title: The hidden effect of time.
abstract: It is customary to regard datasets as homogeneous with respect to the order of collection of the measurements. Examples are given in which this assumption is breached. Hidden time trends have implications for the design of studies, their analysis and interpretation. It is suggested that, if the order of observations is known, a plot by time should be performed, perhaps using a cusum.
mesh_terms: D000368:Aged; D001379:Azathioprine / Q000627:therapeutic use; D001663:Bilirubin / Q000097:blood; D001795:Blood Pressure Determination / Q000379:methods; D002940:Circadian Rhythm; D002986:Clinical Trials as Topic / Q000379:methods; D003404:Creatinine / Q000378:metabolism; D004077:Digoxin / Q000008:administration & dosage; D006801:Humans; D008105:Liver Cirrhosis, Biliary / Q000188:drug therapy; D008657:Metabolic Clearance Rate; D012107:Research Design; D012621:Seasons; D013223:Statistics as Topic; D013995:Time; D013997:Time Factors
chemical_list: D004077:Digoxin; D003404:Creatinine; D001379:Azathioprine; D001663:Bilirubin