The Associations Between Language Aptitude and Second Language Grammar Acquisition

24 Pages·2015·0.58 MB·English

Applied Linguistics 2015: 36/3: 385–408 (cid:2) Oxford University Press 2014
doi:10.1093/applin/amu054 Advance Access published on 7 October 2014
The Associations Between Language
Aptitude and Second Language Grammar
Acquisition: A Meta-Analytic Review of
Five Decades of Research
D
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SHAOFENG LI e
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AppliedLanguage Studies andLinguistics, TheUniversity ofAuckland, Auckland, m
New Zealand h
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E-mail:[email protected] s
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Thisstudyreportsameta-analysisthatsynthesizestheempiricalresearchonthe de
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role of language aptitude in second language grammar acquisition. A total of ic
33studyreportswereidentifiedincluding17predictivestudiesthatinvestigated .o
u
the correlations between aptitude and ultimate L2 attainment and 16 inter- p.c
actionalstudiesthatexaminedtheinterfacebetweenaptitudeandtheeffective- om
ness of instructional treatments. These studies generated 309 effect sizes and /a
p
imSnuovbodsleevrqeaudteen3at,1sms0o6ocidaLet2rioantloerawraninteharsly.Ls2Iist gdwreaammsomfnoasutrrnadlteeadtrhnatihtnagat,phtriit=guh.d3es1c,hsh9oo5ow%l setduCdIae=nn.t2os5vw–e.re3ar6le.l plij/article
more likely to draw on aptitude than university students and that aptitude -a
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wasmorestrongly correlatedwithexplicittreatmentsthanimplicittreatments. stra
Theroleofaptitudewasmoreevidentforyoungerlearnersthanolderlearners c
inpredictivestudieswhereastheoppositewastrueininteractionalstudies.The t/36
resultssuggestthatlanguageaptitudeasmeasuredviatraditionalaptitudetests /3/3
is a set of cognitive abilities that were more implicated in initial stages of L2 8
5
development and conscious learning conditions. The findings are valuable to /2
4
2
resolving somelong-standing controversies surroundinglanguage aptitude. 2
4
5
6
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INTRODUCTION y g
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Languageaptitudehasbeenfoundtobeoneofthemostimportantindividual st o
difference variables in second language acquisition (SLA) (e.g. Cochran et al. n
0
2010).1 Since the inception of aptitude research in the 1950s, marked by the 9 A
p(MubLlAicTa)t,i2onthoefreCahrarosllbeaennd Sanapoanbu’sn(d2a0n0c2e)oMfoedmerpniriLcaalngruesaegaercAhptiintudveariToeusst pril 2
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1
instructionalsettingsandwithlearnersofdifferentagegroups.Relatedstrands 9
of research include validation of aptitude tests, the associations between
aptitude (usually with other variables such as strategies or intelligence) and
aspects of L2 proficiency, the impact of aptitude on the effects of instructional
treatment, the role of aptitude in different instructional settings, and therela-
tionship between aptitude and age. Despite the prolific empirical research
accumulated over the past 50 years, exactly how aptitude relates to SLA
386 META-ANALYSISOFAPTITUDEANDL2GRAMMARACQUISITION
remainsunclearbecauseofthedifferencesanddisparitiesbetweenthefindings
of the primary research.
