Читать книгу The Tao of Statistics - Dana K. Keller - Страница 17

 The rare ruler

 The flexible measure

 Precious property

A ratio level of measurement scale has a true zero and is the trophy of data types. Weight and height are examples. We can say that half of 100 pounds is 50 pounds, and twice 6 feet is 12 feet. In other words, we can form interpretable ratios. These types of data are almost carefree in their use with regard to their level of measurement (assumptions on their distributions is another story, which will be told shortly).

The high school maintains basic health information in the nurse’s office on such things as height, weight, and inoculations, but the high school principal would likely need a good reason to be granted access to many of these data. The principal does have, however, somewhat unlimited access to absentee and tardiness information. These variables are at a ratio level of measurement. Depending on how the data are coded and used, though, they could be at any of the levels of measurement. Recoding (assigning new codes after the fact) can further complicate understanding the data’s true level of measurement. Yet the principal has no hesitation in asking his office staff to do the tedious aspects of his research for him, as they are responsible for the same types of security and attention to detail as he is.

The director of public health has electronic medical information for all Medicaid recipients in her state, although restrictions on the data’s use are quite stringent. Nonetheless, for a variety of purposes, she might have access to any of the types of information, including measures that have true zeros. For example, when looking at the degree of compliance with national adult immunization guidelines, she knows the number of different immunizations appropriate to adults and the number of immunizations delivered. Knowing who received which immunizations and counting them for each adult, she can form ratio scales for immunization counts and for rates of immunization compliance. The more her data are measured on interval and ratio scales, the larger the variety of statistical techniques that will be available.