Changes in occurrence of disease over very long period of time is

Long-term or secular trends The term "secular trend" implies changes in the occurrence of disease (i.e., a progressive increase or decrease) over a long period of time, generally several years or decades. Although it may have sho-term fluctuations imposed on it, a secular trend implies a consistent tendency to change in a paicular direction or a definite movement in one direction. Examples include coronary hea disease, lung cancer and diabetes which have shown a consistent upward trend in the developed countries during the past 50 years or so, followed by a decline of such diseases as tuberculosis, typhoid fever, diphtheria and polio. Ref : Park 23rd edition Pgno : 66