In an article on unsafe abortions and urban poverty in Nairobi's Kibera slum, the UK's Guardian newspaper claimed nearly half of Kenya's goods and services were produced in the capital.
"Nairobi is the economic heart, accounting for 45% of the gross domestic product of a country approaching middle-income status," it said.
Is the figure correct? We checked.
GDP data now available by county
The journalist who wrote the article has not responded to our request for the source of the statistic. (Note: We will update our report if she does.)
Earlier reports put Nairobi's share of GDP at 60%. They include:
Nairobi county's 2019/20 development plan
A 2017 policy brief by the UN Development Programme
2009 research on Nairobi's slum economies by the London School of Economics
Nairobi is both a city and one of Kenya's 47 counties. Until February 2019, the Kenya National Bureau of Statistics did not publish GDP figures for counties. But its latest report, prepared with help from the World Bank, does.
Nairobi's estimated share of national GDP from 2013 to 2017 was an average of 21.7%. Second was Nakuru county at 6.1%, with Kiambu (5.5%) in third place.
Expert warns lower figure still a cause for concern
Nearly a third of Kenya's GDP comes from agriculture. Very little of this happens in the capital, said Dr Kennedy Opalo, an assistant professor at Georgetown University in the US with expertise in the political economy of development.
"A lot of non-agricultural economic activity is concentrated in Nairobi."
This wasn't unusual, as capital cities tended to contribute the most to their countries' economies, Opalo told Africa Check. "Economic concentration of this kind is often unavoidable."
But the fact that one county out of 47 contributed a fifth of GDP "should worry the government because too much concentration may result in greater inequality at all levels of the income distribution".
Conclusion: Nairobi produced an average of 21.7% of Kenya's GDP from 2013 to 2017.
The UK's Guardian newspaper claimed Nairobi produced 45% of Kenya's GDP. A February 2019 national statistics agency report, which included GDP estimates for counties, put the figure at an average of 21.7% from 2013 to 2017.
But a development expert warned that the capital's share of GDP - roughly a fifth - should still concern the government because too much economic concentration could lead to greater inequality.