د/ايمان زغلول قاسم

استاذ تكنولوجيا التعليم المشارك بكلية التربية بالزلفي

book B52

4.2.3 Coding Procedures
The coding form (Appendix 4A) was based on a method proposed by Lipsey and
Wilson (2001) and by thoroughly scanning the literature on this topic. The form was
evaluated multiple times in repetitive cycles in consultation with the coders and specialists on
this topic. The form contains multiple sections, such as study descriptors, sample descriptors,
methods and procedures (including study quality), and effect size information.
Effects of Feedback in a Computer-Based Learning Environment on Students‘ Learning Outcomes: A
Meta-analysis
73
Coding was conducted by four researchers independently. The first author coded all
studies, and 40% of the studies and 31% of all effect sizes were double-coded by one different
coder. The agreement rate between the coders was .81 for all studies and .81 for all effect
sizes. In some studies, multiple experimental conditions existed in which participants received
the same type of feedback under different conditions. For example, a study compared the
effects of KCR under program-control conditions and learner-control conditions (Corbalan,
Kester, & Van Merriënboer, 2009). In this study, mean scores of groups that received the
same type of feedback under different conditions that were not relevant to the present metaanalysis
were combined, using their weighted means and pooled standard deviations.
4.2.4 Statistical Methods
Meta-analysis is a method that enables the combination and summary of quantitative
information from different studies focusing on the same research question. Using information
from several studies gives the opportunity to provide a structured summary of a specific
research topic and to find relationships between variables that otherwise would not be
detected. A central step in meta-analysis is to make the data from each separate study
comparable. This can be done by using an effect size measure. Effect sizes express the
effectiveness of the variable of interest found in each study between a treatment and control
group in terms of standard deviation units (Lipsey & Wilson, 2001). The experimental and
control groups in each study always took the same post-test. Usually, estimates of effect sizes
obtain a plus sign if the treatment is better than the control group and vice versa (Rosenthal,
1994). We used the standardized mean differences (see Equation 1) effect size statistic.
(1)
This statistic uses the contrast between the treatment and control group divided by the
pooled standard deviation (see Equation 2).
(2)
Hedges (1981) showed that effect sizes calculated for studies with small samples
might be biased. An unbiased alternative estimator developed by Hedges (1981) (see Equation
3) was used to correct for this bias.

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