There has also been theoretical evaluation of the role of aptitude. A main
controversy has centered on whether the role of aptitude is only manifest in
conscious learning. Krashen (1981) argued that the bulk of SLA relies on im-
plicit processing of available linguistic input and that ‘what is considered
D
secondorforeignlanguageaptitudemaybedirectlyrelatedtoconsciouslearn- o
w
ing’(Krashen1981:158).WhileKrashen’sdismissalofconsciouslearninghas n
lo
beenchallenged,therehasbeennoanswertohisdoubtabouttherelevanceof ad
e
aptitude to conditions amenable to implicit learning, such as that in natural- d
isticsettingsintheabsenceofformalinstruction.Inlightoftheimportanceof fro
m
aptitude,thecopiousempiricalresearch,andthemanyunansweredquestions, h
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the time is ripe for a meta-analysis that is able to provide an estimate of the s
association between aptitude and SLA and account for the between-study ://a
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variation pertaining to the association. d
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DEFINITIONS AND CHARACTERISTICS OF LANGUAGE p
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APTITUDE m
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Trreehfseleeracertchhda,ifvfaeenredbnetpeenadpaptgwrooogaycr.heepAsrcetcsooerntdhtianistgivceotogdnCeitfaiivrnreiotilcolonnasnstdorufSclatapniongnurae(gl2ae0ti0oa2np)t,ittoluadnthegeutoahrgayet, plij/article
aptitude refers to a set of cognitive abilities that are ‘predictive of how well, -ab
s
relative to other individuals, an individual can learn a foreign language in a tra
c
given amount of time and under given conditions’ (Carroll and Sapon 2002: t/3
23). Central in this view is the predictive power of aptitude and its link with 6/3
ultimate L2 attainment, irrespective of instruction type and learning context. /38
5
Underlying such a perspective is Carroll’s (1963) preference for an eclectic /2
4
approach to language instruction: there is no need to tailor instruction to ac- 2
2
4
commodate individual differences. The pedagogical value of Carroll’s concep- 5
6
tualization of aptitude and the instruments used to measure it lies in its b
y
(primary) prognostic function of foretelling a learner’s chances of success in gu
e
meeting a criterion and its (secondary) diagnostic function of detecting learn- st o
ing disabilities. This constitutes a product-oriented, static view of language n
0
aptitude. 9
A
A different stance is held by Robinson (2005), who considered language p
aptitude as ‘cognitive abilities information processing draws on during L2 ril 2
0
1
learning and performance invarious contexts and at different stages’ [emphases 9
added] (Robinson 2005: 46). Robinson’s definition reflects a process-oriented,
dynamic view of language aptitude and is derived from Cronbach and Snow’s
(1977) argument that aptitude is sensitive to environmental factors and is
eitheractivatedorinhibitedasafunctionofthepropertiesofdifferentlearning
conditions. Thus, no instruction/treatment is effective for all learners, and
maximal effects are achievable only when there is a fit between a learner’s
S.LI 387
cognitive profile and the characteristics of the instructional context.
Instruction, therefore, should be adjusted or modified to cater to learners’
variation in aptitude.
Despite the different views with regard to how aptitude relates to the out-
come and process of L2 learning as represented in the above two definitions,
both were based on the postulation that language aptitude consists of a set of
D
cognitive abilities that are (i) relatively immutable, (ii) distinct from intelli- o
w
genceandotherindividualdifferencevariables(e.g.motivation),and(iii)nota n
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learning achievement. These characteristics of aptitude, however, only apply a
d
e
to cognitively mature learners, not child learners whoseperformance on apti- d
tude measures such as the MLAT-elementary (MLAT-E) may improve as a fro
m
function of age. It is worth noting that while SLA researchers tend to agree h
withthe‘aptitudeascognitiveabilities’ axiom,thecontentandcharacteristics ttps
of aptitude are conceiveddifferently in educational psychology. Snow (1991), ://a
c
for example, contended that aptitude can be any measureable characteristic ad
e
‘propaedeutic’(‘requiredaspreparationforalearningcondition’)(Snow1991: m
ic
205) to a learning goal, including affective (feelings and emotions), conative .o
u
(motivation),andcognitive(reasoningandmemory)variables.Asimilarview p
.c
ofaptitudetothatofSnowwasevidentinhowaptitudewasoperationalizedin om
the Pimsleur Language Aptitude Battery (PLAB), which included ‘attitude /a
p
p
toward the target language’ as a component of language aptitude. In this lij/a
meta-analysis, aptitude is conceived as a cognitive variable that is distinct rtic
from affective and conative variables. le
-a
b
s
COMPONENTS AND MEASURES trac
t/3
6
To date, there has been little theorization about what pieces the aptitude /3
/3
puzzleshouldinclude that areessentialtoSLA,andthe‘standard’set ofcom- 8
5
ponents have, by default, been those measured by the MLAT, the most influ- /2
4
ential aptitude measure dominating current aptitude research. The MLAT 22
4
includes five subtests that were claimed to measure three aptitude compo- 56
nents: phonetic coding, language analytic ability, and memory, which were by
g
believed to be essential to the learning of pronunciation, grammar, and u
e
vocabulary, respectively. The MLAT was developed based on Carroll’s obser- st o
vations about how languages were learned/taught during that time (1950s), n 0
and some of the subtests consist of learning tasks that were identical with 9 A
othresimPailiarerdtoAtshsoosceiattehsatshuabptepsetnerdeqiunirfeodreiagntelastn-gtaukaegre ctolassmese;mfoorrizeexaamplliest, pril 2
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1
of words in an unknown language and their English translations and recall 9
afterward.Othermeasuresofaptitude(e.g.PLAB,DLAB,VORD,LLAMA,and
CANAL-F)havebeencreatedforvariouspurposes,buttheywereeithermod-
eled on or validated with reference to the MLAT and did not demonstrate
higher predictive validity.
