CHAPTER III
MATERIALS AND METHODS
Study Design and Search Strategies
This meta-analysis was conducted to examine STH infections in school children and its influence on their academic performance. The findings are used to propose an improved control strategy that will assist public schools in the Philippines to protect the wellbeing and health of their students. Articles were searched on databases such as PubMed/Medline, ScienceDirect and Google Scholar. Search terms and phrases in these databases include: Ascaris lumbricoides, Trichuris trichiura, hookworm, intestinal parasite, cognitive domain, cognitive function, memory, learning, absenteeism, reaction time, school children, children, academic performance, anemia, malnutrition, abdominal pain, and diarrhea. These terms were searched either separately or in combination.
Inclusion and Exclusion Criteria
Articles were initially chosen based on their titles and abstracts, followed by screening the full articles to see if they meet the specific selection criteria.
Reference lists of the chosen articles were scanned to look for other possibly eligible articles for the study.
Inclusion Criteria
Published and unpublished articles in the English language from the last forty years, covering from 1980 to 2020 were included. All observational study designs including cross-sectional, longitudinal, case control and experimental study were also considered. Studies that assessed nutritional status according to anthropometric z-score measurements and anemic status using a hematology machine were considered. Anemic status was defined as children who had hemoglobin concentrations below 115g/L (World Health Organization 2000).
Records concerning nutritional and anemic status were included if the groups compared were parasitized children and non-parasitized children.
Articles that assessed the cognitive ability of children infected with a single STH infection were considered for the study. Studies that looked into at least one cognitive domain (memory, learning, or reaction time) were considered. All aforementioned study designs were also considered for review, with experimental studies specifically being clinical trials that had a group which received an anthelmintic drug versus a group that received identical placebo.
Exclusion Criteria
Articles which were not fully accessed such as the unavailability of their full texts or no response of its author via email, articles which included soil- transmitted helminth species and cognitive domains outside of the scope of the study were excluded. Studies assessing nutritional and anemic status that did not include the frequency of children with the sequelae and control group of interest were removed. The association between T. trichiura infection and anemic status was not included in the meta-analysis due to the very little literature that exists for the parameters of interest. Articles that did not report statistical data in terms of the mean and standard deviation were excluded.
Psychometric Assessment of Cognitive Function
Studies assessing single or multiple domains in school children were conducted through several psychometric instruments (Pabalan et al. 2018). In this study, the cognitive function of children was assessed through three domains:
memory, learning, and reaction time. Tests for memory measured the domain in terms of working or short-term memory and in terms of long-term memory.
Learning tests measured the domain in terms of paired-associate learning and in the ability to learn concepts and estimate overall learning potential and intelligence.
Lastly, the reaction time domain was assessed by a test that measured reaction time in terms of speed of comprehension and verbal information processing.
Data Extraction
The following information was obtained from each article: author’s surname, year of publication, country of origin, parasites involved, age range of subjects, study design, sample size and effect outcomes. From the articles chosen for meta-analysis, the following were extracted: author’s surname, year of publication, frequency of events, mean, standard deviation and sample size of parasitized and non-parasitized children. Data was tabulated in a Microsoft Excel spreadsheet.
Risk of Bias Assessment
In accordance with the Cochrane Collaboration’s tool, the quality of included studies was assessed using Review Manager version 4.5, a data management software. The assessment covered seven aspects: selection bias (random sequence generation and allocation concealment), performance bias (binding of participants and personnel), detection bias (blinding of outcome assessment), attrition bias (incomplete outcome data), reporting bias (selective reporting) and other bias. Each article was rated low, high or unclear risk and any differences in rating were resolved by discussion and consensus by the authors.
Statistical Analysis
Analysis of data was performed through Review Manager version 4.5.
Continuous outcomes were defined as the scores from cognitive tests which assessed memory, learning, and reaction time. Dichotomous outcomes were identified according to an individual’s nutritional and anemic status. Statistical analysis of cognitive domains was reported using the T-test to compare the equality of two population means. Dichotomous outcomes were calculated and reported as an odds ratio. Forest plots were generated for each outcome to show a summary of the variations among studies (Schriger et al. 2010). Heterogeneity was determined through the I2 statistics due to its ability to effectively detect heterogeneity in an analysis involving a small number of studies, a more optimal test compared to Cochran’s Q (Higgins et al. 2003). The confidence level was set to 95% and a significance level of <0.05 was used. I2 values of 25% and below, 50% and 75%
and above were considered low, moderate, and high, respectively. A random effects model was used to provide a conservative prevalence estimate for cases of moderate to high heterogeneity while a fixed effects model was used for low heterogeneity.
Publication bias was assessed using the same software. Discrepancies regarding the studies were discussed by the authors and a resolution was done after considering the disagreements.
Figure 4. Summary flowchart of literature data collection
