Simple or complex:
A Simple hypothesis: concerns the relationship between one independent and one dependent variable (bivariate study). In experimental studies the independent variable may be considered the cause, and the dependent variable may be considered as the effect.
Example: there is a negative relationship between denial and reports of anxiety among post myocardial infarction patients
A complex hypothesis:
Concerns a relationship where two or more independent variables, two or more dependent variables, or both, are examined in the same study (multivariate).
Example: there is a positive relationship between patient perception of pain control and (a) complaints of pain and (b) requests for pain medication
Note : remember that hypothesis are not required if only one variable is being examined.