Research Policy 39 (2010) 1051–1059
`
`Contents lists available at ScienceDirect
`
`Research Policy
`
`j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / r e s p o l
`
`The technological origins of radical inventions
`Wilfred Schoenmakers a,b,c,1, Geert Duysters a,d,∗
`
`a Eindhoven University of Technology, The Netherlands
`b Maastricht University, The Netherlands
`c Hasselt University, Belgium
`d Tilburg University, The Netherlands
`
`a r t i c l e
`
`i n f o
`
`a b s t r a c t
`
`Article history:
`Received 17 April 2007
`Received in revised form 24 March 2010
`Accepted 26 May 2010
`Available online 1 July 2010
`
`Keywords:
`Radical inventions
`Patents
`Alliances
`Open innovation
`Organizational learning
`
`1. Introduction
`
`This paper aims to trace down the origins of radical inventions. In spite of many theoretical discussions on
`the effect of radical inventions, the specific nature of radical inventions has received much less attention
`in the theoretical and empirical literature. We try to fill that void by an empirical investigation into the
`specific origins of radical inventions. We explore this issue by a close examination of 157 individual
`patents, which are selected from a pool of more than 300,000 patents. In contrast to the conventional
`wisdom that radical inventions are based less on existing knowledge, we find that they are to a higher
`degree based on existing knowledge than non-radical inventions. A further result that follows from our
`analysis is that radical inventions are induced by the recombination over more knowledge domains. The
`combination of knowledge from domains that might usually not be connected seems to deliver more
`radical inventions.
`
`© 2010 Elsevier B.V. All rights reserved.
`
`Inventions come in many different forms ranging from incre-
`mental or run-of-the-mill inventions, to radical or breakthrough
`inventions. Most inventions can be characterized as incremental
`inventions. Incremental inventions consist of minor improvements
`or plain adjustments to existing products or technology. Their
`individual impact on the technological system is usually limited.
`Radical inventions on the other hand are generally considered as
`being a risky departure away from existing practice (Hage, 1980).
`Radical inventions exhibit key characteristics that are inherently
`different from existing products or technologies. They often lie at
`the hart of changes in technological paradigms (Nelson and Winter,
`1982), thereby creating new technological systems and sometimes
`even new industries. Although incremental inventions might be
`a principal source of measured productivity growth, without the
`original radical invention they would not have been possible. Rad-
`ical inventions are thus considered to be a crucial basis for a
`sequence of subsequent developments around this original inven-
`tion (Mokyr, 1990).
`In spite of many theoretical discussions on the effect of radical
`inventions (e.g. Ahuja and Lampert, 2001; Rosenkopf and Nerkar,
`2001; Dahlin and Behrens, 2005; Tellis et al., 2009), the specific
`
`∗ Corresponding author at: Eindhoven University of Technology, The Netherlands.
`E-mail addresses: W.W.M.E.Schoenmakers@tue.nl (W. Schoenmakers),
`G.M.Duysters@tue.nl (G. Duysters).
`1 Tel.: +31 402472170.
`
`0048-7333/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
`doi:10.1016/j.respol.2010.05.013
`
`nature of radical inventions has so far remained relatively unclear.
`In fact, large-scale empirical studies into the technological ori-
`gin of radical inventions are sparse and almost non-existing. Most
`previous studies on radical inventions have focused on the Schum-
`peterian size based discussion about the role of small and large
`firms in the creation of radical inventions and innovations. The
`empirical results of these studies however remain mixed (Scherer,
`1991). Others have focused on organizational aspects influenc-
`ing the development of radical inventions (for an overview see
`Chandy and Tellis, 1998). In order to advance theory and practice
`we will argue that it is critical to understand the specific tech-
`nological characteristics that influence the development of radical
`inventions. In contrast to many existing studies we are primarily
`interested in the technological origins of radical inventions rather
`than the market success. We therefore depart from the commonly
`used innovation aspects and focus instead on the invention itself.
