The Higgins index indicated high heterogeneity (98.5%) among the studies concerning citric acid (96.9%) and ascorbic acid (91.4%). The study included 24 publications between 19 (mode 1998), totaling 4215 nursery piglets. This study evaluated different meta-analytical approaches tousing citric and ascorbic acids in the performance of nursery piglets. More important, to our knowledge this is the first description of a method for producing a statistically adequate but graphically appealing forest plot summarizing descriptive data, using widely available software. It is possible to conduct a meta-analysis using only Microsoft Excel. We have also developed a second spreadsheet capable of producing customized forest plots. We constructed a step-by-step guide to perform a meta-analysis in a Microsoft Excel spreadsheet, using either fixed-effect or random-effects models. Analyses can be conducted using Microsoft Excel, but there was no previous guide available. Most available softwares have limitations in dealing with descriptive data, and the graphical display of summary statistics such as incidence and prevalence is unsatisfactory. Commercial specialist software is available, but may be expensive and focused in a particular type of primary data. General purpose statistical packages can meta-analyze data, but usually require external macros or coding. Meta-analyses are necessary to synthesize data obtained from primary research, and in many situations reviews of observational studies are the only available alternative.
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