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fMRI has gained popularity in research and clinical settings. The majority of work relies on group comparisons to identify the resting-state network structure, connectivity, and differences between diverse populations. However, the reliability of fMRI has been doubted together with an increasing number of publications on individual differences and other factors affecting the resting-state fMRI. The current publication addresses the factors that are often overlooked or not accounted for when selecting the “healthy control group” as a baseline for comparison. Our results indicate that additional biological factors, such as blood pressure, level of hemoglobin, waist circumference, time of image acquisition, as well as age and sex introduce variability in the group data. It is therefore likely to conclude that this variability on a group level might in turn affect the differences or changes observed between populations.