Small relative to other sources of variation. For example, a professional footballer who is used to sea-level will still perform better at a match in La Paz tha

Small relative to other sources of variation. For example, a professional footballer who is used to sea-level will still perform better at a match in La Paz than an average joe who was born in La Paz. Similarly, Similarly, there might be minute differences between people based on birth order, but in most scenarios these would be swamped by all other factors that go to make up someone's personality. That doesn't make me politically correct, rather it makes me unmotivated to further explore the topic.