SPSS中的variable measurement level(摘自spss協助文檔)

 

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You can specify the level of measurement as scale (numeric data on an interval or ratio scale), ordinal, or nominal. Nominal and ordinal data can be either string (alphanumeric) or numeric.

• Nominal. A variable can be treated as nominal when its values represent categories with no intrinsic ranking; for example, the department of the company in which an employee works. Examples of nominal variables include region, zip code, or religious affiliation.
• Ordinal. A variable can be treated as ordinal when its values represent categories with some intrinsic ranking; for example, levels of service satisfaction from highly dissatisfied to highly satisfied. Examples of ordinal variables include attitude scores representing degree of satisfaction or confidence and preference rating scores.
• Scale. A variable can be treated as scale when its values represent ordered categories with a meaningful metric, so that distance comparisons between values are appropriate. Examples of scale variables include age in years and income in thousands of dollars.

Note: For ordinal string variables, the alphabetic order of string values is assumed to reflect the true order of the categories. For example, for a string variable with the values of low, medium, high, the order of the categories is interpreted as high, low, medium--which is not the correct order. In general, it is more reliable to use numeric codes to represent ordinal data.

For new variables created during a session, data read from external file formats, and SPSS data files that were created prior to version 8, default assignment of measurement level is based on the following rules:

• Numeric variables with fewer than 24 unique values and string variables are set to nominal.
• Numeric variables with 24 or more unique values are set to scale.

You can change the scale/nominal cutoff value for numeric variables in the Options dialog box. See Interactive Chart Options for more information.

The Define Variable Properties dialog box, available from the Data menu, can help you assign the correct measurement level. See Assigning the Measurement Level for more information.