That's right, sample size can vary a lot depending on several factors such as: * Experiment design * Sampling techniques * Methodology being used on the mode

That's right, sample size can vary a lot depending on several factors such as: * Experiment design * Sampling techniques * Methodology being used on the model But normally with a small sample size a bigger emphasis should be put on performing the appropriate statistical tests on the sample and validating it carefully, before applying any model. There are a lot of assumptions that should be validated if you are working with small data. Unfortunately, I don't have access to the complete paper to verify the methodology used, so take it all with a grain of salt.