Nevertheless, criticism of the MLAT has never ceased, mainly on the
grounds that it was developed based on audiolingual teaching characterized
388 META-ANALYSISOFAPTITUDEANDL2GRAMMARACQUISITION
by mechanical drills and rote learning and was couched in a Behaviorist view
of learning. The extent to which it is sensitive to learning in more communi-
cativeapproachesisarguablyquestionable.Oneproposedchangeistoincorp-
orateanelementofworkingmemory,whichisrequiredfortheonlinestorage
andprocessingoflinguisticstimuli.However,theadditionofworkingmemory
as an aptitude measure has only been considered theoretically, and little em-
D
pirical research has been undertaken to validate working memory as an apti- o
w
tude component or to map the relationship between working memory and n
lo
other aptitude components (but see *Roehr and Ga´nem-Gutie´rrez 2009). For a
d
e
instance, the question of whether the phonological loop of working memory, d
whichisresponsibleforstoringandrehearsingverbalinput,isdistinctfromor fro
m
isomorphic with the memory and phonetic coding components in traditional h
aptitude tests remains unresolved. ttps
AnotherweaknessoftheMLATandsimilartestsimpedingaptituderesearch ://a
c
isthefuzzyunderlyingconstructs.Thiscriticismisjustifiableontwoaccounts. ad
e
First, the test was validated only empirically (based on the data from over m
ic
5,000 foreign language learners) but not theoretically in that it was not .o
u
guided by any second language learning theory. Secondly, the five subtests p
.c
do not correspond with the three hypothesized aptitude components, which om
makes it difficult to meaningfully interpret the related findings. For example, /a
p
p
based on Carroll’s speculations (1981), the Number Learning subtest of the lij/a
MLAT measures three cognitive abilities, namely memory, auditory alertness, rtic
and inductive language learning ability/analytic ability. le
-a
b
s
TWO BROAD LINES OF APTITUDE RESEARCH trac
t/3
6
As discussed above, language aptitude was defined in two subtly different /3
/3
ways: as a variable that is predictive of ultimate L2 attainment and one that 8
5
interactswithcontextualfactorsinaffectingL2outcomes.Thetwodefinitions /2
4
are reflected in two parallel tracks of empirical research: predictive and inter- 22
4
actional. A side-by-side comparison of the two types of research can be seen 56
in Table 1. Within predictive research, a substantial number of studies inves- by
g
tigated the correlation between high school and university students’ aptitude u
e
scores and end-of-semester course grades or scores on proficiency tests. Some st o
of the studies included other individual difference variables together with ap- n 0
titude, and in general, aptitude was found to be the best predictor (Cochran 9 A
Aet aslu. b2s0e1t0)ofanpdreddisictitnivcet frsotumdieostheurtivliazeridabltehse(*cGoanrcdenpetr oafndapLtaimtubdeertt1o96te5s)t. pril 2
0
1
Bley-Vroman’s (1990) Fundamental Difference Hypothesis which stated that 9
children draw on domain-specific, implicit language acquisition mechanisms,
whereas adults resort to domain-general problem-solving cognitive abilities.
Thesestudiestypicallyinvestigatednaturalisticlearnersandsoughttodemon-
stratethatlanguageaptitudewasonlypredictiveoftheL2achievementoflate
starters,notofthoselearnerswhostartedtolearnaforeign/secondlanguagein
childhood.
