intelligent way.All effective teachers have a passion for their 10 subject, a passion for their pupils and a passionate belief that who they are and how 1 the teacher can make a difference in their pupils’ lives, both in the moment of teaching 2 and in the days, weeks, months and even years afterwards. 3 (Day, 2004: 12) 4 5 Students can see it.The Measures of Effective Teaching Project (Gates Foundation, 2010) 6 has estimated the value-added component of 3,000 teachers and at the same time asked 7 students of these teachers to complete surveys of their experiences in these classes. The 8 set of seven factors (the ‘7 Cs’) listed in Table 3.1 show dramatic differences in how students 9 see the classes of those teachers (called ‘high added-value teachers’) who have added higher- 20 than-expected achievement gains (taking into account students’ prior achievement, at the 1 75th percentile) compared with students in classes in which the gains are much lower (at 2 the 25th percentile). For example, teachers whose students claim that they ‘really try to 3 understand how students feel about things’ are more likely to be at the 75th percentile 4 than at the 25th in terms of the value-added learning that occurs in classes. 5 The picture of expert teachers, then, is one of involvement and respect for the students, 6 of a willingness to be receptive to what the students need, of teachers who demonstrate 7 a sense of responsibility in the learning process, and of teachers who are passionate about 8 ensuring that their students are learning. 9 30 1 e. Expert teachers influence surface and deep student 2 outcomes Copyright © 2014. Taylor and Francis. All rights reserved. 3 The fundamental quality of an expert teacher is the ability to have a positive influence 4 on student outcomes – and, as noted in Chapter 1, such outcomes are not confined to 5 test scores, but cover a wide range: students staying on at school and making an investment 6 in their learning; students developing surface, deep, and conceptual understandings; 7 students developing multiple learning strategies and a desire to master learning; students 8 being willing to take risks and enjoying the challenge of learning; students having respect 9 for self and others; and students developing into citizens who have challenging minds and 40 the disposition to become active, competent, and thoughtfully critical participants in our 1 complex world. For students to achieve these outcomes, teachers must set challenging goals, 2 rather than ‘do your best’ goals, and invite students to engage in these challenges and 3 commit to achieving the goals. 4 5 61 27 Hattie, J. (2014). Visible learning for teachers. Retrieved from http://ebookcentral.proquest.com/lib/spu/detail.action?docID=958163 Created from spu on 2017-06-12 15:16:58.  Copyright © 2014. Taylor and Francis. All rights reserved. TABLE 3.1 Differences in students’ views of high-value and low-value teachers on seven factors of classroom climate (the ‘7 Cs’) Created from spu on 2017-06-12 15:16:58. DIMENSIONS EXAMPLE ITEMS AT THE 25TH AT THE 75TH PERCENTILE PERCENTILE Care My teacher in this class makes me feel that s/he really cares about me 40% 73% My teacher really tries to understand how students feel about things 35% 68% Control Students in this class treat the teacher with respect 33% 79% Our class stays busy and doesn’t waste time 36% 69% Clarify My teacher has several good ways of explaining each topic that we cover in 53% 82% this class My teacher explains difficult things clearly 50% 79% Challenge In this class, we learn a lot almost every day 52% 81% In this class, we learn to correct our mistakes 56% 83% Captivate My teacher makes lessons interesting 33% 70% I like the ways in which we learn in this class 47% 81% Confer Students speak up and share their ideas about class work 40% 68% My teacher respects my ideas and suggestions 46% 75% Consolidate My teacher checks to make sure that we understand when s/he is teaching us 58% 86% The comments that I get on my work in this class help me to understand how 46% 74% Hattie, J. (2014). Visible learning for teachers. Retrieved from http://ebookcentral.proquest.com/lib/spu/detail.action?docID=958163 to improve 5 4 3 2 1 9 8 7 6 5 4 3 2 1 9 8 7 6 5 4 3 2 1 9 8 7 6 5 4 3 2 1 9 8 7 6 5 4 3 2 1 61 40 30 20 10  Teachers: the major players in the education process 1 How do expert teachers differ from experienced teachers in 2 3 these five dimensions? 