<prompt> Which of the following is true about secular trend-Road side accident is a good exampleDue to environmental factorsIs due to normally occuring variation in herd immunityConsistent change in a paicular direction over a period of time  <response>: The term secular trend implies changes in the occurrence of disease i.e. Progressive increase or decreaseover a long period generally several years or decades refer page no:66 park 23 rd edition. 