Design and Procedure

A within subjects post-test design with no control group was used. All subjects were given background information about analogies prior to analogy generation. This information included a definition of an analogy, its components, and examples of other analogies. Subjects were then given different paragraphs of scientific content and asked to individually generate analogies for each. There was no collaboration in the generation of analogies.

Selection of Concepts for Analogy Generation.

Science content has been organized in a number of ways, most frequently by discipline. Because of the range of concepts within each discipline, the researchers felt that a more specific categorization was needed to operationalize the types of concepts for which analogies would be generated. Categorizing science content into whether it involved structure or process seemed to be one possible way to study concrete and abstract concepts, without the constraint of scientific discipline. This dichotomy was similar to Lawson’s (1993) grouping of “descriptive” and “theoretical” concepts (p. 1213) and to a previous categorization of analogies. Thiele (1994) categorized analogies in another way, as structural or functional. Structural analogies were identified as those where the analog and target were structurally similar whereas functional analogies were defined as those where the analog reflected the behavior of the target (Thiele, 1994). Although the researchers in the current study were examining the effect of content on the quality of generated analogies, it appeared as if process or structure concepts might also affect the type of analogy generated. Therefore, the researchers decided to use a structure-process dichotomy for the current study.

Structure was defined as content focusing on static, definable features such as the layers of the Earth, parts of a plant, cloud types, or the arrangement of atoms in a molecule. Even when these features were not observable, they appeared to have observable counterparts, similar to Lawson’s (1993) “perceptible exemplars” (p. 1213). It was hypothesized that the observable aspects would make these concepts more concrete to learners. Process content was defined as a dynamic condition or a series of actions ending in a specific result, such as convection in the mantle, photosynthesis, or the water cycle. Many unobservable elements seemed to make these concepts more abstract and comparable to Lawson’s (1993) “theoretical” (p. 1213) categorization. For example, when discussing the convection currents in the mantle, it is not possible to observe the slow heating of rock, the melting of rock, or the movement of rock like a fluid.

Multiple process and structure concepts were generated for possible analogy generation and then organized according to scientific discipline. Two concepts found in elementary science texts, one in the domain of physical science and the other in earth science, were initially selected for analogy generation. The Earth’s layered interior was selected for the structure concept while heat conduction in solids was chosen for the process concept. Heat conduction in solids was also selected because of the role of particulate matter; a content area where misconceptions have previously been identified (American Association of Physics Teachers, 1996; DeVos & Verdonk, 1987; Gabel, Samuel, & Hunn, 1987). It was hypothesized that generated analogies and accompanying information about the similarities and differences between analog and target would reveal possible misconceptions.

The researchers decided to begin with one structure and one process concept in order to determine whether this dichotomy was specific enough to capture quantitative and qualitative differences in analogies generated for concrete and abstract concepts across scientific disciplines. Starting with the generation of two analogies would also enable an examination of possible assessment tools to determine whether quantifiable differences between analogies could be captured.

Evaluating Generated Analogies. A Validity Scale (Zook & Myer, 1994) was used to obtain an analogy quality score. Key aspects of each concept were determined prior to scoring. For example, for the Earth’s layered interior, the following were determined to be main points: layered interior (at least 3 layers evident), layers different thickness’ (ideally, outermost thinnest), layers composed of different materials (ideally, outer layer brittle, rock-like), and each successive layer surrounded by others. To receive the maximum number of points (5), all key aspects had to be evident in the analogy. Table 2 illustrates the scoring of one analogy using the previously identified key aspects.

Table 2

Critical aspects used to evaluate heat conduction analogies included both general and specific components. There were key aspects related to heat conduction such as evidence of energy application and the initiation of particle movement. There were also key aspects related to the differences between a good and a poor conductor such as particles tightly packed in a rigid structure compared to particles structured in a random manner with more space between them.

Explanations about the analogies written by subjects were coded according to whether similarities and differences between source and target concepts were provided and whether the information was scientifically correct. Analogy limitations were additionally coded according to whether they were superficial, an obvious observation dealing with surface level similarities and differences. For example, one explanation listed as superficial involved the difference between a layered candy (“Gobstopper”) and the Earth’s layered interior. In this case, the subject wrote, “One is much smaller than the other, and one is food.”

It was more difficult for subjects to generate analogies for the process than the structure concept. Over one-fourth (27%) did not generate an analogy for heat conduction while only 5% failed to do so for the Earth’s layered interior. When the absence of analogies was further examined, it revealed that 43% of the “no analogy” responses for heat conduction were examples of good or poor conductors rather than analogies while 14% were ideas for activities or demonstrations. One respondent noted, “You could demonstrate this very easily by heating the metal and showing how hot it gets and same with wood – just keep it from burning. I don’t think you need an analogy.” None of the “no analogy” responses for the Earth’s interior were examples or activities.