`In particular we would like to contribute to the classic discus-
`sion of whether radical inventions are based on completely new
`knowledge (Poel, 2003) or can be seen as an artefact resulting
`from the recombination of existing knowledge (Schumpeter, 1939;
`Fleming, 2001; Nerkar, 2003). A better understanding of the origins
`of radical inventions might guide organizations in their decisions
`to either focus on internal development for the creation of new
`knowledge or to resort to “open innovation” in their search for
`“neue combinationen” (Schumpeter, 1939). From a societal aspect,
`more knowledge about the origins of radical inventions is impor-
`tant because of the potential impact of this particular kind of
`inventions in creating new technological systems or even new
`industries.
`
`1051
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`Lockwood Exhibit 2003
`GSI v. Lockwood
`IPR2014-00025
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`2. Theoretical background and hypotheses
`
`The importance of radical inventions has been demonstrated
`in many different publications. (e.g. Ahuja and Lampert, 2001;
`Rosenkopf and Nerkar, 2001; Dahlin and Behrens, 2005). There
`is a clear consensus among scholars and practitioners that radi-
`cal inventions are driving forces of technological, industrial and
`societal change. Whereas the impact of these inventions on the
`global economy has been described extensively in the literature,
`much less is known about the particular nature or origins of radi-
`cal inventions. Apart from a few notable exceptions (e.g. Ahuja and
`Lampert, 2001) the technical content of a radical invention has not
`been studied extensively. Instead, existing studies focused on the
`issue of innovation rather than invention. In a seminal article, Ahuja
`and Lampert (2001, p. 523) define radical or breakthrough inven-
`tions as “those foundational inventions that serve as the basis for
`many subsequent technical developments”. In this definition Ahuja
`and Lampert address the technical content of an invention. They
`do not consider the inventions that are radical from a user or mar-
`ket perspective, but instead they focus only on the technological
`importance of inventions. Second, they define radical inventions
`as those inventions that serve as a source for many subsequent
`inventions. Their premise is thus that radical inventions are those
`inventions whose technical content will be used by many succes-
`sive inventions (see also Trajtenberg, 1990a; Trajtenberg, 1990b).
`Dahlin and Behrens (2005), on the other hand, consider technolo-
`gies to be radical when they are: (1) novel, (2) unique, and (3)
`have an impact on future technology. The term novel needs some
`clarification. In this definition they include radical inventions that
`are constructed of already existing, but beforehand-unconnected
`knowledge (Hargadon, 2003). In order to be labelled as a radical
`invention, new knowledge, or the recombination of already exist-
`ing knowledge must be unique. The last point in the definition of
`Dahlin and Behrens (2005), concerning the impact of radical inven-
`tions on future technology, is in line with the definition given by
`Ahuja and Lampert (2001). They also consider radical inventions as
`those inventions with a relatively major impact on future inven-
`tions. An invention is thus considered radical if relatively many
`subsequent inventions build on it. Therefore, impact on subsequent
`inventions can be seen as a proxy for radicalness. In a similar vein
`we consider all inventions that serve as an important antecedent
`for later inventions as radical invention. We thus use the impact
`of inventions on subsequent inventions as an approximation for
`the radicalness of an invention. In this study we will discuss their
`particular nature in retrospect. Hereby we will focus our attention
`solely on technological inventions.
`The discovery of radical inventions is sometimes mystified and
`glorified. Many people still have an idealised picture of the lone
`inventor in a laboratory stocked away from the outside world for
`many years waiting for his/her moment of glory. The lone inventor
`is rather the exception than the rule (Hargadon, 2003). Although
`the lone inventor still exists (Dahlin et al., 2004) mostly a team
`of experts on different fields joins forces in order to develop radi-
`cal inventions. Another myth is that radical inventions are always
`based on completely new knowledge (Poel, 2003). In fact, the
`recombination of existing knowledge is proposed by many schol-
`ars to be the ultimate source of novelty (Fleming, 2001; Nerkar,
`2003). Even Schumpeter (1939) in the late 1930s considered inven-
`tion as new combinations or “neue combinationen” (Schumpeter,
`1934, pp. 65–66). Nelson and Winter (1982, p. 130) assert “. . .
