Abstract
Multidimensional property supplementation is a grounded theory method for analysis that conceives of concepts as multidimensional spaces of possibilities. It is applied in an iterative process comprising four steps:
Introduction
Grounded theory, a research methodology with roots in pragmatism and symbolic interactionism (Annells, 1996; Robrecht, 1995), is often associated with purely qualitative research (Charmaz, 2017, p. 2), although it was originally intended for both qualitative and quantitative purposes (Glaser, 1999, p. 842). Applying grounded theory methods correctly while maintaining openness and theoretical sensitivity presents the researcher with significant challenges. The merits and perils of
Grounded theory concepts have been likened to puzzle pieces which, when brought together, form a complete theory (Morse, 2004, p. 1392). Before the researcher can begin developing theory that “fits and works to explain a process, and is understandable to those involved in the process” (Levers, 2013, p. 1), ideas emerging from the data must be conceptualized. At least within the Straussian tradition, this entails subsuming codes under subcategories, and subcategories under categories (Corbin & Strauss, 2008, p. 159; Morse, 2004, p. 1390), thus producing a hierarchy that emphasizes “vertical” relationships—those that connect different levels of abstraction—over the more interesting “horizontal” ones of temporality and causality. Computer-assisted qualitative data analysis software (CAQDAS) tools all but enforce this practice (Bringer et al., 2006, p. 252; Hutchison et al., 2010, p. 290) which, the strengths of grounded theory notwithstanding, may be epistemologically problematic. If it could be argued that how concepts are represented not merely
This article describes
Some Weaknesses of Conceptual Hierarchies
I begin by arguing that although organizing one’s categories hierarchically makes at least some sense early in the study when vertical relationships are salient, such a structure can become an impediment to later thought. My argument targets specifically the uneasy role of the
While concepts arise through theoretical interest and thought, or even “shuffling and playing around” with words (Layder, 1998, p. 31), subcategories emerge when diversity prompts further categorization. From a pragmatist standpoint, a subcategory earns its place in the theory by capturing a difference which is There can be no difference anywhere that doesn’t make a difference elsewhere—no difference in abstract truth that doesn’t express itself in a difference in concrete fact and in conduct consequent upon that fact, imposed on somebody, somehow, somewhere and somewhen. (p. 20)
Practically significant differences are those that
More importantly, conceptual hierarchies are problematic because they obfuscate similarities and differences between subcategories. To demonstrate, I will discuss below two principally different ways that a complex concept might be structured hierarchically. It shall be made evident that each of the alternatives, which I opt to call
The concept in question, which I named the
Deep Hierarchies
Whenever some property remains unanswered by a subcategory, it becomes

Four codes related to the
First, the structure appears to imply that siblings are more alike than “cousins” on each level of the tree, but this does not necessarily hold.
Second, because each step down the hierarchy introduces conceptual assumptions, inherited properties (in our example,
Third,
Wide Hierarchies
In a

The four exemplary codes visualized in a wide hierarchy that gives equal weight to both properties
First, where deep hierarchies tend to falsely imply certain relational differences, wide hierarchies gloss over differences that do exist. Figure 2 does not, for instance, help one see that
Second, wide hierarchies scale poorly. As subcategories grow in number, keeping track of their similarities and differences will grow increasingly difficult. Ultimately, a wide hierarchy threatens to degenerate into an amorphous mess that does little to help the researcher draw conclusions about causal connections.
To conclude, although conceptual hierarchies can be useful (at least initially) for organizing one’s thoughts, they are problematic because they steer the researcher toward mistaken conclusions about the structure of represented concepts. Regardless of one’s ontological assumptions, one clearly cannot consider conceptual hierarchies to be objective mappings of reality. Instead, they should be thought of as artifacts of tradition that can, despite best intentions, obfuscate rather than clarify conceptual relationships. Tools and procedures that emphasize hierarchies make dimensionalization cumbersome, sometimes necessitating workarounds such as creating separate hierarchies for dimensions (Hutchison et al., 2010, p. 290). Although such solutions might work after a fashion, they seem counterintuitive if the goal is to visualize the internal structure of a concept. Relying on rigid tools, computer-aided or otherwise, that enforce the use of a conceptual hierarchy is therefore a questionable practice that may blind the researcher to other possibilities.
