Calculating and combining P-values from multiple studies has long been used in the meta-analysis of microarray data, and we are now using these approaches for metabolomics data. These are simple to calculate and flexible to use.
Fisher’s method and Stouffer’s method are two popular approaches. They have similar levels of performance and can be easily interpreted whereby larger scores reflect greater differential abundance.
The main difference is that weights (i.e. based on sample sizes) are incorporated into the calculation in Stouffer’s method, whereas Fisher’s method is known as a weight-free method.
Note that larger sample size does not warrant larger weights, as the quality of each study can be variable. Users should choose to apply Stouffer’s method only when all studies are of similar quality.