`that invention in the economic system . . . consists to a substan-
`tial extent of a recombination of conceptual and physical materials
`that were previously in existence”. Even a simple rearrangement of
`components that are already in use, can, according to Henderson
`and Clark (1990), be a main cause of destabilisation in key indus-
`tries. In a similar vein Hargadon and Sutton (1997) have described
`
`how firms create novelty by being a technology broker. Fleming
`states that “. . . an invention can be defined as either a new com-
`bination of components or a new relationship between previously
`combined components” (Fleming, 2001). According to Hargadon
`(2003) radical inventions are only rarely based on completely new
`knowledge. Most of the time radical inventions come from a recom-
`bination of already existing knowledge. “When . . . connections are
`made, existing ideas often appear new and creative” (Hargadon and
`Sutton, 1997, p. 716). Particularly important in this respect is the
`recombination of beforehand-unconnected knowledge or uncon-
`nected knowledge domains (Hargadon, 2003).
`However, large-scale empirical evidence is still unavailable and
`a number of scholars would contend that a radical invention is likely
`to be based on truly novel knowledge and thus goes beyond simple
`recombination, irrespective of examples of inventions based on the
`recombination of existing knowledge or the discovery of a new con-
`text for already existing knowledge (Poel, 2003). We believe that
`radical inventions originate from two basic sources, the recombi-
`nation of existing knowledge as well as from the creation of truly
`novel knowledge. Therefore we hypothesize that radical inventions
`are generally based on existing knowledge.
`
`H1. Radical inventions are equally based on existing knowledge,
`as non-radical inventions.
`
`As discussed above, radical inventions are for a substantial
`part dependent on already existing but beforehand-unconnected
`knowledge. This existing knowledge comes about in two different
`forms, mature knowledge, and emergent knowledge. The recombi-
`nation of existing knowledge can therefore be based on either “old”
`or mature knowledge, or on “new” or emerging knowledge, or on
`a combination of both. In the literature there is a debate going on
`about the importance of mature and emergent technologies (Ahuja
`and Lampert, 2001; Nerkar, 2003). Emerging technologies are tech-
`nologies that have come to the market only recently, and that
`are considered to be cutting edge technology (Ahuja and Lampert,
`2001). Emerging technologies offer many opportunities for devel-
`oping new recombinant technologies. Emerging technologies can
`offer firms valuable new components that facilitate the devel-
`opment of radical inventions (Ahuja and Lampert, 2001). Firms,
`however often lack the deep understanding of emerging technolo-
`gies, which is needed to develop radical inventions. Firms that
`tend to rely on emerging technologies often have difficulties in
`understanding the real properties of this knowledge and there-
`fore can only contribute in a limited way in terms of developing
`future technologies (Nerkar, 2003). In contrast, mature technolo-
`gies are well comprehended and have been tested and used in
`many different settings. They “are usually well understood and
`offer greater reliability relative to more recently developed and
`less tested” technologies (Ahuja and Lampert, 2001, p. 527). Firms,
`and especially incumbent firms, will prefer mature technologies
`to nascent technologies. They are more familiar with them, and
`they are more aware of the specific properties of the technologies.
`The outcomes of emerging technologies are much more uncertain.
`This is also related to the concept of absorptive capacity as intro-
`duced by Cohen and Levinthal (1990). Firms invest in R&D and as a
`result build up absorptive capacity in their organization. Absorptive
`capacity is generally path dependent and in line with a firms’ cur-
`rent research. With emergent technologies, firms will thus, overall,
`face more difficulties in absorbing them. Firms that focus on the
`use of existing technologies may benefit from their high degree of
`absorptive capacity and are therefore often able to speed up the
`innovation process.
