Classification of Attachment Styles The concept of attachment and different attachment styles has a long tradition in developmental psychology. Mary Ainsworth developed a classification for three different attachment styles that she called secure, insecure-resistant or synonymously insecure-ambivalent and finally insecure-avoidant (Main, 1996). Assessment of these styles is done with the Strange-Situation-Test. Later, a fourth style called insecure-disorganized-disoriented was introduced to account for a number of children that would not have been classifiable otherwise (Main &amp; Solomon, 1990). 

A corresponding classification has also been developed for attachment styles in adults. The four styles here are called secure-autonomous, dismissing, preoccupied and unresolved-disorganized (Main, 1996). Assessment is done using the Adult Attachement Interview. 

Recently I have read a couple of papers that investigate the association between attachment styles and various forms of stress reactivity, that used the terms attachment anxiety and attachment avoidance (Selcuk et al., 2012; Ben-Naim et al., 2013; Ein-Dor et al., 2011). The authors explain what is meant by these terms. Those two attachment orientations as they are called are asses with the Experience in Close Relationships Scales (ECR, Fraley et al., 2000). I am confused as to how these terms fit into the picture of the attachment styles.

Is this another classification of attachement styles?

References:

Ben-Naim, S., Hirschberger, G., Ein-Dor, T., &amp; Mikulincer, M. (2013). An experimental study of emotion regulation during relationship conflict interactions: The moderating role of attachment orientations. Emotion, 13(3), 506–519. doi:10.1037/a0031473
Ein-Dor, T., Mikulincer, M., &amp; Shaver, P. R. (2011). Attachment insecurities and the processing of threat-related information: Studying the schemas involved in insecure people’s coping strategies. Journal of Personality and Social Psychology, 101(1), 78–93. doi:10.1037/a0022503 PDF
Fraley, R. C., Waller, N. G., &amp; Brennan, K. A. (2000). An item response theory analysis of self-report measures of adult attachment. Journal of Personality and Social Psychology, 78, 350–365. doi:10.1037/0022- 3514.78.2.350 PDF
Main, M. (1996). Introduction to the special section on attachment and psychopathology: 2. Overview of the field of attachment. Journal of consulting and clinical psychology, 64(2), 237.
Main, M., &amp; Solomon, J. (1990). Procedures for identifying infants as disorganized/disoriented during the Ainsworth Strange Situation. Attachment in the preschool years: Theory, research, and intervention, 1, 121–160.
Selcuk, E., Zayas, V., Günaydin, G., Hazan, C., &amp; Kross, E. (2012). Mental representations of attachment figures facilitate recovery following upsetting autobiographical memory recall. Journal of Personality and Social Psychology, 103(2), 362–378. doi:10.1037/a0028125 PDF
Background:

There is abundant research linking childhood attachment styles and adult attachment styles. This doesn't mean that an individual's attachment style is set in stone for life; it is a good indicator of how a child will fare as an adult.

The advent of Attachment theory:

A Brief Overview of Adult Attachment Theory and Research
R. Chris Fraley | University of Illinois


  ... Bowlby postulated that these attachment behaviors, such as crying and searching, were adaptive responses to separation from with a primary attachment figure--someone who provides support, protection, and care. Because human infants, like other mammalian infants, cannot feed or protect themselves, they are dependent upon the care and protection of "older and wiser" adults. Bowlby argued that, over the course of evolutionary history, infants who were able to maintain proximity to an attachment figure via attachment behaviors would be more likely to survive to a reproductive age. According to Bowlby, a motivational system, what he called the attachment behavioral system, was gradually "designed" by natural selection to regulate proximity to an attachment figure.


John Bowlby was the father of Attachment Theory; Mary Ainsworth tested and developed  this theory.  


  ... John Bowlby formulated the basic tenets of 
  the theory. ...
  Mary Ainsworth’s innovative 
  methodology not only made it possible to test some of Bowlby’s ideas empirically hut also 
  helped expand the theory itself and is responsible for some of the new directions it is now 
  taking. 


THE ORIGINS OF ATTACHMENT THEORY: 
JOHN BOWLBY AND MARY AINSWORTH, 
INGE BRETHERTON Developmental Psychology (1992), 28, 759-775. 

John Bowlby - Attachment Theory

It is difficult to separate more recent attachment theory from its progenitor; as this is the source from which all attachment theory has evolved.



Attachment style categorisation:

Any style of attachment, that is not a healthy or secure attachment style is classified as an insecure attachment style or an attachment disorder.   

This answer here addresses attachment disorders, in particular, ambivalent attachment disorder in detail.

Maryland's Source for 
Attachment Disorder Related Information
Note I've added bold for emphasis.


  AVOIDANT ATTACHMENT DISORDER
  
  The predominant emotion internally, in Avoidant AD {AvAD} children is sadness. However, the world sees little or none of their sadness. AvAD children believe their sadness is infinite, and should they lapse into it, they see no exit. Hence, they go to extraordinary lengths to avoid any expression of it, and usually effectively shield themselves from even recognizing their sadness. Their internal shields work so well that they often truly do not think they are sad. What AvAD children do feel is an anxious edge in quieter moments. They rarely relax, lest their sadness “creep up” on them. Their hypervigilance is more about deflecting anything that might activate their sadness rather than simply scanning for direct hostile threats. As physical / emotional closeness carries a high potential for triggering their sadness, AvAD children avoid it. Attitudinally, AvAD children are contemptuous of sadness- they define it as the “stuff of sissies”. AvAD children present themselves as omnipotent and without need for others. About half of these children lie somewhere along the spectrum of depressive disorders.
  
