

   TThhee JJaannkkaa hhaarrddnneessss ddaattaa

   DDeessccrriippttiioonn::

        Janka hardness is an important structural property of
        Australian timbers, but is difficult to measure
        directly. It is, however, directly related to the den-
        sity of the timber which is relatively easy to measure.
        In an effort to develop a method of predicting Janka
        hardness from density, the Janka hardness (here consid-
        ered the response) and the density of 36 Australian
        eucalypt hardwoods was measured.

   DDeettaaiillss::

        The data frame `janka' has two components: `dens' is
        the timber density for the tree and `hard' is the cor-
        responding Janka hardness.

        A low-degree polynomial regression may be an appropri-
        ate model. A log or square-root transformation of hard-
        ness may also be useful.

   CCAATTEEGGOORRYY::

        Polynomial regression.  Transformations.

   SSoouurrccee::

        E. J. Williams, Regression Analysis, Wiley, 1959

