(Bloomberg) — South Africa’s biggest farm-industry lobby said a probe into the statistics agency’s methods showed that agriculture hadn’t contracted as much as reported this year and called for a reform of the calculations.

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Agri SA asked the Bureau for Food and Agricultural Policy to review Statistics South Africa’s data after the agency said the farming sector contracted 15.5% in the first nine months of the year and 28.8% in the third quarter — the most in three decades. That triggered an unexpected contraction of 0.3% in the nation’s overall quarterly economic performance relative to the prior three months.

BFAP’s analysis released Friday showed the farming industry has shrunk about 5% to 6% so far this year, and that Statistics South Africa should consider an “upward revision” of about 10.8 billion rand ($590 million) for agricultural gross domestic product after accounting for inflation. Statistics South Africa didn’t immediately respond to an emailed request for comment.

“While acknowledging the complexity and difficulty in sourcing real-time statistics to calculate the sector’s economic performance in aggregate, the report suggests that reforms are necessary to ensure more robust indicators for the agricultural economy,” AgriSA said in a statement accompanying the analysis.

Based on BFAP’s work, the economy would have grown by 0.7% so far this year rather than the 0.4% reported, the study showed.

South Africa’s economic expansion has averaged less than 1% over the past decade, outpaced by population growth. An El Niño-induced drought hurt local output of summer crops including a 23% plunge in production of corn that’s used as a staple food and as animal feed.

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