Perfiles y modelos de Uso

Specific response forms were devised to capture receptive as well as expressive information. The same form was copied twice for each child and marked to indicate pre - test and post - test. The response forms were not analysed or scored until after all the participants had completed both the pre and post-tests so as to limit the researcher and the assistant’s knowledge of pre and post-test scores. This also decreased investigator bias as no prior knowledge of pre-test scores was available at the time of the intervention.

The raw data was then entered into a spreadsheet for easier management of data and presented to the Stellenbosch University Biostatistics Department for further analysis.

3.10.1. Statistical Analysis

The Wilcoxon Signed Rank Test was used in analysis of the data. This test is defined as a non-parametric test which compares the central tendency of two matched samples (Howell, 1999). This analysis method was chosen due to the small sample size (n = 20) as well as the fact that the samples were matched and compared both to themselves as they were pre- and

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post-tested and to each other to measure the control group (Lunenburg & Irby, 2009). This form of analysis allows one to make comparisons between groups, without making generalized assumptions about the whole population.

Parametric analysis methods assume that distribution of data is normal, where nonparametric analysis methods do not make those normalcy assumptions. The Wilcoxon Signed Rank test is useful in analysing data when the sample is not considered to be normal and representative but is evenly spread on either side of the median (Sprent & Smeeton, 2001). Another aspect of efficacy of the Wilcoxon test is that the statistical properties of the test remain the same, regardless of the data that is put into each ranking, as long as the ranking remains the same (Hettmansperger & McKean, 2011). A Wilcoxon analysis design is considered to be more resistant than a t-test insofar as nonparametric tests are concerned and are also considered to have high levels of efficiency and robustness (Hettmansperger & McKean, 2011).

These attributes are appropriate for this study as there are no assumptions made as to what the distribution of the data should be and therefore, the pre and post-test information can be analysed according to what is found, rather than what should be expected to be found (Howell, 1999). Each score is ranked according to the median. If there has been a positive effect then it is assigned a positive rank and if it is negative, it is assigned a negative rank. When the distribution of positive and negative ranks is evenly spread around the mean, then the assumption is deemed to be true (Sprent & Smeeton, 2001).

These methods are used to analyse the data and not the properties of the data (Altman & Bland, 2009). The Wilcoxon test relies on the rank order of the observations rather than on the measurements. Another advantage of non-parametric tests is that they are not affected by outliers which were observed on a few occasions in the data (Howell, 1999).

A 5% significance level (p < 0.05) was used as a guideline for determining significant effects of interventions and results were awarded a 95% confidence level rating. The absolute gains are measured as the difference between the pre and post test scores of the experimental group when compared to the pre and post-test differences of the control group and were measured in %. The percentage gains were indicated as the difference between the pre and post test scores of the individual group only and not as the difference between the two groups of participants.

79 3.10.2. Validity Measures

All tests were administered by the research assistant and the intervention process itself was carried out by the researcher. This allowed for a double blind research method to improve the validity and reliability of the study. This double blind was achieved by the research assistant testing all the children within a week, not knowing which groups the children were assigned to. This did not allow for any bias in test results. She then kept the test results until after the intervention was completed, after which the research assistant retested all the participants. This did not allow for any prompting or specific teaching of vocabulary by the researcher when providing the intervention. It also eliminated the assumption of shared knowledge when retesting the children.

Multiple test effects variables were attempted to be managed by spacing out the pre and post -

tests (Meline, 2010). The tests were administered three weeks apart with the intervention occurring in between. This short intervention period allowed for control of maturation within the subjects (Seabi, 2012) and ensured that target words were less likely to have been learned in class.

No selection bias (Seabi, 2012) affected the validity of the study as the participants meeting the selection criteria were randomly assigned to groups.

Content validity (Lunenburg & Irby, 2009) was attempted to be controlled for by rewriting

the stories to incorporate the words that were to be tested. These words appeared in the story at least three times each in order to make sure that the participants were sufficiently exposed to these words within context. Assessments also used pictures that were taken directly out of the books that were used to ensure that the children had a mental reference for the target word.