4 These five dimensions of expert teachers were identified from a literature review and they 5 set the scene for a study in which we compared National Board certified teachers (NBCs) 6 (‘expert teachers’) with teachers who had applied for, but did not become, NBCs 7 (‘experienced teachers’). While we sampled more than 300 teachers, the final study 8 concentrated on those close to the ‘pass’ mark.We choose 65 middle childhood/generalists 9 or early adolescence/English language arts teachers; half scored just above and half scored 10 just below the cut-off score. For each of the five dimensions of expert teachers, we devised 1 a series of student tasks, class observation schedules, interviews with the teacher and 2 students, and surveys, and we collected artefacts of the instruction that we observed (see 3 Smith, Baker, Hattie, & Bond, 2008, for details).There were major differences in the means 4 of the two groups across all dimensions. 5 The magnitude, or importance, of the differences in these means is best demonstrated 6 by graphing the effect size of each of the dimensions (see Figure 3.1).The more accom- 7 plished teachers set tasks that had a greater degree of challenge; they were more sensitive 8 to context and they had a deeper understanding of the content being taught. More 9 importantly, there was little difference between the classrooms of expert and experienced 20 teachers in surface-level achievement outcomes, but there were major differences in the 1 proportions of surface and deep understandings: 74 per cent of the work samples of students 2 in the classes of NBCs were judged to reflect a deep level of understanding, compared 3 4 1.2 5 Essential Guiding Monitoring and Affective Influencing student 6 representations learning feedback attributes outcomes 1 7 8 0.8 9 0.6 30 1 0.4 2 Copyright © 2014. Taylor and Francis. All rights reserved. 3 0.2 4 5 0 Be tic m s ns ng m n rs sp ate on y to ves Te g le xt po g pe tom is tu y ts n ng g ev ks t ng 6 en it a hy nin in sio n es Au hes e en ke fo atic s tio vi pl ni ni rin ont im em ta ti ol ge as a ar d nc flue hall lear ar ec ob nta d t cl 7 n c le P a rs m e la on gi hi ep es r d te er le oo en ce n ac 8 i is tte ipa de p st pr t en ssr vi ito ct c al re ga Pr e i an nsit d o on 9 an En p c An e C m ee si e nc et S R d S D 40 rfa im su in tid ck 1 e ul ba e tiv M ed si 2 ha Po Fe En 3 4 Effect-size 5 61 FIGURE 3.1 Effect sizes of differences between expert and experienced teachers 29 Hattie, J. (2014). Visible learning for teachers. Retrieved from http://ebookcentral.proquest.com/lib/spu/detail.action?docID=958163 Created from spu on 2017-06-12 15:16:58.  The source of ideas and the role of teachers 80 1 70 2 60 3 Deep 4 50 5 40 6 30 7 20 8 Surface Deep Surface 10 9 0 10 Experienced Experts 1 2 FIGURE 3.2 Percentage of student work classified as surface or deep learning 3 4 with 29 per cent of the work samples of non-NBC teachers (see Figure 3.2). Students of 5 expert teachers are much more adept at deep, as well as surface, understanding, whereas 6 experienced non-experts are as adept at surface, but not deep, learning. 7 Although there have been many claims of what makes an effective teacher, too few 8 have been based on evidence from classrooms.Too often the lists have been based on simple 9 analyses of individual parts of teaching, on small numbers of teachers, and on teachers that 20 have not already been identified as expert based on rigorous and extensive assessment 1 processes. The study reported above started with an extensive review of literature and a 2 synthesis of many thousands of studies. It then led to a very detailed specification of infor- 3 mation that was gathered in classrooms over many days. This information was then 4 independently coded, using some exciting new developments in classroom observation 5 methodology.The results are clear: expert teachers do differ from experienced teachers – 6 particularly in the degree of challenge that they present to students, and, most critically, 7 in the depth to which students learn to process information. Students who are taught by 8 expert teachers exhibit an understanding of the concepts targeted in the instruction that 9 is more integrated, more coherent, and at a higher level of abstraction than the under- 30 standing achieved by students in classes taught by experienced, but not expert, teachers. 