BUSINESS CYCLE
There are several ways to measure "the business cycle". In general, it is defined as fluctuations in the level of economic activity around an estimate of its underlying trend. Starting from a position where the level of activity is close to the trend level, a business cycle is said to be complete when the level of activity has returned back to the trend following a period when it was above, then below, the trend level, or vice-versa.
NON-SAMPLING ERROR
An error in sample estimates which cannot be attributed to sampling fluctuations (see Sampling Error). Such errors may arise from many different sources such as non-response, defects in the frame, faulty demarcation of sample units, defects in the selection of sample units, mistakes in the collection of data due to misunderstandings, to negligence or dishonesty on the part of the investigator or of the interviewee, mistakes in editing or processing the data, etc.
QUALITATIVE DATA
The data collected in business tendency and consumer opinion surveys are termed "qualitative" because respondents are required to assign qualities to the items of interest. For example, they may be asked to say whether their order books are "higher", "lower" or "same" compared with some previous period. The qualitative data obtained in business tendency and consumer opinion surveys are also described as "categorical" because respondents are required to choose between two or more response categories, such as "better", "same", "worse".
UNBIASED SAMPLE
A sample drawn by a method which is free from bias. This implies not only freedom from bias in the method of selection, e.g. random sampling, but freedom from any bias of procedure, e.g. wrong definition, non-response, design of questions, interviewer bias, etc.