ABSTRACT
We propose a method for detecting a Guttman effect in a complete disjunctive table U with Q questions. Since such an investigation is a nonsense when the Q variables are independent, we reuse a previous unpublished work about the chi-squared independence test for Burt's tables. Then, we introduce a two-steps method consisting in plugging the first singular vector from a preliminary Correspondence Analysis (CA) of U as a score x into a subsequent singly-ordered Ordinal Correspondence Analysis (OCA) of U . OCA mainly consists in completing x by a sequence of orthogonal polynomials superseding the classical factors of CA. As a consequence, in presence of a pure Guttman effect, we should in principle have that the second singular vector coincide with the polynomial of degree 2, etc. The hybrid decomposition of the Pearson chi-squared statistics (resulting from OCA) used in association with permutation tests makes possible to reveal such relationships, i.e. the presence of a Guttman effect in the structure of U , and to determine its degree - with an accuracy depending on the signal to noise ratio. The proposed method is successively tested on artificial data (more or less noisy), a well-known benchmark, and synchrotron X-ray diffraction data of soil samples.
ABSTRACT
Pancreatic and salivary isoenzymes of amylase were determined in serum from 70 subjects. Thin-layer gel/isoelectric focusing was used to separate the isoenzymes. Because other studies (J. Lab. Clin. Med. 90: 141-151, 1977) show that the major isoamylases have isoelectric points between 5.8 and 7.2, we focused the sera on polyacrylamide gel plates with a pH gradient from 5.5 to 8.5. The separated amylase fractions were made visible by direct incubation with a commercially available dye-starch polymer. Isoelectric focusing proved to be convenient, precise, and reproducible, and it can be used as a routine analysis to detect even slight changes in serum amylase distributions. We found that the isoamylase distribution is age dependent, whereas total amylase activity shows no correlation with age.