Principles of Multidimensional Property Supplementation
After these preliminaries, I will proceed to undertake the core task of this article, namely to propose a
Capturing the Concept’s Extension Through a Finite Set of Properties
To say that the extension of a concept can be The idea which the word force excites in our minds has no other function than to affect our actions, and these actions can have no reference to force otherwise than through its effects. Consequently, if we know what the effects of force are, we are acquainted with every fact which is implied in saying that force exists, and there is nothing more to know. (Peirce, 2011, p. 35)
Although qualitative researchers may balk at an example from physics, the case is not principally different in other fields. (The reader could try, at their leisure, deriving a theorem that makes more sense to them by substituting the name of their favorite concept for “force.”) The general implication of Peirce’s claim is that all we need to know about a concept can be formulated in terms of its observable effects in the world. The concept’s meaning thus consists of two parts. The first is its purpose: We think about force to explain (and successfully act upon) changes in motion. The second are the questions that must be answered with facts to enable us to make predictions: What matters in the case of force is magnitude and direction. Everything else that we might say about force can be reduced into its purpose and its properties.
In more general terms, a fully characterized concept is one that is, first, clearly enough defined to situate it firmly within the theory and making explicit what it is to explain or predict, and second, supplemented with a list of properties that help us look away from disturbing “noise” or “occasional contextual features” (Morse, 2004, p. 1390) so that we may focus on those differences that have bearing on other parts of our theory. The latter pursuit, which is my interest here, presents the researcher with a twofold challenge. First, whether a particular property is at all relevant depends on the aim of the theory, just as “[c]herry trees will be differently grouped by woodworkers, orchardists, artists, scientists and merry-makers” (Dewey, 2004, p. 88). Not much can be said in the abstract to aid such judgments. Second, the researcher must constantly navigate between
Add properties until different codes are dimensionally distinguishable.
Employ parsimony to keep the concept grounded and simple.
Address redundancy through reduction.
Add properties until different codes are dimensionally distinguishable
According to the first heuristic, no two codes that differ in practically significant ways should be left to answer similarly the questions asked by their parent, for such a state of matters would indicate that some pertinent facts remain to be theorized. (In contrast, codes that do not differ significantly may safely co-exist; occasionally, they might even serve to inspire new thoughts and hypotheses.) To address untheorized differences between codes, the researcher adds properties until codes that are intuitively different are formally separated.
Consider an example from the study on the
Properties, then, should never be added blindly; each must earn its place by
Employ parsimony to keep the concept grounded and simple
A concept’s
One threat to efficiency is
The other threat is rampant complexity. While high
Address redundancy through reduction
Despite best efforts at parsimony, a potential problem may occur in the form of
Redundancy differs from other kinds of dependency in that the gaps that it gives rise to will remain regardless of how much additional data are generated. This is because the cause is conceptual rather than empirical. To expose it, the researcher examines the properties and dimensions on a conceptual level, asking a series of questions such as the following:
Are the properties clearly defined?
Do the properties’ definitions entail their conceptual independence?
Do the dimensions provide answers to the questions asked by their properties?
Is each dimension compatible with every dimension of the concept’s other properties?
Only when all such questions can be answered in the affirmative has redundancy been ruled out. In the case that two properties are dependent in a way that puzzles the researcher, reducing them into components that can be more easily checked for synonymy might be helpful.
In principle, redundancy can be prevented by ensuring that all properties are irreducible. In practice however, strictly irreducible properties may not always be efficient, particularly if some of their dimensions are rarely seen. We are thus impelled to look for the “sweet spot” between irreducibility and efficiency. One way of conceptualizing it is in terms of
As we saw earlier, the
Explicating the Multidimensional Space of Possibilities
It is time to make explicit what I have only hinted at so far, namely that concepts can be interpreted as
The spatial metaphor
A concept that has been defined in terms of its overall purpose and theorized through carefully selected properties has two important formal second-order qualities. First, given that redundancy has been avoided, its properties will be conceptually independent; they can thus be thought of as orthogonal
According to our spatial metaphor, the extension of a concept is an

A 3-dimensional conceptual space is defined by three orthogonal axes.
