What impact did Chadwick's work have on life expectancy by the year 1900?

Chadwick's work had a profound impact on public health and ultimately contributed to an increase in life expectancy by 1900. His report in 1842 highlighted the appalling living conditions in urban areas and the link between poor sanitation and the spread of diseases. This was pivotal in prompting reforms in public health policies, including sewer systems and clean water supply initiatives.

The implementation of these reforms led to a decrease in the prevalence of infectious diseases that were previously rampant in crowded and unsanitary conditions. Consequently, improved sanitation and access to clean water were significant factors in raising overall life expectancy during this period. While it is true that the benefits of these improvements were not uniformly experienced by all social classes initially, the overall trend indicated a significant increase in life expectancy for the general population by 1900.

The other options do not reflect the positive outcomes that followed Chadwick's work—there was a marked improvement in public health conditions that did not align with decreased life expectancy or inconsistent improvements across different socioeconomic groups.