`Firms that concentrate on emerging technologies might suf-
`fer from experimentation costs and limited output. Dealing with
`emerging technologies is often problematic. It often takes a long
`time to discover the specific characteristics of the technology and
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`many of the emerging technologies turn out to be less viable then
`previously expected. Emerging techniques could also ask for dif-
`ferent routines, which would require existing employees to change
`their current routines; routines the employees have been familiar
`with for a long time, and who are subsequently difficult to change
`(Nelson and Winter, 1982). Emerging technologies thus, on the one
`hand pose many opportunities but on the other hand also pose
`many considerable difficulties that are not easy to cope with in
`this particular stage of development. In spite of the difficulties that
`emerging technologies present, we still expect that firms will need
`emergent knowledge to produce radical inventions. Mature tech-
`nologies are important, but there is an increasing consensus that
`emergent technologies are also very important, especially for rad-
`ical inventions. We would thus expect that radical inventions are,
`as compared to non-radical inventions, to a higher degree based on
`emergent technologies.
`Our second hypothesis is therefore:
`
`H2. Radical inventions are to a higher extent based on emergent
`technologies, as compared to non-radical inventions.
`
`In spite of the expected positive relationship between emergent
`technologies and radical inventions, relying too much on emergent
`technologies will lead to new knowledge that only has a lim-
`ited impact on future technologies, while depending too much on
`mature knowledge might not lead to very innovative ideas or might
`lead to incremental inventions only (Nerkar, 2003). Mature tech-
`nologies provide very little opportunities for radical inventions.
`On the other hand, mature technologies are not always publicly
`known and are sometimes not used to their full potential at the
`time of their development and might consequently be forgotten,
`not because they are not useful, but because at the time of their
`development they could not be employed. This, for example, has
`to do with the co-evolution of complementary knowledge, institu-
`tions, or standards that are necessary in order to use the new piece
`of knowledge (Nerkar, 2003). In many cases mature technologies
`are complemented by other technologies in order to facilitate the
`rapid development of new inventions. Mature technology is gen-
`erally well understood as compared to emerging technologies. The
`combination of mature and emergent technologies could therefore
`potentially be very beneficial because it allows new combination of
`different streams of knowledge that might facilitate the develop-
`ment of radical inventions. Furthermore mature knowledge might
`finally be used to its full potential once complementary technolo-
`gies become available. We therefore expect that radical inventions
`are much more based on a combination of mature and emergent
`technologies.
`Our third hypothesis is therefore:
`
`H3. Radical inventions are to a higher degree based on a com-
`bination of mature and emergent technologies than non-radical
`inventions.
`
`Despite the market advantages of combining technologies, firms
`also tend to search for new knowledge locally, i.e., within the
`current field of expertise of the firm (Stuart and Podolny, 1996),
`and within the same geographical confinement (Verspagen and
`Schoenmakers, 2004). Firms often treasure the convenience of
`technological and geographic proximity in their search process.
`They tend to stick to their current structures and routines. As a
`result, companies often suffer from bounded rationality and are
`therefore often dealing with only a limited subset of the total
`knowledge domain. According to Granstrand et al. (1997, p. 13)
`the technological competencies of large firms depend heavily on
`their past and are fairly stable. Knowledge is thus “imperfectly
`shared over time and across people, organizations, and industries”
`(Hargadon and Sutton, 1997, p. 716). This could potentially lead to
`the development of “core-rigidities” (Leonard-Barton, 1995) and
`
`to the emergence of “competency traps” (Levitt and March, 1988).
`These traps could well prevent the firm from developing radical
`inventions. Research by Sorensen and Stuart (2000), for instance,
`suggests that firms that rely more on their previously developed
`knowledge deliver more inventions, but these inventions are less
`relevant.