A redundant yet convenient term is the
As an example, in the 4-dimensional conceptual space of the
What this brief mathematical excursion grants us is the ability to define
Inferring emergent qualities of subspaces
The dimensions that define a subspace constitute it in the sense that dimensions cannot be added, redefined, or removed without altering its meaning. But the meaning of a subspace is not exhausted by the meanings of its dimensions. On the contrary, it should be possible to add, through repeated observation, practically significant facts to the definition of subspace
For example, one of the 2-codimensional subspaces within the

A 2-dimensional projection of the
To include emergent qualities in the definition of a subspace is to
Because emergent qualities can be explained by, but not analyzed in terms of, lower-level qualities (De Sousa, 1990, p. 32), explications of subspaces will always make reference to facts beyond those represented by the constituting dimensions. As an example, the experience of being cornered is emergent from the dimensions of being
Maximizing Efficiency by Considering the Distribution of Data
I have so far argued that a parsimonious selection of independent properties can make codes dimensionally distinguishable and that such properties can be combined to produce subspaces with emergent qualities. In what follows I hope to show that whenever practically significant variability is continuously distributed rather than categorical by nature, we have reason to make these properties maximally orthogonal and minimally skewed, lest the model become wasteful. We shall see how complementing our qualitative attention to words and meanings with quantification of events can yield useful insights without committing us to the arguably “false assumption that frequency implies importance” (Bringer et al., 2006, p. 254) or otherwise transgressing methodological boundaries (Wilson & Hutchinson, 1996).
The following thought experiments presume two hypothetical properties

Two dichotomous properties that partition the data into four subspaces can be orthogonal and non-skewed (left), skewed (middle), or non-orthogonal (right).
Detecting skew as sparsity
Depending on how the researcher defines the dimensions of a property, it might come to suffer from
Three aspects of skewness are worthy of note. First, a skewed property does not imply real-world skew; rather, skew (or its absence) reflects how we conceptualize the phenomenon of interest, including our choice of dimensional cutoffs. Second, skew incurs a loss of resolution that could impede modeling of cause–effect relationships. In the diagram, our inability to distinguish between the numerous cases within subspace
Because we value conceptual resolution, avoiding skew is—all else equal—a worthy goal. It is also a mostly attainable one, except in the case of categorical or multimodal distributions.
Detecting non-orthogonality as empirical dependence
The two diagrams discussed so far show no signs of significant
There are several possible causes of non-orthogonality. As always, selection bias is one. A second, idiosyncratic coding, is particularly likely before codes have been clearly defined. A third is the presence of causal connections between properties, either directly or through confounders or mediators. While non-orthogonality may resemble redundancy, it is an empirical matter, hence our methods for revealing it are very much data-driven; a conceptual subspace might be logically consistent yet empty, indicating that the constituting combination of dimensions is perfectly possible yet unlikely to be seen for empirical (for instance, contextual) reasons. Non-orthogonality does not necessarily pose a serious problem, but is better thought of as a source of relative inefficiency, and sometimes one of lack of theoretical saturation.
The upshot of this venture into the realm of pseudo-quantification—which many qualitative researchers will no doubt find off-putting, but which I believe is in line with the original intent of grounded theory as a general methodology (Glaser, 1999, p. 842)—is this. Whenever the data are not naturally categorical, the researcher has good reason to explore signs of non-orthogonality or skew. To detect some sources of inefficiency, they need to pay at least passing attention to frequencies. While skew can in principle be identified by considering properties one by one, a multidimensional approach is clearly more sensitive. Non-orthogonality, being a multidimensional phenomenon, cannot be exposed without a multidimensional approach.
MPS as an Iterative Process
Having thus established the theoretical foundation and basic principles of MPS, I will now describe how the method is applied in practice to a would-be concept—a category—within a grounded theory study. In an iterative process, codes and properties are added, tested, and removed using Gerson’s (1991) “heterogeneity supplementation heuristics” until they account for variation within the category’s extension. The product is a multidimensional model that characterizes the category—now a concept—through relatively irreducible properties and dimensions as well as subspaces that carry emergent qualities.
