As of September 2017, the Office for National Statistics estimated that there are over 900,000 workers on zero-hours contracts (2.9% of the employed workforce), up from 747,000 the previous year, with over 1.8m such contracts (as some people may have more than one contract), with a further 1.3m where no hours were worked. Some commentators have observed that the number of such contracts may be under-reported, as many people may be confusing them with casual employment, and may not be reporting them as temporary. The Chartered Institute of Personnel and Development (CIPD), based on a poll of 1,000 workers, reported in August 2013 that as many as 1 million workers in the United Kingdom, 3–4% of the workforce, work under the terms of a zero-hour contract. Based on a survey of 5,000 of its members Unite, Britain's largest labour union, estimates that as many as 5.5 million workers are subject to zero-hour contracts, 22% of those employed privately. The survey, conducted by Mass 1, showed that zero-hour contracts were more prevalent in northwest England, among young workers, and in agricultural work. Often workers said that holiday pay was denied (which is illegal) and in most cases sick pay. The National Farmers Union, which represents farmers, supports zero-hour contracts as offering needed flexibility for tasks such as harvesting.