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Asia-Pacific Forum
on Science Learning and Teaching, Volume 10, Issue 2, Article 5 (Dec., 2009) |
The descriptive measures of the tests for the experimental groups and the control group are given in Table 3. It is seen that students’ mean scores of pre-CAT were similar in the experimental and control groups. A one-way analysis of variance (ANOVA) was used to determine whether statistically significant differences existed among the mean scores of EG1, EG2 and CG for the results of the pre-CAT at the 0.05 level. The findings showed that there were no differences among the groups with respect to the students’ initial understandings of the concepts of acids and bases (F(2;73)=0,042; p>0.05) before the treatment. These results indicated that students in all groups were similar in respect to the initial understandings of the concepts of acids and bases before the intervention.
Table 3. Comparison of performance of experimental and control groups on pre-tests and post-tests
Note: SD: Standard Deviation; EG: Experimental group; CG: Control group
Pre-CAT
Post-CAT
Pre-Post mean difference (CAT)
Group
N
Mean
SD
Mean
SD
EG1
26
34.62
17.72
77.88
12.50
43.26
EG2
25
35.40
17.55
70.60
13.17
35.20
CG
25
36.00
16.14
60.00
15.74
24
After the treatment, the analysis of covariance (ANCOVA) was run to compare the effects of intervention on students’ understanding of acid-base concepts in post-CAT. The adjusted mean scores of EG1, EG2, and CG were 79.1, 70.1 and 58.2, respectively. Although the students in each group increased their achievement scores from pre-test to post-test, these gains were not too high. While the mean score of students in EG1 had risen from 34.62 to 77.88 with a gain score of 43.3, in EG2 it had risen from 35.40 to 70.6 with a gain score of 35.2 and in the control group it had risen from 36 to 60.2 with a gain score of 24.2 after the treatment. As seen in Table 4, the results of ANCOVA showed that the treatments resulted in significant effects on the mean scores (F(2;71)= 24,84, p<0.01). When the marginal mean scores of the groups were compared by using the Tukey test, statistically significant differences were found between the experimental groups and the control group (p<0. 01), and a remarkably significant difference was also found between the experimental groups in favor of EG1 (P<0.05). The alternative conceptions concerning the acid and base concepts were determined by the students’ responses to the multiple choice items in the CAT. Ratios of the alternative conceptions held by more than 20% of students in each group were presented in Table 5. The alternative conceptions, as reflected by the distracters in multiple-choice items, are the most common in a certain conceptual area.
Table 4. Summary of the analysis of covariance comparing the mean post-CAT scores of students in the experimental and control groups
Source of Variance
df
Mean Square
F
p
Eta-Square η2
Differences
(Tukey HSD)*Pre-CAT (cov)
1
3880.89
24.84
0.000
0.256
EG1-CG;
EG2-CG;
EG1-EG2Treatment
2
1562.69
10.00
0.000
0.217
Error
72
156.388
*significant differences among the groups according to Tukey test (at the 0.05 level)
Twenty alternative conceptions were identified and were grouped under the headings of the application of properties of acids and bases (A), pH scale (B), salts solutions (C), neutralization and titration (D), indicators (E), strength of acids and bases (F) and hydrolysis (G). While the percentages of students’ alternative conceptions in pre-test ranged from 26.29% to 80.77% in EG1, the students in EG2 ranged from 24% to 84% and those in the control group ranged from 24% to 80% (Table 5). The students in each group held almost the same alternative conceptions in the pre-test at about the same percentages. Each group showed progress in changing their alternative conceptions to the scientifically acceptable ones, but the experimental groups performed better overall. Although the experimental groups performed better, this does not mean that all alternative conceptions were remedied. The reasons for this are discussed in detail below.