1 2 Copyright © 2014. Taylor and Francis. All rights reserved. 3 The inspired teacher 4 5 6 VISIBLE LEARNING – CHECKLIST FOR INSPIRED AND PASSIONATE TEACHING 7 8 4. This school’s professional development also aims to help teachers to seek pathways 9 towards: 40 a. solving instructional problems; 1 b. interpreting events in progress; 2 c. being sensitive to context; 3 d. monitoring learning; 4 e. testing hypotheses; 5 61 30 Hattie, J. (2014). Visible learning for teachers. Retrieved from http://ebookcentral.proquest.com/lib/spu/detail.action?docID=958163 Created from spu on 2017-06-12 15:16:58.  Teachers: the major players in the education process 1 2 f. demonstrating respect for all in the school; 3 g. showing passion for teaching and learning; and 4 h. helping students to understand complexity. 5 6 7 8 Steele (2009) has used our studies to develop a model of ‘inspired teaching’. She made 9 distinctions between the ‘unaware’,‘aware’,‘capable’, and ‘inspired’ teacher; that inspiration 10 comes both from teachers being evaluators of their own effect and from teachers taking 1 inspiration from the students – their reactions, learning, and challenges. She traces the 2 pathways for each of the dimensions: the path to solving instructional problems; the path 3 to interpreting events in progress; the path of being sensitive to context; the path to moni- 4 toring learning; the path to testing hypotheses; the path to demonstrating respect; the path 5 to showing passion for teaching and learning; and the path to helping students to under- 6 stand complexity. 7 Take, for example, showing passion for teaching and learning. Steele notes that passion 8 is not mysterious: it relates to the level of enthusiasm that the teacher shows, the extent 9 of commitment to each student, to learning, and to teaching itself, and it can be seen when 20 listening to teachers talking about student learning. 1 2 These teachers are firmly convinced that they are responsible for student learning and 3 consistently bend their efforts toward doing a better job every day. 4 (Steele, 2009: 185) 5 6 These teachers see better ways in which to teach their students; they believe that how 7 they talk about the specific topic and the ways in which they lead students to experience 8 it can make each lesson more engaging; and they believe that they are personally respon- 9 sible for student learning. Most of us recall our favourite teachers because they cared deeply 30 that we shared their passion and interest in their subject, they seemed to take extra effort 1 to make sure that we understood, they tolerated and learned from our mistakes, and they 2 celebrated when we attained the success criteria.These passionate teachers had the same Copyright © 2014. Taylor and Francis. All rights reserved. 3 time, same curriculum, same exam constraints, same physical settings, and the same class 4 sizes as other teachers, but they certainly communicated the excitement of the challenge, 5 and their commitment and caring for learning. 6 Steele notes that nearly all enter the teaching profession with a sense of idealism and 7 purpose.As we confront the realities and challenges of schools and classrooms, we can then 8 choose four roads: quit (as do about 50 per cent within the first five years); become dis- 9 connected and simply perform the role of teaching; work to become competent and seek 40 promotion out of the classroom; or learn to experience the joy of inspired teaching.The 1 difference between the inspired teacher and the capable teacher is large. I do acknowledge 2 that some commentators prefer to talk about inspired teaching (rather than teachers), arguing 3 that individual teachers can be inspired on some days, but not necessarily on all days – 4 and maybe not for all students all of the time.This is indeed the case.We know, for example, 5 that Roger Federer is not a brilliant tennis player with every shot – but this should not 61 mean that we can speak only of inspired tennis playing, and not of inspired tennis players. 31 Hattie, J. (2014). Visible learning for teachers. Retrieved from http://ebookcentral.proquest.com/lib/spu/detail.action?docID=958163 Created from spu on 2017-06-12 15:1