The Four Steps of Supplementation
Supplementation is a process through which material for one’s theory is expanded and organized: Conceptually, it lies between coding (which names categories and specifies the properties associated with them), and theoretical sampling (which tells us what kinds of site or situation we want to look at next). Supplementation starts with an extant category, and systematically elaborates contrasting categories in order to provide the “raw material” for theoretical sampling, cross-cutting and densifying theories, and testing hypotheses. The focus of supplementation is thus on categories, not on data; on “might be” rather than “is.” (Gerson, 1991, p. 2)
Gerson distinguishes three classes of heuristics which he names
Gerson also hints at the possibility of supplementing properties, a process that he regards the “mirror image” of supplementing categories: When we use the processes of differentiation, reallocation and homogenization to supplement categories, we refer (tacitly or explicitly) to some criterion property to frame the boundaries of “similar” and “different.” When we use the same processes to supplement properties, we must use some criterion category to frame the boundaries of “similar” and “different” in the same way. (Gerson, 1991, p. 14)
I will presently describe how supplementation of properties can be used in practice to elaborate a concept multidimensionally, drawing upon examples from the study on the

The four steps of supplementation: splitting vague codes and hypothesizing contraries (
Expansion (code differentiation—property testing)
In the first step, the researcher expands the code base by making distinctions beyond those that the current model predicts. Expansion comes in two forms:
A code is
To
Besides adding codes that potentially increase the theoretical resolution of the concept, this step tests the hypothesis that the current set of properties suffice to make all necessary distinctions.
Abstraction (code reallocation—property differentiation)
To make the concept “applicable to many similar situations and contexts,” the researcher carries out “the analytic work of identifying attributes, moving beyond emic tag labels and developing careful definitions,” which Morse refers to as “decontextualization” (Morse, 2004, p. 1390). I prefer the term
Geometrization (code homogenization—property reallocation)
In this step, supplementation is driven by
Property
For a set of selected properties to be good all things considered, the implied conceptual space must be efficient. To this end, the researcher
Property reallocation is accompanied by code homogenization, which sees codes subsumed under conceptual subspaces, thus reducing their code base footprint and theoretical relevance. In return, theoretical complexity increases with the proliferation of subspaces.
Unification (code testing—property homogenization)
Working with a narrow set of abstractions incurs a risk of losing contact with both data and other parts of the theory. In this final step of the supplementation cycle, the researcher therefore employs

Geometrizing dichotomous properties
In parallel, properties are homogenized by discarding those that fail to produce subspaces significant enough to warrant the increased complexity. Given that those that remain tie in strongly with other parts of the theory (as they should), this is a process of
I defined the experience of being The GP works under the watchful eye of others, and the situation is too complex to be grasped within the allotted time. As the GP cannot simultaneously appease others and establish boundaries against the torrent of data and tasks, they are cornered, and their integrity seriously compromised. To escape, the GP must somehow convince others to cut them some slack.
This is clearly not a dictionary definition of the word “cornered,” but an explication that emerges from specific observations in a specific context. It goes well beyond the logical antecedents summarized in its first sentence and ties in—despite being abstract—with the context, embedding several factual claims that make reference to other parts of the theory: that the GP at least occasionally
In the unification step, any sparsity that indicates gaps in the concept’s empirical support is addressed. In the case of redundancy, skewness, or non-orthogonality, simplifying or modifying the model may be advisable. Barring theoretical causes, there are also procedural ones to consider, such as lack of theoretical saturation and coding idiosyncrasies. Before remedying such issues through theoretical sampling and recoding, respectively, the gaps should be reformulated as hypotheses.
Discussion
Despite being an acclaimed and widely used methodology for theory building, grounded theory continues to raise ontological, epistemological, and methodological questions. In the face of the evolution and proliferation of grounded theory methodologies (Annells, 1996; Hallberg, 2006; Melia, 1996; Rieger, 2019; Robrecht, 1995), it is fair to ask not merely what kind of methodological problems MPS can be helpful in solving, but also how compatible it is with various competing paradigms. After arguing that MPS fits well within grounded theory from the point of view of ontology, epistemology and methodology, I turn to the particular methodological strengths and weaknesses of the method. I conclude this article by outlining some possible uses of the method in the grand scheme of things.
Ontological, Epistemological, and Methodological Concerns
Whereas some methodologists consider ontology methodologically relevant (Annells, 1996, p. 379), others opt to exclude such questions from consideration because “[r]esearchers generally treat social concepts as if they are real enough to be named, investigated, and analyzed” (Carter & Little, 2007, p. 1326). I am sympathetic to the latter view because it embodies the classical pragmatist idea that “real” amounts to “being as it is regardless of what you or I may think about it” (Peirce, 2011, p. 265), which opens the door to fallibilism (Hookway, 2016) without forcing us to either assume that our beliefs somehow “represent” reality or seek refuge in relativism. From this point of view, the debate on whether knowledge is “discovered” or “created” (Levers, 2013, p. 4) appears to have little practical import.
