<P> Concepts in Hempel's deductive - nomological model play a key role in the development and testing of hypotheses . Most formal hypotheses connect concepts by specifying the expected relationships between propositions . When a set of hypotheses are grouped together they become a type of conceptual framework . When a conceptual framework is complex and incorporates causality or explanation it is generally referred to as a theory . According to noted philosopher of science Carl Gustav Hempel "An adequate empirical interpretation turns a theoretical system into a testable theory: The hypothesis whose constituent terms have been interpreted become capable of test by reference to observable phenomena . Frequently the interpreted hypothesis will be derivative hypotheses of the theory; but their confirmation or disconfirmation by empirical data will then immediately strengthen or weaken also the primitive hypotheses from which they were derived ." </P> <P> Hempel provides a useful metaphor that describes the relationship between a conceptual framework and the framework as it is observed and perhaps tested (interpreted framework). "The whole system floats, as it were, above the plane of observation and is anchored to it by rules of interpretation . These might be viewed as strings which are not part of the network but link certain points of the latter with specific places in the plane of observation . By virtue of those interpretative connections, the network can function as a scientific theory ." Hypotheses with concepts anchored in the plane of observation are ready to be tested . In "actual scientific practice the process of framing a theoretical structure and of interpreting it are not always sharply separated, since the intended interpretation usually guides the construction of the theoretician ." It is, however, "possible and indeed desirable, for the purposes of logical clarification, to separate the two steps conceptually ." </P> <P> When a possible correlation or similar relation between phenomena is investigated, such as whether a proposed remedy is effective in treating a disease, the hypothesis that a relation exists cannot be examined the same way one might examine a proposed new law of nature . In such an investigation, if the tested remedy shows no effect in a few cases, these do not necessarily falsify the hypothesis . Instead, statistical tests are used to determine how likely it is that the overall effect would be observed if the hypothesized relation does not exist . If that likelihood is sufficiently small (e.g., less than 1%), the existence of a relation may be assumed . Otherwise, any observed effect may be due to pure chance . </P> <P> In statistical hypothesis testing, two hypotheses are compared . These are called the null hypothesis and the alternative hypothesis . The null hypothesis is the hypothesis that states that there is no relation between the phenomena whose relation is under investigation, or at least not of the form given by the alternative hypothesis . The alternative hypothesis, as the name suggests, is the alternative to the null hypothesis: it states that there is some kind of relation . The alternative hypothesis may take several forms, depending on the nature of the hypothesized relation; in particular, it can be two - sided (for example: there is some effect, in a yet unknown direction) or one - sided (the direction of the hypothesized relation, positive or negative, is fixed in advance). </P>

Which of the following statements is an example of a complex hypothesis