`Research by Granstrand et al. (1997), Patel and Pavitt (1997)
`and Brusoni et al. (2001) suggests that a firm’s technological port-
`folio typically is larger than its product portfolio. The reason for this
`is that firms need to search for interesting technologies emerging
`outside their core technological domain. This broad perspective on
`technological competencies is thus necessary for firms in order to
`explore and exploit new technological opportunities (Granstrand
`et al., 1997). Firms that aim to innovate often need a broader knowl-
`edge base in order to do so. This also implies that radical inventions
`are based on various knowledge domains. Radical inventions not
`only serve as the basis for many successive inventions (Trajtenberg,
`1990b), but can also be expected to build on a larger knowledge
`base (Rosenkopf and Nerkar, 2001). Differences in terms of the
`number of knowledge components that make up an invention will
`appear in all kinds of incremental as well as in radical inventions. A
`larger knowledge base on the other hand also points at the diversity
`in the number of different knowledge bases or knowledge domains
`that constitute an invention. Radical inventions can be expected to
`draw from a broader knowledge pool than non-radical inventions.
`If we assume that radical inventions are based on new combina-
`tions of already existing knowledge, as discussed before, then this
`combined knowledge legacy can be expected to come from various,
`different knowledge domains. In today’s world it is very unlikely
`that radical inventions are based on just one single knowledge
`domain.
`Our fourth hypothesis is therefore:
`
`H4. Radical inventions are based on a relatively large number of
`knowledge domains, compared to non-radical inventions.
`
`3. Data
`
`For our research we will be looking at so-called radical inven-
`tions. Inventions are associated with the development of a new
`idea, whereas innovations refer to the commercialization of this
`idea (Schumpeter, 1934; Hitt et al., 1993; Ahuja and Lampert, 2001).
`As discussed we will not be looking at the commercialization of an
`idea in this paper, but rather at the act of creating an idea. We are
`particularly interested in how an invention can be a catalyst for
`the development of subsequent inventions. We especially want to
`focus on those inventions that can be considered radical or break-
`through. Therefore we focus our attention to those inventions that
`serve as a basis for many successive inventions.
`Patent data is the single most dominant indicator in invention
`studies. For a patent to be granted it must be novel, non-trivial,
`and useful. If a patent meets these requirements, a legal title will
`be created containing information on for instance the name of the
`inventing firm and also on the technological antecedents of the
`knowledge, the patent citations. In the European Patent Office (EPO)
`system, the patent applicant can include citations to prior patents
`(and prior technological and scientific literature), but ultimately it
`is the patent examiner from the patent office who determines what
`citations will be included in a patent (Michel and Bettels, 2001).
`Patent citations reveal the so-called “prior art” of the newly devel-
`oped patent. Citations to other patents, the so-called backward
`citations, indicate on what preceding knowledge the new patent
`is based. They provide a kind of patent family tree. The citations
`from other patents to a patent, the so-called forward citations, on
`the other hand are an indication for the importance of the patent.
`Patents with higher numbers of forward citations are considered to
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`also have a higher economic value for the firm possessing the patent
`(Trajtenberg, 1990a; Harhoff et al., 1999). Forward citations are also
`considered to be a good indication for the technological importance
`of an invention (Dahlin and Behrens, 2005). Firms with more highly
`cited patents also enjoy economic benefits (Trajtenberg, 1990a) and
`have on average higher stock market values (Hall et al., 2001).
`In the research of Harhoff et al. (1999) it was shown that firms
`are willing to pay the renewal fees only for important inventions,
`which leads firms to have only the maximum patent protection
`for important inventions, leaving less important inventions with a
`shorter patent protection period. This behavior leads to more cita-
`tions for important inventions since they have a longer patent-life,
`but on the other hand they also find that, of the patents with a full-
`term patent protection period, the citation frequency rises with the
`economic value of the invention, as reported by the firm.
`In line with the research of Ahuja and Lampert (2001) we will
`use forward patent citation counts to identify radical inventions,
`and will consider inventions radical if they serve in a more than
`average way as the basis for subsequent inventions. Patent citation
`counts are considered to be good estimators of the technological
`importance of inventions (Narin et al., 1987; Albert et al., 1991).
