The mnemonic keyword method: The effects of bidirectional retrieval ...

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M. Wyra et al. / Learning and Instruction 17 (2007) 360e371 365 Table 2 Variables tested on each level of the hierarchy Level Variable code Variable description Within-student OCCASION Testing occasions (0 ¼ occasion 1,., 4¼ occasion 5) LEARNING Dummy variable for learning occasion (1 ¼ occasion 2; 0 ¼ occasions 1, 3, 4 and 5) Between-student GENDER Sex of the student (0 ¼ male; 1 ¼ female) YRLEVEL Year level (0 ¼ Year 6; 1 ¼ Year 7) ACHIEV Teachers ranking of students’ academic achievement in class (1 ¼ highest achiever,., 29¼ lowest achiever) TREATMNT Treatment (0 ¼ control group; 1 ¼ experimental group) VVIQ Total score for the VVIQ questionnaire i.e. vividness of images (29 ¼ lowest,., 80¼ highest) AMI Total score for AMI questionnaire i.e. ability to make images (21 ¼ lowest,., 60¼ highest) SCHOOL1 Dummy variable for School 1 (1 ¼ School 1; 0 ¼ Schools 2 & 3) SCHOOL2 Dummy variable for School 2 (1 ¼ School 2; 0 ¼ Schools 1 & 3) SCHOOL3 Dummy variable for School 3 (1 ¼ School 3; 0 ¼ Schools 1 & 2) For parsimony, W gj in Eq. (1) represents the control for several relevant level-2 variables (W 1j þ W 2j þ . þ W gj ) that describe the student characteristics, treatment and school attended by the student. Thus, W gj represents a combination of any of the nine level-2 variables listed in Table 2. The ‘u’ is the error term The first step in the multilevel analyses was to run the so-called ‘null model’ in order to estimate the amounts of variance available to be explained at each level of the hierarchy (Raudenbush & Bryk, 2002). A null model contained only the dependent variable (FWR or BWR) and no predictor variables were specified at any level. The second step was to build up the Level-1 model, that is, the within-student model. This involved adding level-1 predictors to the model, but without entering predictors at the second level. An approach referred to as a ‘step-up’ approach was followed to examine which of the level-1 variables (listed in Table 2 above) had a significant influence on FWR or BWR in each of the hypothesized models. Bryk and Raudenbush (1992) have recommended the step-up approach for inclusion of variables into the model to the alternative approach referred as ‘working-backward’ where all the possible predictors are included in the model and then the non-significant variables are progressively eliminated from the model. The final step in the multilevel analyses involved building up the model to the second level through adding the significant level-2 predictor variables into the model using the step-up strategy. The final model for FWR at levels 1 and 2 was Level-1 model ½FWRŠ ij ¼ b 0j þ b 1j ðOCCASIONÞ 1ij þ b 2j ðLEARNINGÞ 2ij þ r ij Level-2 model b 0j ¼ g 00 þ g 01 ðYRLEVELÞ 01j þ g 02 ðTREATMNTÞ 02j þ g 03 ðAMIÞ 03j þ u 0j b 1j ¼ g 10 þ g 11 ðSCHOOL2Þ 11j þ u 1j b 2j ¼ g 20 þ u 2j The final model for BWR at Levels 1 and 2 was Level-1 model ð2Þ ½BWRŠ ij ¼ b 0j þ b 1j ðOCCASIONÞ 1ij þ b 2j ðLEARNINGÞ 2ij þ r ij Level-2 model b 0j ¼ g 00 þ g 01 ðYRLEVELÞ 01j þ g 02 ðTREATMNTÞ 02j þ g 03 ðAMIÞ 03j þ u 0j b 1j ¼ g 10 þ g 11 ðTREATMNTÞ 11j þ g 12 ðSCHOOL2Þ 12j þ u 1j b 2j ¼ g 20 þ u 2j ð3Þ
366 M. Wyra et al. / Learning and Instruction 17 (2007) 360e371 There are two issues worth noting regarding the analyses described above. First, the level-1 predictor variables (OCCASION and LEARNING) were grand-mean-centred in the HLM analyses, so that the intercept term would represent the average score for the students. Second, for both FWR and BWR, the regression coefficient of level-1 variables were left to vary across occasions because their reliability estimates were above the 0.05 value recommended by Raudenbush and Bryk (2002, p. 125) based on their extensive experience. 3. Results Descriptive statistics for each group across the five testing occasions are shown in Table 3. The pattern of recall performance is similar for both groups in both recall directions. After Test 2 there is a small decline followed by a leveling off or recovery. There is, however, a noticeable difference in the level of recall between the two groups. At Test 5 for forward recall the retrieval group recalled about 70% of the meanings of the 11 target words, while the level for the standard group was about 50%. For backward recall the corresponding figures were about 40% and 19%. Estimates of fixed effects from the two-level models for FWR and BWR have been given in Table 4 for null, Level- 1 and final models. The descriptive statistics of the variables included in the final models have been given at the bottom of Table 4. The results of the final estimation of variance components for the final FWR and BWR models and the results of the analyses of the variance components obtained from the corresponding null models are presented in Table 4, in rows ‘a’ and ‘b’, respectively. From the information in Table 4 rows ‘a’ and ‘b’, the information presented in rows ‘c’ to ‘f’ were calculated. A discussion of the calculations involved here is to be found in Raudenbush and Bryk (2002, pp. 69e95). The results in Tables 4 and 5 are discussed next in two sub-sections. 3.1. Fixed effects For the null model, the results in Tables 4 and 5 show that the predicted mean FWR score for the students is 6.16 with a variance of 10.47. In forward recall, most students were expected to remember between about three and nine words. The corresponding expectation for backward recall was between one and five words. Thus, students were much better in forward recall than in backward recall, which is consistent with expectation and findings from other studies (Ellis & Beaton, 1993). For the level-1 and final model, the results in Table 4 show that both forward and backward recall were positively influenced by occasion of testing (OCCASION) and learning (LEARNING). For example, based on the level-1 model, the results in Table 4 show that, on average, recall increased at a rate of 0.56 and 0.49 words per occasion for FWR and BWR, respectively. In addition, the results indicate that recall was significantly better immediately after learning regardless of the direction of recall. On average, for the occasion immediately after learning, recall was better by 1.11 and 1.65 words for FWR and BWR, respectively, compared to recall at the non-learning occasions. In addition, for both FWR and BWR final models, the results in Table 4 show that recall was significantly influenced by Year level (YRLEVEL), treatment (TREATMNT) and ability to make images (AMI). On average, Year 7 students outperformed Year 6 students by 1.56 and 0.89 words for forward and backward recall, respectively, while the experimental group outperformed the control group by 1.68 and 1.83 words for forward and backward recall, respectively. The significant effect of treatment indicated that there was a substantial benefit associated with the retrieval training. The impact of the treatment on forward recall was to move the mean for the group from 40.7% to 56%. The Table 3 Descriptive statistics Test 1 Test 2 Test 3 Test 4 Test 5 Mean SD Mean SD Mean SD Mean SD Mean SD Forward recall score (FWR) Standard group 3.24 2.92 5.73 3.40 5.12 3.39 5.12 3.46 5.54 3.43 Retrieval group 5.80 3.17 7.31 3.61 7.69 3.36 8.06 3.59 7.92 3.64 Backward recall score (BWR) Standard group 0.76 1.23 3.12 2.25 1.79 1.90 2.00 2.11 2.11 2.03 Retrieval group 2.23 1.99 5.00 2.61 4.39 3.15 5.09 3.11 4.39 2.43
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