The majority of written explanations about the similarities and differences between source and target concepts were coded as superficial. Examples of explanations coded in this way included, “The Earth’s interior is not made up of food,” “You can eat a sandwich, you can’t eat the Earth,” and “Particles in metals are smaller than cars.”

Analog domains for analogies generated for the Earth’s interior structure were primarily food. Source domains for heat conduction analogies included both indoor and outdoor games, game equipment, experiences on highways, and comparisons between cities and towns. Tables 3 and 4 provide a representative sample of analogies generated for each concept.

Table 3

Table 4

Table 5 illustrates how one of the representative analogies for heat conduction was scored.

Table 5

Scored Analogy: A good conductor is like a ball pit with a lot of balls while a poor conductor is like an empty ball pit.

Analogy Validity

Analogies generated for the Earth’s layered interior (structure) and heat conduction (process) were evaluated using the adapted Validity Scale (Zook & Myer, 1994). Subjects generated significantly more valid analogies for structure than process content, Z = -6.15, p = .00. The mean validity score for generated analogies was higher for the Earth’s interior than heat conduction, 3.53 and 1.26, respectively. Only one pair of conduction analogies received the maximum score. Table 6 provides descriptive statistics for each general content area.

Table 6

Previousresearch found a dissociation between structure and process in theunderstanding of tectonic processes (Nottis, 1996). In this study,there was some dissociation found between structure and process inthe analogies generated for heat conduction. Although the topic ofheat conduction was labeled a “process” concept, keyaspects identified for scoring the validity of these analogiesincluded both structural and process components. Two structuralaspects dealt with solids being composed of a group of smallparticles and the compactness of particles varying, depending uponwhether something was designated a good or a poor conductor.Generated analogies were most likely to include these structuralaspects, even though they were unobservable, and least likely toinclude process aspects, such as the application of energy (heat) andits transference from particle to particle. They could be categorizedmore as structural rather than functional analogies (Thiele, 1994).Finally, there was a significant, weak positive correlation betweenthe structure and process scores: r_s = .26, p< .05.

Inter-RaterReliability

Inaddition to the researchers, an individual with a background ingeoscience also rated each of the generated analogies using theValidity Scale (Zook & Myer, 1994). Inter-rater reliability wasthen computed. There was a significant, strong positive correlationbetween the researchers and the outside rater’s scores forstructure content, r = .87, p = .00. However, this wasnot maintained for scoring of process content. In this case, scoreswere only moderately, positively correlated, r = .49, p< .05. An examination of scoring differences revealed that theoutside rater tended to give lower scores than the researchers. Aftera discussion of more explicit “possible violation” and“violation” criteria, the outside rater blindly rated thegenerated analogies after a month time lapse. Scoring of processcontent yielded an increased positive correlation, r = .57, p< .001.

Detectionof Possible Misconceptions

Generatedanalogies and an analysis of qualitative data focusing onsimilarities and differences between analog and target conceptsrevealed a number of misconceptions. These misconceptions wereprimarily about the particulate nature of matter during heatconduction. Four general misconceptions were found in multipleconduction analogies. Table 7 summarizes the frequency and percentageof occurrence of each.

Table7

Conduction Analogies With Varying Misconceptions, n = 44*

* Some analogies showed morethan one misconception.

Thefirst misconception indicated that the difference between a good anda poor conductor was due to the presence or absence of particles insolids. A good conductor was composed of a lot of particles (e.g., aball pit full of balls) while a poor conductor had no particles(e.g., empty ball pit). One related misconception, found in oneanalogy, dealt with particle size. In this analogy, a good conductorwas composed of smaller particles than a poor conductor was (tennisballs versus basketballs). This particular analogy also had thetennis balls in a hot room while the basketballs were in a cold room.

Heatgenerated from within particles, rather than heat transference, wasanother misconception found in multiple analogies. For example, oneanalogy comparing people to particles noted how people get angry ifthey are bumped, thereby generating internal, “emotional heat.”

Thethird misconception related to the position of the particles insolids. Rather than having the particles of the solid vibrating in afixed position, these analogies had particles moving from place toplace. Both good and poor conductors had individuals (usually less ina poor conductor) running around a room (e.g., gym, classroom) orplaying a game (e.g., football, tag).

Thefinal misconception was that volume determined conductivity. In theseanalogies, good conductors had smaller volumes than poor conductors(e.g., a classroom versus a gymnasium). One subject even noted in theaccompanying explanation that the way the source and target weresimilar was, “[V]olume varies in both.”

