The Nigerian passport has ranked 191 out of 199 countries, making it the 10th worst travel document worldwide, according to VisaGuide's World Passport Index.

According to the report, as of April, the Nigerian passport only emerged above countries like North Korea (192), Iraq (193), Libya (194), Sudan (195), Pakistan (196), Afghanistan (197), Syria (198) and Somalia (199).

The index is a passport ranking system that uses the Destination Significance Score (DSS) for assessing and ranking the passports of countries and territories.

The rankings are usually based on various factors to determine their strength and assign a unique value to each passport.

In the latest index, the Singaporean passport came first on the chart as the strongest in the world, followed by the Italian passport.

Based on the index, Spanish, French and German passports are ranked as third, fourth, and fifth respectively.

The report disclosed, "To reach a unique ranking, we assign a value, which we call Destination Significance Score (DSS), to each travel destination."

It added, "A unique DSS value is assigned to each destination based on the entry policy it enforces on the passport, GDP, Power Index, Tourism Index and Human Development Index (HDI), among other factors. The DSS is multiplied with the value of the visa requirement of the destination country toward the selected passport holders."

Other factors are visa-free travel, electronic travel authorisation, visa on arrival, electronic visa (e-visa), embassy or other government-approved visas, passport-free travel, and banned entry.

It also noted that since destination countries are each assigned a unique DSS, "Being able to travel visa-free to a destination with a higher DSS gives the selected passport a higher value than having visa-free access to a country with lowed (sic) DSS."

"This results in a more accurate ranking for each passport," stated the index.

It also mentioned that after all factions were calculated, each passport had its unique value, with no two countries having the same number of "visa-free" destinations.