With almost 80% of the total land area suitable for crop production and about 17% of the labor force engaged in farming, agriculture remains the primary occupation, accounting for 11% of GDP in 2001. Value of agricultural output grew at an average annual rate of 7.1% during 1968–73, but since 1975 the sector has been hampered by droughts (1975, 1977, and 1979), hurricanes (in 1979 and 1980), and slumping world prices and quota allocations for sugar (since 1985). In 1999, agricultural production was 0.4% higher than during 1989–91. The fertile Cibao Valley is the main agricultural center. In 1998, arable land totaled ; with land under permanent crops at .
Question: Agricultural production was 0.4% higher than how many years?
Answer: 2