Itcould be hypothesized that elaboration about the similarities anddifferences between the analog and target could mediate possiblemisconceptions. However, an examination of subjects’explanations showed a tendency to target obvious, superficialdifferences rather than substantive differences between the analogand target. For example, one generated analogy likened a goodconductor to a full elevator while its companion compared a poorconductor to an empty elevator. When asked to explain how the sourceand target concepts were different, the subject only noted,“Elevators and conductors are different.” Anotherindividual who generated analogies comparing good and poor conductorsto a full and an empty ball pit respectively, noted that thedifference between the source and target was, “You can actuallytouch the balls and demonstrate.” With one pair of analogieswhere volume-change was seen, the subject wrote that the differencebetween the analog and target was that, “Students are muchlarger than particles.” There was also one explanation where itwas questionable whether the subject understood that humans could beclassified as matter. When asked to indicate the difference betweensource and target, this subject wrote, “Particles are all piecesof matter, kids are not.”

Itwas easier for subjects to generate analogies for the layers of theEarth than heat conduction. These analogies primarily involved food,a trend previously found in analogies commonly used to convey theEarth’s layered interior (Nottis, 1999). Analogies that weregenerated for the Earth’s layered interior were also more validthan those for heat conduction were. There are a number of possibleexplanations for these findings. The first relates to content;relevant content knowledge and aspects of the content itself.

Previousresearch has found that the ability to generate a personal analogy tohelp understand an unfamiliar concept is mediated by the quality ofthe learner’s prior knowledge (Zook & Roller, 1996).Although subjects were given background content, the depth andquality of their prior knowledge may have varied for content areas.This, in turn, may have compromised the subjects’ ability toeffectively use the information that was provided.

Misconceptionsabout the particulate level of matter have been detected in children(DeVos & Verdonk, 1987), pre-college students (AmericanAssociation of Physics Teachers, 1996) and pre-service teachers(Gabel, Samuel, & Hunn, 1987). For example, children have beenfound to ascribe macroscopic qualities such as color and taste toparticles (DeVos & Verdonk, 1987). The classification of mattercan also be difficult to understand and misconceptions have beendetected in children in that area as well (Stavy, 1991). It isreasonable to assume that ideas labeled as misconceptions may havealso been a part of the prior knowledge of the current sample,especially since analogies generated for heat conduction appeared tocontain misconceptions previously identified in the literature. Theseincluded particulate level matter having macroscopic properties andanthropomorphic qualities (e.g., particles moving “[B]ecausethey are ‘uncomfortable’ from the heat,” or gettingemotionally “hot” because they have been bumped). It may besignificant that both institutions required, at most, two sciencecourses, which may have resulted in subjects drawing upon middle andhigh school science knowledge.

Theinability of subjects to articulate definitive differences betweenthe source and target concepts suggests that in presenting an analogyto future students, the subjects might not discuss their limitations.This could lead to additional misconceptions. This lack ofelaboration has important implications for using analogy teachingmodels which require the articulation of the limitations as part ofthe instructional process (e.g., Glynn, 1994).

Inaddition to prior knowledge issues, there is also the visualizabilityof the concepts. Certain content areas seem to be more easilyvisualized than others are. Although the layers of the Earth may notbe directly visible, examples of layering can be found in topography,food, and everyday materials. It was because of commonplace examplessuch as these that two outside reviewers concurred with theresearchers that “layers of the Earth,” although notobservable, could be classified as “visualizable.” Thisvisualizability seemed to make the Earth’s interior structuremore concrete to pre-service teachers, possibly contributing to theease with which analogies were generated.

Althoughthe result of heat conduction can be felt, the process is not aseasily visualized. The continuous vibration of unseen particles inmatter, as well as their movement and subsequent bumping from anenergy source appear to make conduction a more theoretical concept.These multiple, unobservable aspects, as well as the lack of everydayanalogs, may have contributed to the difficulty pre-service teachershad understanding heat conduction, ultimately compromising theirability to generate effective analogies which showed the differencebetween good and poor conductors.

Thesecond possible explanation for the disparity in scores betweenanalogies generated for the layered structure of the Earth (structureconcept) and those generated for heat conduction (process concept)relates to subjects’ level of thinking. More than contentknowledge is needed to generate effective analogies. Bloom (1956)categorized cognitive objectives into six major levels of increasingcomplexity -- knowledge, comprehension, application, analysis,synthesis, and evaluation. In order to generate valid analogies,students must have the ability to generalize information learned foruse in other situations (application), break down course content intocomponent parts so that relationships can be determined andunderstood (analysis), see the parts and construct the whole(synthesis), and judge the value of the material to determine itsusefulness for future applications (evaluation) (Jacobs & Chase,1992). In the current study, it appeared as if subjects tended to uselower order thinking skills such as basic knowledge andcomprehension to generate analogies. This may explain whyanalogies generated for more concrete structure content werecompleted more successfully than those generated for process content.

