When people receive their pay cheques, they may well make a comparison with earnings in the previous period. Are they earning the same, more, or less than last month or last year? There are many reasons why earnings may change. Earnings may have gone up without

any change in the work done as a result of rising money wages. Varia­ tions in earnings may be of a short term nature. Pay may vary from month to month because of seasonal factors. Earnings may be up in December because of a Christmas bonus, or down in August because holiday pay does not include a piece-rate bonus. Overtime may have been more or less in a given month, or there may have been short-time working. Variations may be more permanent. A person may have lost his job and had to find another. Another may have been promoted, moving up a career ladder. A third may have moved to a better-paying job with another employer. Particularly in the early years in the labour force, people may move from one job to another before they find the one to which they are best suited.