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The influence of the place-value structure of the Arabic number ...

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Comparably, also <strong>the</strong> <strong>number</strong> <strong>of</strong> regressions from <strong>the</strong> result back to <strong>the</strong> summands was<br />

moderated by <strong>the</strong> requirement <strong>of</strong> a carry operation [F(1, 18) = 8.68, p < .01]: in carry addition<br />

problems participants looked back to <strong>the</strong> summands significantly more <strong>of</strong>ten than in non-carry<br />

problems (0.54 vs. 0.46 regressions, respectively). Additionally, <strong>the</strong> main effect <strong>of</strong> digit<br />

identity indicated that more regressions to <strong>the</strong> summands started from <strong>the</strong> decade digit as<br />

compared to <strong>the</strong> unit digit <strong>of</strong> <strong>the</strong> result. This was fur<strong>the</strong>r specified by <strong>the</strong> reliable two-way<br />

interaction <strong>of</strong> carry and digit identity [F(1, 18) = 17.24, p < .001]. <strong>The</strong> requirement <strong>of</strong> a carry<br />

specifically increased <strong>the</strong> <strong>number</strong> <strong>of</strong> regressions from <strong>the</strong> decade digit <strong>of</strong> <strong>the</strong> result back to <strong>the</strong><br />

summands (+ 0.15 vs. ± 0 regressions).<br />

Target <strong>of</strong> regressions: Examining <strong>the</strong> regressions from <strong>the</strong> second summand back to<br />

<strong>the</strong> first summand, <strong>the</strong> ANOVA showed a reliable effect <strong>of</strong> carry [F(1, 18) = 11.72, p < .01]<br />

with more regressions to <strong>the</strong> first summand for carry addition problems as compared to noncarry<br />

problems (0.58 vs. 0.44 regressions, respectively). Additionally, <strong>the</strong> main effect <strong>of</strong> digit<br />

identity was significant as well [F(1, 18) = 42.20, p < .001] indicating that <strong>the</strong> majority <strong>of</strong><br />

regressions was directed to <strong>the</strong> unit digit when looking back to <strong>the</strong> first summand (0.83 vs.<br />

0.19 regressions). Fur<strong>the</strong>rmore, <strong>the</strong> reliable interaction <strong>of</strong> <strong>the</strong>se two factors [F(1, 18) = 6.55, p<br />

< .05] implied that <strong>the</strong> increase <strong>of</strong> regressions towards <strong>the</strong> first summand due to <strong>the</strong><br />

requirement <strong>of</strong> a carry was more pronounced on <strong>the</strong> unit digit than on <strong>the</strong> decade digit <strong>of</strong> <strong>the</strong><br />

first summand (+ 0.13 vs. + 0.05 regressions, respectively).<br />

In line with <strong>the</strong>se results, <strong>the</strong> ANOVA evaluating <strong>the</strong> regressions from <strong>the</strong> result back<br />

to <strong>the</strong> two summands also revealed a significant carry effect [F(1, 18) = 27.22, p < .001]:<br />

more regressions from <strong>the</strong> results to <strong>the</strong> summands were observed for carry than for non-carry<br />

problems. Fur<strong>the</strong>rmore, also <strong>the</strong> two main effects <strong>of</strong> problem element [F(1, 18) = 18.42, p <<br />

.001] and digit identity [F(1, 18) = 26.21, p < .001] were reliable. This indicated that more<br />

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