<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>: Ans. is d i.e., Consistent change in a paicular direction over a period of time The term Secular trend implies changes in the occurrence of disease i.e. a progressive increase or decrease in incidence over a long period of time, such as several years or decades. 