S.LI 389
Table 1: Predictive and interactional aptitude research
Predictive Interactional
Purpose To investigate how aptitude To examine how aptitude
relates to ultimate L2 mediates the effects of in-
outcomes structional treatments
D
Overall design Correlating aptitude scores Correlating aptitude scores o
w
with end-of-semester withposttestscoresorgain n
lo
grades or scores of profi- scores after treatment a
d
ciency tests e
d
Control of previ- No, participants take one- Yes, through pretesting fro
ous knowledge shot tests m
Linguistic focus Nostfrouccutsuroens specific Tresaptemciefinctslinanguditsetisctstaforgcuetsson https
Participants A whole cohort of students Learners are divided into ://a
c
several groups and receive ad
e
different instructional m
treatments ic
.o
Pedagogical up
implications (cid:2) Selection of elite (cid:2) Learners with different .com
learners aptitude profiles may /ap
(cid:2) Wreqauiviirnegmelanntgsuage btyepneesfiotffrionmstrudicftfieornent plij/a
(cid:2) Instruction should be rtic
le
adapted to cater to -a
differences in learners’ bs
aptitude tra
c
t/3
6
/3
/3
8
5
Interactional studies are experimental, and a prominent feature of these /2
4
2
studies is the investigation of the comparative effects of different treatment 2
4
types [e.g. explicit vs. implicit in *Sheen (2007) or inductive vs. deductive in 56
*Hwu and Sun (2012)] and how the effects were related to one or more ap- by
g
titude components or global aptitude scores. The instructional treatments are u
e
characterizedbyconsistentmanipulationofvariablesanduseoffocusedtasks/ st o
tests that target one or several particular linguistic structures (which contrasts n 0
with predictive studies where learners were not tested on their knowledge or 9 A
uclsaessorfopoamrtiwcuhlearresitnrustcrtuucrteios)n.Iwnatesrdaecltiivoenraeldsttuodleieasrnweerrseincagrrroieudposu(*tSehiteheenr2in00th7e) pril 20
1
orinalaboratorysettingwherelearnersreceivedinstructiononanindividual 9
basis (*Li 2011) or via the computer (*Robinson 1997).
OBJECTIVES OF THIS META-ANALYSIS
The current meta-analysis sought to explore the relation of language aptitude
to L2 grammar (morphosyntax) acquisition by synthesizing related empirical
390 META-ANALYSISOFAPTITUDEANDL2GRAMMARACQUISITION
research. The criterion variable was restricted to grammar learning because
(i) grammar was the most frequently studied among the three aspects of L2
competence (the other two being pronunciation and vocabulary), (ii) the re-
lationofaptitudetogrammarlearninghasbeenacentralthemeintheoretical
discussions on the role of aptitude in SLA, and (iii) space constraint makes
it impossible to include all measures of L2 competence.
D
Byusingrigorousstatisticalprocedures toaggregatetheresults(effectsizes) o
w
from primary studies, this meta-analysis seeks to provide a numeric estimate n
lo
of the role of the construct and resolve the disparities in the findings of the ad
e
aapimtitsutdoeesxtaumdiiense. tAhseidiempfraocmt oeffsfeecvtersaizlepoatgegnrteigaaltmioond,etrhaitsinmgevtaar-iaanbalelyssoisnatlhsoe d from
role of language aptitude in L2 grammar learning. These variables include the h
ttp
setting(highschoolvs.universityvs.naturalistic),age,explicitnessofinstruc- s
tion,andresearchcontext(classvs.lab).Thedecisiontoexaminethesemeth- ://ac
a
odological features as moderators was based on the observation that they d
e
m
constituteddefiningcharacteristicsoftheincludedstudiesandthatinprevious ic
meta-analyses in applied linguistics they have been found to mediate SLA .ou
p
processes. .c
o
This meta-analysis sought to answer the following research questions: m
/a
p
21 WWWhhhaaattt ifsiascthtotehrseromlreeelodafitailotaennsgithusiaprgoelbeae?ptwtiteuedne ilnanuglutiamgeateapLt2itgurdaemmanadr atchqeuiseiftfioecnt?s plij/article
of different instructional treatments? What factors moderate this -ab
s
relationship? tra
c
t/3
6
/3
/3
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METHOD 5
/2
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Identifying primary research 2
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The related primary studies were located through five commonly used search b
y
strategies(Lietal.2012)includingexaminingthereferencesectionsofprimary g
u
e
studies, computer search, checking bookshelves in the library, seeking advice s
t o
from authorities, and emailing authors to retrieve unpublished studies. The n
0
databases searched include LLBA, MLA International Bibliography, ERIC, 9
A
PsychINFO, ProQuest Social Science Journals, Social Sciences Citation Index, p
PsycARTICLES, and ProQuest Dissertations and Theses. During the searches, vari- ril 2
0
1
ous combinations of the following key words were used: aptitude, language 9
aptitude, cognitive aptitudes, MLAT, language analytic ability, phonetic coding, rote
memory,secondlanguageacquisition/learning,andforeignlanguagelearning.Atotal
of 67 studies were identified that investigated the relationship between lan-
guage aptitude and some aspects of second language acquisition. In all, 33 of
the studies included grammar learning as a criterion variable and these were
selected for this meta-analysis.