In contrast, the view that
Methodologically, MPS does challenge some aspects of grounded theory, albeit on a rather technical level, through its questioning of traditional conceptual hierarchies. This might already mark it as suspect in the eyes of some readers, for methodology certainly provides a method with a direct mode of justification (Carter & Little, 2007, p. 1326) that MPS must do without. That said, it is questionable whether methodological justification is at all to be coveted, as it relativizes beforehand the method’s output to a particular conceptual scheme (Avis, 2003, p. 996). Arguably, claims to knowledge “cannot be reduced to a demonstration that the evidence has been generated through the application of rules and procedures derived from a coherent methodological theory” because this presumes a degree of acceptance of techniques that cannot be taken for granted outside the research tradition (Avis, 2003, p. 1003). Following this train of thought, I believe that critique of any grounded theory method should be funneled by the realization that grounded theory must, to be credible to a wider audience, be at least somewhat open to modification and extension.
Strengths and Weaknesses
This method is not intended to be applied indiscriminately to every concept across a theory. Researchers will find it useful, I believe, for elaborating complex concepts: pivotal points in addressing the main concern; choices between mutually exclusive strategies; or closely related conditions that, through their interactions, give rise to effects that are more than the sum of their parts. I would caution against using it to lump together unrelated phenomena or ones that can only be shoehorned together on the grounds that they are all “conditions” or “strategies.” Failure to name the concept accurately and evocatively is a bad sign in this respect.
One advantage of multidimensional conceptual models over hierarchical ones is that they can be made more robust, seeing as subspace definitions are literally triangulated from those of the ambient concept, constituting properties and dimensions, and subsumed codes. This is not to say that MPS is purely accommodationist (Miller & Fredericks, 1999, p. 546). Because its emergent qualities predict features of events, a multidimensional conceptual model is a falsifiable hypothesis in its own right. A conceptual model that can be falsified or corroborated also through non–grounded theory methods would seem to be a promising basis for the kind of
A crucial consideration for the purposes of this article regards the relationship between methods for concept development on one hand and theoretical sensitivity and openness on the other. It is not immediately evident that grounded theory methods in general are conducive of theoretical sensitivity, or the ability to “see relevant data” (Kelle, 2007, p. 136); it has been argued to the contrary that preoccupation with technically complex methods tends to overshadow other considerations (Thorne, 2011, p. 446), divert the researcher’s attention from the data (Kools et al., 1996, p. 315; Robrecht, 1995, p. 171), distract from actual theory building (Melia, 1996, p. 376), and be “counterproductive to the spirit of creativity” (Wilson & Hutchinson, 1996). Furthermore, method descriptions often give the false impression that the researcher is to follow a strict—or even rigid—sequence (Carter & Little, 2007, p. 1317; Layder, 1998, p. 28), whereas actual research practice may be considerably messier. Junior researchers in particular should be cautioned not to focus on the procedural aspects of the method to the detriment of insight.
One final concern regards the process of dimensionalization which, although a necessary step in the evolution of a category into a concept (Morse, 2004, p. 1390), incurs at least some risk of data forcing (Walker & Myrick, 2006, p. 552). Although the insights that “data never speak for themselves” and that interpretation “always requires moving somewhere” (Sandelowski, 2010, p. 79) may offer some consolation, one should be aware that interpretation is always relative to some frame of reference or another, be it preconceived or emerging. For this reason, it matters greatly what knowledge the researcher draws upon when choosing their direction of inquiry. The necessary practice of discarding theoretical constructs that are not “part of the world being investigated” (Cutcliffe, 2000, p. 1480) can be facilitated by postponing MPS until the concept has been located in one or several processes, at which point judging which of its properties actually make a difference elsewhere will be more straightforward.
The Use of Induction in Explicating Subspaces
Miller and Fredericks (1999) have argued that the focus of grounded theory on theory development has come at the cost of attention to “the more specific mechanisms of a logic of discovery” and that an account of how grounded theories actually explain is therefore lacking (p. 549). In what follows, I will argue that MPS adds, if not “specific rules of inductive inference,” then at least heuristics that draw upon such rules.
