William A. Thorpe was killed in an accident in 1918, his business continuing to operate on the island to the present day. In 1920 the Norwegian ship Spangereid caught fire and sank at her mooring at James Bay, depositing quantities of coal on the beach below the wharf. A census in 1921 showed the islands population was 3,747. The first islanders left to work at Ascension Island in 1921, which was made a dependency of St Helena in 1922. Thomas R. Bruce (postmaster 1898–1928) was the first islander to design a postage stamp, the 1922–1937 George V ship-design—this significantly contributed to island revenues for several years. South African coinage became legal tender in 1923, reflecting the high level of trade with that country. There were nine deaths from whooping cough between 1920 and 1929 and 2,200 cases of measles in 1932. The first car, an Austin 7, was imported into the island in 1929. A census in 1931 showed a population of 3,995 (and a goat population of nearly 1,500). Cable & Wireless plc absorbed the Eastern Telegraph Company in 1934. Tristan da Cunha was made a dependency of St Helena in 1938.

Based on the above article, answer a question. How many years was the time span where there were nine deaths from the whooping cough?
9
William A. Thorpe omkom i en olycka 1918, hans verksamhet fortsatte att verka på ön än i dag. 1920 fattade det norska fartyget Spangereid eld och sjönk vid sin förtöjning vid James Bay, varvid mängder kol deponerades på stranden nedanför kajen. En folkräkning 1921 visade att ögruppens invånarantal var 3 747. De första öborna lämnade för att arbeta på Ascension Island 1921, vilket gjordes till ett beroende av St Helena 1922. Thomas R. Bruce (postmästare 1898–1928) var den första ön som formgav ett frimärke, 1922–1937 George V:s fartygsdesign – detta bidrog i betydande grad till öns intäkter under flera år. Sydafrikanska mynt blev lagliga betalningsmedel 1923, vilket återspeglade den höga handelsnivån med det landet. Det inträffade nio dödsfall på grund av kikhosta mellan 1920 och 1929 och 2 200 fall av mässling 1932. Den första bilen, en Austin 7, importerades till ön 1929. En folkräkning 1931 visade en befolkning på 3 995 (och en getpopulation på närmare 1 500). Cable & Wireless plc absorberade Eastern Telegraph Company 1934. Tristan da Cunha gjordes 1938 till ett beroende av Sankta Helena. Besvara en fråga på grundval av ovanstående artikel. Hur många år var den tidsperiod då nio dödsfall inträffade på grund av kikhostan?
William A. Thorpe died in an accident in 1918, his activities continued to operate on the island to this day. In 1920, the Norwegian ship Spangereid caught fire and sank at its mooring at James Bay, with amounts of coal deposited on the shore below the quay. A 1921 census showed that the island group's population was 3,747. The first islanders left to work on Ascension Island in 1921, which was made an addiction to St Helena in 1922. Thomas R. Bruce (postmaster 1898–1928) was the first island to design a stamp, 1922–1937 George V's ship design – this contributed significantly to the island's revenue for several years. South African coins became legal tender in 1923, reflecting the high level of trade with that country. There were nine deaths due to pertussis between 1920 and 1929 and 2,200 cases of measles in 1932. The first car, an Austin 7, was imported to the island in 1929. A 1931 census showed a population of 3,995 (and a goat population of nearly 1,500). Cable & Wireless plc absorbed the Eastern Telegraph Company in 1934. Tristan da Cunha was made an addiction to Saint Helena in 1938. Answer a question on the basis of the above article. How many years was the time period when nine deaths occurred due to the pertussis?
9
9