S.LI 391
Selection criteria
Given that the MLAT is the most influential aptitude test that marked the
beginning of aptitude research, only studies conducted since its publication3
were included in this meta-analysis. Studies published after May 2013 (my
cutoff point for data collection) were not included. With regard to aptitude
measures,thismeta-analysisincludedallstudiesthatusedtraditionalaptitude D
o
measures including test batteries with the same or similar components to the w
n
MLAT (such as PLAB, VORD, DLAB, and LLAMA), translated versions of the lo
a
d
MLAT in other languages, and tests that only measure one aptitude compo- e
d
nent. Whereas the aforementioned criteria relate to the predictor variable, fro
m
selection criteria relating to measures of grammar learning concern the criter-
h
ion variable. To be eligible for inclusion in this meta-analysis, a study had to ttp
s
contain a measure of L2 grammar knowledge or use, including both focused ://a
(targeting one or several specific grammar structures; typical of interactional ca
d
studies)andunfocused(tappinggeneralgrammarknowledgewithoutafocus; e
m
typical of predictive studies) grammar tests. With respect to research design, ic
.o
only studies reporting correlation coefficients (r) were included; results based up
on factor analysis, multiple regression analysis, or structural equation model- .co
m
ing analysis were not meta-analyzable and were therefore excluded. Also, /a
p
studies investigating special learners (e.g. those with learning disabilities) p
were not included. To minimize publication bias, the fact that studies with lij/a
statistically significant results are more likely to be published or submitted rticle
forpublication,thismeta-analysisincludedbothpublishedstudiesandunpub- -a
b
s
lished Ph.D. dissertations. tra
c
t/3
6
Coding /3
/3
8
An overarching principle adhered to in this study is that data coding (and 5
/2
analysis) must be both empirically feasible and theoretically meaningful. 4
2
2
Oneexampleofsuchaprincipleisthedecisiontoclassifyallidentifiedstudies 4
5
as either predictive or interactional, depending on whether it investigated the 6 b
y
relationofaptitudetotheendproductofgrammarlearningortheeffectiveness g
u
ofinstructionaltreatments.Thedecisionwasbasedonthepreviouslydiscussed e
s
different roles of aptitude (Table 1) and on the observed characteristics of the t o
n
twodistinctparadigmsofresearch.Includingallstudiesinthemoderatorana- 0
9
lysis would have been statistically desirable because of the resultant larger A
p
sample size but it would have been theoretically unsound to do so. ril 2
The protocol for coding aptitude measures appears in Table 2 and is further 01
9
elaborated below:
1 Complete test batteries with several subtests (MLAT, PLAB, etc.) retained
their names, and versions of the MLAT and PLAB in other languages
were labeled Quasi-MLAT and Quasi-PLAB, respectively. The MLAT
Short consists of the last three subtests and was coded as MLAT because
it was said to have the same predictive and construct validity as the
392 META-ANALYSISOFAPTITUDEANDL2GRAMMARACQUISITION
Table 2: Coding protocol for aptitude measures
Codes in meta-analysis Measures in primary studies
Original labels MLAT, EMLAT, PLAB, LLAMA
Quasi-MLAT, Quasi-PLAB MLAT and PLAB in other languages
Phonetic coding ability MLAT 2, PLAB 5 & 6, LLAMA-D & LLAMA-E, cor- D
o
responding subtests of MLAT and PLAB in other w
n
languages lo
a
Language analytic ability MLAT 4, PLAB 4, LLAMA-F, Language Analysis Test d
e
OPLttAo´B(2in00o2t)h,ecrolrarnesgpuoangdeisng subtests of MLAT and d fro
m
Rote memory MLAT 5, LLAMA-B, corresponding subtests of MLAT h
and PLAB in other languages ttps
Original labels MLAT 1, MLAT 3, MLAT 4+5 ://a
c
a
d
e
Note: MLAT: Modern Language Aptitude Test; EMLAT: MLAT for elementary students, also m
known as MLAT-E; MLAT 1: Number Learning; MLAT 2: Phonetic Script; MLAT 3: Spelling ic.o
