| http://www.w3.org/ns/prov#value | - Although they made adjustments for variables that could affect the results, such as the men's ages, the season, the centre where they gave their sperm samples, and the technique (standard in vitro fertilisation or intra-cytoplasmic sperm injection), they were unable to control for socioeconomic factors, including smoking and weight, which can affect semen quality and concentration.
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