Anotherrelated explanation for the score disparity, and worthy of furtherexamination, is the level of reflective judgement needed to generatevalid analogies for abstract and/or complex concepts. King andKitchener (1994) have identified three levels (seven stages) ofreflective judgment. Using the researchers’ criteria, it wouldseem that a pre-reflective person could generate valid analogies forwhat has been designated as structure content whereas an individualwould need to be at least quasi-reflective, with an understandingbeyond concrete instances, to generate valid analogies for what hasbeen labeled process content.

Problemswith scoring the analogies could also account for differences foundin scores. Inter-rater reliability was lower for scoring process thanstructure analogies. The current scale may need to be refined for usewith more theoretical and/or complex concepts. It may be that thecomplexity of some of the concepts should be addressed in anotherkind of scale. Development of a group of scored sample analogiesmight also help. A related scoring issue ties to the body ofscientific knowledge and whether all previously identifiedmisconceptions would clearly be identified as such at all levels ofscience instruction. This may have been a factor in some of themisconceptions about particulate matter found in the conductionanalogies.

Thethird identified misconception was that particles in solids movearound a given space. An elementary level understanding of particlesin solids notes, “[T]he particles are arranged in regularpatterns, with each particle being able only to vibrate around afixed position” (DeVos & Verdonk, 1996, p. 659). However,conduction in solids comes from two mechanisms, the vibration of aparticle in a comparatively fixed position, taught at the elementarylevel, and the movement of free electrons. Metals are known to bebetter conductors due to having free (valence) electrons that movethroughout the substance (Long, 1988). It is the free electrons thatcontribute the majority of their conductivity. Therefore, those whogenerated analogies where particles moved from place to place werenot completely wrong at all levels of understanding but needed toproperly identify the aspects analogous to electrons and atoms.However, it should be noted that in no analogy or accompanyingexplanation was the term “electron” used.

Theissue related to particle movement suggests the need for anassessment of subjects’ prior knowledge, providing clearerbackground information where critical concepts are highlighted, andan alternative scoring rubric where analogies having particlesvibrating in place and particles moving around receive maximum scoresif electrons and atoms are correctly identified in accompanyingexplanations. A highly valid analogy might be redefined to providefor both mechanisms with recognition that, depending upon theconductor, one mechanism would be dominant over the other. Anaccompanying scoring manual with exemplars of highly valid heatconduction analogies might also eliminate some of the interpretationdifficulties.

Theuse of analogies has been promoted in the professional literature(Thiele & Treagust, 1991). However, not all analogies are equallyeffective. Preliminary results from this study indicated that thetype of concept appeared to affect analogy generation. Althoughanalogies can help students understand nonvisible and theoreticalconcepts (Lawson, 1993), it was for heat conduction, categorized as amore abstract, process concept, that pre-service teachers had themost difficulty generating valid analogies.

Teachingabstract, intricate information about the particulate level of matteris difficult, even at the secondary level (DeVos & Verdonk,1996). Therefore, it is important to further investigate the sourceof pre-service teachers’ difficulties. Future studies shoulddetermine whether their difficulties stemmed from a lack of priorknowledge, the persistence of alternative conceptions, the absence ofaccessible analogs, the evaluation tool used, or a need forhigher-order thinking skills and higher levels of reflectivejudgement.

Resultsof this analysis have important implications for pre-service teachereducation programs. First, it would seem that there is a need toprovide pre-service teachers with adequate science content knowledge.Pre-service teachers need enough knowledge to generate validanalogies. In addition, science-related courses should considerexamining some of the prior knowledge of pre-service teachers so thatrecurrent misconceptions can be addressed in those courses. Analogiesshould be presented as pedagogical tools requiring a structured,systematic presentation. When teaching about and modeling recommendedinstructional models, science content known to be susceptible tomisconceptions should also be incorporated.

Second,it appears as if pre-service teachers may need instruction inhigher-order and reflective thinking skills. Teacher preparationprograms should consider the inclusion of such activities in the areaof science. Prospective teachers need to know how to get moreinformation from what they are learning and reading rather thanmemorizing facts. Both increased science knowledge and instruction inhigher-order and reflective thinking skills would presumably preparepre-service teachers for increased standards and expectations inschool systems. This two pronged approach should also facilitate andimprove the use of science analogies throughout a teacher’scareer.

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We would like to thank Dr. James W. Baish, Professor of Mechanical Engineering,Bucknell University, who provided feedback on the misconceptionsfound in the conduction analogies and Gary N. Nottis, GN Geophysical,Lewisburg, PA who provided additional feedback on the manuscript.Correspondence concerning this article should be addressed toKatharyn E. K. Nottis, Department of Education, Bucknell University,Lewisburg, PA 17837. Electronic mail may be sent via Internet toknottis@bucknell.edu.

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