According to widespread opinion, there is a fundamental distinction between "observed facts" on the one hand - which are the unquestionable rock bottom of science and should be collected in the greatest possible number and printed in scientific journals - and "mere theory" on the other hand, which is the product of speculation and more or less suspect.  I think the first point I should emphasize is that such antithesis does not exist.  As a mater of fact when you take supposedly simple data in our field - say determination of Qo₂ basal metabolic rates of temperature coefficients - it would take hours to unravel the enormous amount of theoretical presuppositions which are necessary to form these concepts, to arrange suitable experimental designs, to create machines doing the job - and this all is implied in your supposedly raw data of observation.  If you have obtained a series of such values, the most "empirical" thing you can do is to present them in a table of mean values and standard deviations.  This presupposes the model of a binomial distribution - and with this, the whole theory of probability, a profound and to a large extent unsolved problem of mathematics, philosophy and even metaphysics.  If you are lucky, your data can be plotted in a simple fashion, obtaining the graph of a straight line.  But considering the unconceivable complexity of processes even in a simple cell, it is little short of a miracle that the simplest possible model - namely, a linear equation between two variables - actually applies in quite a number of cases.
Thus even supposedly unadulterated facts of observation already are interfused with all sots of conceptual pictures, model concepts, theories or whatever expression you choose.  The choice is not whether to remain in the field of data or to theorize; the choice is only between models that are more or less abstract, generalized, near or more remote from direct observation, more or less suitable to represent observed phenomena.  (von Bertalanffy 1968:^ref 155-6)