`Highly cited patents are also considered an important indicator for
`radical inventions (Trajtenberg, 1990a). We will base our definition
`of radical inventions on Ahuja and Lampert’s (2001) definition, as
`described above. Dahlin and Behrens’ (2005) definition is also in
`line with the definition given by Ahuja and Lampert. Dahlin and
`Behrens (2005) define inventions as radical if they are (1) novel, (2)
`unique, and (3) have an impact on future inventions. Since patents
`are supposed to be novel and non-trivial, covering more or less
`prerequisites 1 and 2, their definition is the same, in the case of
`patents, as the one by Ahuja and Lampert (2001). So we are look-
`ing for patents with a more than average influence on subsequent
`patents. We will be using the EPO (European Patent Office) database
`of patent data as our primary data source.
`Patent citations are often referred to as “noisy indicators” of
`knowledge flows (Jaffe et al., 1998, 2000). The reason being that
`large parts of patent citations may not be related to a particular
`knowledge flow due to the fact that patent citations are included
`not only by the inventor, but as well by the patent attorney of the
`firm and the patent examiner in the patent office. Recent research
`has concentrated on the distinction between inventor citations and
`non-inventor citations (Alcacer and Gittelman, 2006; Criscuolo and
`Verspagen, 2008). Where Criscuolo and Verspagen propose only to
`consider inventor citations as knowledge flows, Alcacer and Gittel-
`man conclude that the bias introduced by the examiner citations
`is not necessarily bad, since both inventor citations and examiner
`citations might track each other closely. Also, in the EPO system,
`inventors might make use of knowledge without being aware of
`the existence of a patent for this piece of knowledge, or without
`even bothering to include a citation. Inventors also might sim-
`ply forget to include a citation, or even deliberately not include
`a citation for strategic reasons. In all these cases a knowledge flow
`exists but is not visible in the inventor citations. However un-logical
`these examples might sound in the US Patent and Trademark Office
`(USPTO) system, in the EPO system they are not. Especially in the
`EPO system, which we are using for our research, it is the patent
`examiner of the patent office who is ultimately responsible for
`including all the patent citations that are necessary, and not the
`inventor. Together this might also be the reason why Criscuolo and
`Verspagen’s (2008) finding that inventor citations and examiner
`citations in EPO do not track each other differs from the findings
`of Alcacer and Gittelman (2006) for USPTO. Also in terms of legal
`reasons inventor and non-inventor citations in USPTO will track
`each other more closely than these citations will do in EPO. Fur-
`thermore, due to the different requirements of EPO and USPTO,
`also the examiner included citations in EPO can be expected to be
`
`much more related to the prior art of the invention, as would fol-
`low from the examples given here before. So in contrast to Criscuolo
`and Verspagen (2008) we do not feel that in the EPO system it is
`only the inventor citations that should be considered when looking
`for knowledge flows. Although we agree with them that, especially
`when compared to USPTO, inventor citations in EPO very probably
`do indicate a knowledge flow, in EPO also non-inventor citations
`might very well be an indication of a knowledge flow. In other
`words, we cannot exclude the possibility that a non-inventor cita-
`tion indicates a knowledge flow in the EPO system. In USPTO there
`is furthermore the problem that applicants include even remotely
`related citations just to make sure that they do not run any risk
`of compiling an incomplete list of citations (Michel and Bettels,
`2001) which practice introduces “noise” already at the inventor
`citations. EPO citations can thus be considered less “noisy”, for the
`included citations are less influenced by the fear of legal reper-
`cussions (Criscuolo and Verspagen, 2008). Duguet and Macgarvie
`(2005) finally conclude that patent citation counts are relevant for
`knowledge flows, although not for all the channels though which
`firms obtain knowledge. Admitting thus that patent citation are
`a “noisy” indicator of knowledge flows we still feel confident that
`they can be used as an indicator of knowledge flows for our purpose,
`especially since we are using the less “noisy” EPO data. Further,
`even though we collect our data on the individual patent level, for
`our analysis we make use of aggregated scores for the two groups
`of patents that we consider, and as an aggregated variable patent
`citations are considered to be useful regardless of their individual
`“noisiness” (Jaffe et al., 2000).