Somewhat confusingly, “induction” is sometimes used to denote the mode of inference that Peirce referred to as The Method of Agreement stands on the ground that whatever can be eliminated, is not connected with the phenomenon by any law. The Method of Difference has for its foundation, that whatever can not be eliminated, is connected with the phenomenon by a law. (Mill, 1884, p. 484)
In MPS, the method of agreement is used to eliminate properties that are irrelevant to an emergent quality. Given an hypothesized subspace–quality relationship, the researcher looks for
The method of difference is used to identify properties that are relevant to an emergent quality. Setting out from the highest-codimensional subspace that contains the known cases, the researcher looks for non-cases in subspaces adjacent to it on any axis. If a subspace is found that contains only non-cases, the axis (property) that joins the two subspaces together can be deemed relevant. (If a subspace contains both cases and non-cases, the emergent quality may be incongruent with how the dimensions have been defined, or else a property is missing that could make the necessary distinction.) As an example, compared with the 3-codimensional subspace from which
Multidimensional Concepts in Process
The relationship between MPS and methods for theorizing process is bilateral. We have already seen how causal hypotheses are used during the unification step to homogenize properties. The method’s
Subspace-based nodes facilitate abductive inference
Causal hypotheses may appear spontaneously in the guise of emergent qualities of subspaces that echo other parts of the theory. Such overlaps being ripe targets for theorization, a reasonable next step is to investigate the extensions of the involved subspaces—the one currently under scrutiny, and the one that it resembles—while applying abductive inference (Conlon et al., 2020, p. 948) to spell out possible horizontal (temporal or causal) relationships between them. Testing such hypotheses against theoretically sampled data can provide grounds for either rejection or corroboration (Dewey, 2004, p. 89; Heath & Cowley, 2004, p. 144). In the case of the latter, the theory can now be enriched with another inductively derived piece of generalized knowledge.
For instance, it appeared that when GPs were
Property-based nodes facilitate parsimonious causal claims
If traditional conceptual hierarchies are blunt tools for understanding vertical conceptual relationships, they fare no better with horizontal ones. Whenever one subcategory differs from another in more than one respect, causal hypotheses that draw upon their differences will easily come to overstate the relevance of merely contingent qualities. One might reasonably worry that conceptual subspaces will lead back to this quandary. They have, however, the redeeming qualities of being explicit about their constituting dimensions and—purportedly—mutually exclusive and together comprehensive with regard to conceptual possibilities. This makes it possible to rework hypotheses that reference subspaces into ones that test the respective contributions of the constituting properties. This logico-deductive approach, which resembles how MacFarlane and O’Reilly-de Brún (2012) estimated likelihoods of an ideal outcome given certain conditions, makes for more parsimonious causal claims.
As an example, although it was obvious at an early stage that the
Conclusion
A grounded theory concept can be construed as a multidimensional space of possibilities in which the concept’s properties take on the roles of orthogonal axes. I have here presented an iterative method for supplementing properties which is attentive to variation within data and facilitates theoretical separation of intuitively different events into subspaces, each of which is constituted by a unique combination of dimensions. I have argued that the method, wherever it departs from established methodology, is epistemologically well-founded because its basic principles—full characterization through properties, drawing out emergent qualities through explication, and efficiency through attention to frequencies—all adhere to the tenets of pragmatism. Using concrete examples from my research, I have demonstrated how the method fits within grounded theory methodology, and how some of its heuristics draw upon Mill’s rules of inductive inference. By virtue of being based on independent, relatively irreducible properties, multidimensional conceptual models are robust against several kinds of bias that plague conceptual hierarchies. A fully developed multidimensional concept can be easily connected to others in a process. All in all, I believe that multidimensional property supplementation is a worthy addition to the grounded theorist’s arsenal of methods for analysis and theorization.
Footnotes
Acknowledgements
The author is indebted to Lena Nordgren, Uppsala University, who helped develop and test the method, to Johan Wild for clarifying some mathematical concepts, and to researchers and doctoral students at the Centre for Research Ethics and Bioethics, Uppsala University, for helpful comments on an early draft of this article.
Declaration of Conflicting Interests
The author declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The author received funding from the Centre for Clinical Research Sörmland/Uppsala University (grants DLL-867461 and DLL-932424).