Clues; MLAT4: Words in Sentences; MLAT 5:Paired Associates; PLAB: ThePimsleur Language u
p
Aptitude Battery; PLAB 3: Language Analysis; PLAB 5: Sound Discrimination; PLAB 6: Sound- .c
o
Symbol Association; LLAMA B: Vocabulary Learning; LLAMA D: Phonetic Memory; LLAMA E: m
Sound-Symbol Correspondence; LLAMA F: Grammatical Inferencing. /ap
p
lij/a
full-length MLAT (Carroll and Sapon 2002). By the same token, the com- rtic
le
bination of parts B, E, and F of the LLAMA was coded as LLAMA. -a
b
2 Tests that were combinations of several components (e.g. MLAT 4+5 in stra
Robinson 1997) were recorded intact. c
t/3
3 With respect to the coding of aptitude components, phonetic coding 6
/3
ability was represented by MLAT 2, PLAB 5 and 6, and LLAMA D and /3
8
E; language analytic ability by MLAT 4, PLAB 4, LLAMA F, and the 5
/2
Language Analysis Test by Otto´ (2002: cited in *Sheen (2007)); rote 42
2
memory by MLAT 5 and LLAMA B. The coded aptitude components 4
5
6
also consisted of the subtests of the MLAT and the PLAB in other lan- b
y
guages. Subtests that do not clearly measure a single cognitive ability g
u
were not further coded as aptitude components, such as MLAT 3, e
s
which Carroll said may measure both phonetic coding ability and t o
n
English vocabulary. 0
9
A
p
Learners’ age was entered as reported by primary researchers. In the event ril 2
0
1
that information about the average age of a sample was unavailable, other 9
information was used to infer the age of the participants, such as taking the
median of a range. In the data set, there was a group of age-related studies,
whose primary purpose was to verify the hypothesis that aptitude was only
implicatedinadultSLA.Thesestudiesprovidedtwotypesofinformationabout
participants’ age: one related to the actual age of the learners when they
participated in the study, which can be called ‘age of testing’, and the other
S.LI 393
toarange(e.g.(cid:3)13)duringwhichlearnersstartedtolearntheL2,whichcan
be called ‘age of onset’. The ‘age’ variable codedin this meta-analysis was age
of testing, not age of onset.
In interactional studies, an instructional treatment was coded as explicit
or implicit depending on whether it contained elements that drew learners’
attention to linguistics forms. Explicit treatments refer to any instruction that
D
contained metalinguistic information (e.g. *Carpenter 2008) or information o
w
about the unacceptability of an L2 utterance (e.g. *Yilmaz 2013); these also n
lo
include instruction intended to facilitate learners’ awareness of the target ad
e
structure such as the rule-search condition in Robinson (*1997), where lear- d
ners were required to find the grammar rule exemplified in the provided fro
m
linguistic data and the computerized recasts in Trofimovich et al. (*2007), h
which were provided following the formula: learner production+re- ttps
cast+form-focusing device (learner asked whether he/she noticed the differ- ://a
c
ence between the recast and his/her own production). An instructional ad
e
treatment was coded as implicit if there was a lack of a form-focusing device m
ic
andlearningwasintendedtobederivedfromexposuretolinguisticexemplars .o
u
only. These include purely comprehension-based instruction such as Lee p.c
o
(*2008) and Carpenter (*2008) and interaction-based instruction incorporat- m
ing implicit corrective feedback (e.g. recasts) such as Li (*2011). /ap
p
A related variable that overlaps with the explicit–implicit distinction is lij/a
research context: whether a study was conducted in the laboratory or the rtic
classroom. Both explicit and implicit instructional treatments can be imple- le
-a
mented in either a laboratory or classroom context. However, in general, b
s
laboratory treatments tend to be more explicit than classroom treatments be- tra
c
causeinthelaboratory,instructionisindividualized,thelearnerislesssubject t/3
6
to distraction, and the intention of the instruction is more easily perceived. /3
/3
8
5