`While using the EPO database we might encounter two inherent
`problems. The first has to do with the difference of the num-
`ber of patents applied per measuring year. Previous research (see
`Schoenmakers, 2005) has shown that in EPO data the number of
`patents applied increases from the start of EPO in 1978 till about
`1989. From thereon the number of patents applied stays more or
`less stable. We cannot use the period where the number of patents
`applied is not stable, since patents who get applied in a period
`where there were relatively few other patents applied will have,
`only because of this reason, less chance of receiving forward cita-
`tions compared to a patent that is applied in a period with more
`other patents applied. This is the case, simply because there are
`more patents that potentially could cite the specific patent. This
`is especially true since we know that the bulk of forward citations
`are received within the first four to five years after the initial patent
`application (Schoenmakers, 2005). Since we do not want the num-
`ber of forward citations per patent to be dependent on the number
`of patents applied in a given year but only on the technological
`importance of the patent, we need to confine our research to that
`period where the number of patents applied in EPO is more or less
`equal, which is the period from 1989 till 1998.2
`A second problem might occur when we compare patents from
`different periods with each other. Older patents will have a higher
`chance of receiving forward citations, simply because the period
`over which the citations are counted is longer compared to younger
`patents. In order to tackle this problem we counted for every patent
`the number of forward citations it received up till five years after
`
`2 Normalization of the measuring years would also have been possible that would
`have been the other option to correct for the differences in numbers of patent per
`year. This would have made it possible to use a longer time period. We choose
`however to correct this problem by only considering the years with more or less
`equal numbers of patents. An important reason for our choice was that since the time
`period that we consider is relatively short we can also expect that other variables,
`which we cannot control via normalization or otherwise, are more or less constant
`over the measuring period. We therefore felt that using our approach was the most
`appropriate choice in this specific context.
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`its initial application date (usually the filling date of the patent).3
`This means that for patents applied for in January 1989, we counted
`the citations up to and including those applied in January 1994, for
`patents applied in February 1989 we counted the citations until
`February 1994, etc. Since we can only use the patents between
`1989 till 1998, the last year we used patents from is 1993. A similar
`approach is used by earlier research (Schoenmakers, 2005). Even-
`tually we got a list of 300,119 patents that were applied for in the
`period from January 1989 till December 1993 with their individual
`numbers of forward citations.
`Since we expect, in line with Ahuja and Lampert (2001) and
`Dahlin and Behrens (2005), that radical inventions are a rather rare
`phenomenon, we selected only the most highly cited patents as our
`group of radical patents. The highest cited radical patent received
`54 citations and the least cited 20 citations. We put our cut-off value
`at 20 citations based on the before mentioned expectation that truly
`radical inventions will rather be an uncommon occurrence, and
`we observed that many patents have 19 or less citations, whereas
`only very few have more than 20 citations. Although this cut-off
`value of 20 might still seem rather arbitrary, one has to consider the
`severity of the mistake that we might make. We could either forget
`to include some of the truly radical inventions or we might include
`some non-radical inventions in our radical group. In both cases this
`could only weaken our results, meaning that if we find a difference
`between radical and non-radical inventions, our results could even
`have been stronger if we had used a different cut-off point. We
`therefore feel confident that our cut-off point is not leading us to
`make a major mistake. Since the mistake of excluding some of the
`radical inventions from the radical group would altogether lead to
`the highest chance of making the smallest mistake we choose to
`be rather conservative with marking inventions as radical. We are
`therefore convinced that the construction of our group of radical
`inventions is suitable for our research questions. We ended up with
`a group of 96 radical patents.
`For the construction of the non-radical inventions we randomly
`selected 96 patents from the group of patents with less than 20 for-
`ward citations. For both groups we collected the necessary variables
`using, besides EPO, Worldscope. W