  ANXIOUS ATTACHMENT DISORDER
  
  The primary emotion Anxious AD {AxAD} children feel is anxiety ...
  
  DISORGANIZED ATTACHMENT DISORDER
  
  The characteristic emotion of children with Disorganized Attachment Disorder {DAD} is overwhelming and unmanageable anxiety.


A cross over of avoidance and anxiety attachment disorders:


  AMBIVALENT ATTACHMENT DISORDER  


Note: my answer gives a more comprehensive overview of Ambivalent Attachment Disorder and how it is classified as an Reactive Attachment Disorder.


  Reactive attachment disorder
  
  What is reactive attachment disorder?
  
  In reactive attachment disorder, DSM-IV considers two basic types of behavior. Representative of the hindered type of attachment disorder, is a child who “constantly refuses to initiate or respond to social activity, as it is expected of children in his age and level of development. It’s expressed in too depressed, too sensitive or highly controversial reaction, for example, a child may respond differently to the teacher: to avoid and refuse caress or to express increased vigilance (“frozen vigilance”).


Highlights of Changes from DSM-IV-TR to DSM-5


  Reactive Attachment Disorder
  The DSM-IV childhood diagnosis reactive attachment disorder had two subtypes: emotionally withdrawn/inhibited and indiscriminately social/disinhibited. In DSM-5, these subtypes are defined as 
  distinct disorders: reactive attachment disorder and disinhibited social engagement disorder. Both of 
  these disorders are the result of social neglect or other situations that limit a young child’s opportunity 
  to form selective attachments. Although sharing this etiological pathway, the two disorders differ in 
  important ways. Because of dampened positive affect, reactive attachment disorder more closely resembles internalizing disorders; it is essentially equivalent to a lack of or incompletely formed preferred 
  attachments to caregiving adults. In contrast, disinhibited social engagement disorder more closely 
  resembles ADHD; it may occur in children who do not necessarily lack attachments and may have established or even secure attachments. The two disorders differ in other important ways, including correlates, course, and response to intervention, and for these reasons are considered separate disorders




A Brief Overview of Adult Attachment Theory and Research
R. Chris Fraley | University of Illinois


  Recent research on adult attachment has revealed some interesting complexities concerning the relationships between avoidance and defense. Although some avoidant adults, often called fearfully-avoidant adults, are poorly adjusted despite their defensive nature, others, often called dismissing-avoidant adults, are able to use defensive strategies in an adaptive way. For example, in an experimental task in which adults were instructed to discuss losing their partner, Fraley and Shaver (1997) found that dismissing individuals (i.e., individuals who are high on the dimension of attachment-related avoidance but low on the dimension of attachment-related anxiety) were just as physiologically distressed (as assessed by skin conductance measures) as other individuals. When instructed to suppress their thoughts and feelings, however, dismissing individuals were able to do so effectively. That is, they could deactivate their physiological arousal to some degree and minimize the attention they paid to attachment-related thoughts. Fearfully-avoidant individuals were not as successful in suppressing their emotions.


This figure from Attachment as an Organizational Framework for Research on Close Relationships Cindy Hazan Cornell University, Phillip R. Shaver University of California, Davis; shows the basis of cause and effect underlying attachment.



Attachment anxiety and attachment avoidance.

This figure shows how this cause and effect is classified into attachment styles. Defensiveness leading to avoidance, fear leading to anxiety.



Attachment orientations

This figure taken from A Brief Overview of Adult Attachment Theory and Research gives a nice representation of how defensiveness and fear translate into attachment styles or attachment orientations. 



These diagrams also give a good representation of childhood cause and adult attachment style affect.



images courtesy of Attachment Styles
By Kendra Cherry, About.com Guide

The Experiences in Close Relationships-Revised (ECR-R) Questionnaire
Fraley, Waller, and Brennan (2000) - Iive added emphasis within this quote.


  Scoring Information: The first 18 items listed below comprise the attachment-related anxiety scale.  Items 19 – 36 comprise the attachment-related avoidance scale.  In real research, the order in which these items are presented should be randomized.  Each item is rated on a 7-point scale where 1 = strongly disagree and 7 = strongly agree.  To obtain a score for attachment-related anxiety, please average a person’s responses to items 1 – 18.  However, because items 9 and 11 are “reverse keyed” (i.e., high numbers represent low anxiety rather than high anxiety), you’ll need to reverse the answers to those questions before averaging the responses.  (If someone answers with a “6” to item 9, you’ll need to re-key it as a 2 before averaging.)  To obtain a score for attachment-related avoidance, please average a person’s responses to items 19 – 36.  Items 20, 22, 26, 27, 28, 29, 30, 31, 33, 34, 35, and 36 will need to be reverse keyed before you compute this average.