Analysis /24
2
2
4
The basic unit of analysis is the Fisher’s z-score transformed from the correl- 5
6
ation coefficients (r) extracted from each included study. Fisher’s z was then b
y
transformedbacktorinreportingtheresults.Fisher’sz(anditsvariance)was g
u
e
used instead of r because it has better statistical properties such as normal s
distribution and stable variance. Fisher’s z was calculated via the following t on
0
formula: 9
A
z ¼0:5(cid:4)ln(cid:2)1þr(cid:3) pril 2
1(cid:5)r 01
9
Aswithmost meta-analyses, thisstudyfollowedthetypical procedureof con-
ductinganoverallanalysisfortheconstructunderinvestigation,whichmight
be referred to as effect size aggregation, followed by moderator analysis
that aims to identify factors that account for consistent variation of the effect
sizes within the sampled population. A random-effects model was used for
effect size aggregation and a mixed-effects model for moderator analysis.
394 META-ANALYSISOFAPTITUDEANDL2GRAMMARACQUISITION
Only categories with more than three effect sizes were subjected to effect size
aggregation and moderator analysis; a regression analysis was not pursued
if there were less than five cases for the predictor variable. In effect size
aggregation, a within-group Q value (Q ) was calculated for each group of
w
effect sizes as a measure of homogeneity. For moderator analysis, between-
group Q tests (Q ) were utilized for categorical variables and meta-regression
b D
analyses were performed for age, a continuous variable. o
w
n
lo
a
d
e
d
RESULTS fro
m
Study characteristics h
ttp
s
A total of 33 study reports were identified that examined the role of language ://a
aptitude in second language grammar acquisition (Table 3). (Due to limited c
a
d
space,informationregardingthemethodologicalandsubstantiveaspectsofthe e
m
studies was included as Supplementary Data available at Applied Linguistics ic
.o
online). Among them, 17 were predictive studies and 16 were interactional u
p
studies; 23 were journal articles or book chapters and 10 were Ph.D. disserta- .co
m
tions.Toexplorepublicationbias,thatis,whethertherewerestudiesthathad /a
p
not been retrieved and would have affected the results, a fail-safe N was p
calculated, z=12.12, p<.00, N=1,228. This suggests that 1,228 studies are lij/a
needed to nullify the results based on the current data set, and therefore it rticle
issafetostatethattheconstructunderinvestigationiswellrepresentedbythe -a
b
s
included studies. tra
Theincluded studiescontributed309effectsizesandinvolved3,106second ct/3
language learners. As can been seen from Figure 1, there has been a rapid 6
/3
increaseintheamountofempiricalresearchsince2007,inboththepredictive /3
8
5
and interactional domains, especially the latter. One distinctive trend is that /2
4
early aptitude research was mainly predictive, which is evidenced by the fact 2
2
4
that before 1995 there was only one interactional study [*Hauptman 1971, 5
6
whichinvestigatedhowaptituderelatedtotheeffectsofstructural(inductive) b
y
and situational (deductive) approaches inan audiolingual setting]. The recent gu
e
growthofpredictiveresearchwaslargelyattributabletotheburgeoningofage- s
t o
related studies (five out of the eight study reports that have appeared since n
0
2007 relate to age effects in SLA). 9
A
As Table 3 shows, the mean age of the participants of the studies is 24.4 p
years,buttheparticipantsinthepredictivestudieswereonaverageeightyears ril 2
0
1
older than those in interactional studies, with a rangeof 16–60 years. Further 9
examination of the data showed that by and large the gap was attributable to
thesubsetofage-relatedstudiesthattypicallyinvolvedolderlearners,withan
average age of 36.8 years. Whereas over one-third of the predictive studies
were age-related studies that investigated (older) naturalistic learners, the
majority of theinteractional studies wereconducted with university students,
and there were none with naturalistic learners.