A well-known case for confounding was the finding of night lighting casing myopia in young children.
In 1999 Quinn et al. published an article in the prestigious journal Nature that reported a strong association between exposure to nighttime light before the age of two years and myopia and created wide publicity in the media. As axial myopia is caused by excessive eyeball growth during childhood, the researchers rationalised that nighttime lighting in young children could stimulate the condition.
However, multiple studies that repeated the investigation found no association between the exposure (night light) and the outcome (myopia).
Myopic parents
It turned out that the fault was from those myopic parents of those infants who had the habit of keeping the lights on at night for better vision and created the confounder. As myopic parents tend to have myopic children, the association now looked easier to understand.
References
Myopia and ambient lighting at night: Quinn et al.
Continuous ambient lighting and eye growth in primates: Smith et al.
Myopia and night lighting in children in Singapore: Saw et al.
