Understanding Society User Support

Question in related to participants' response for chronic conditions: Although the same questions were asked in wave 1, 4 & 7 in the UKHLS (“Has a doctor or other health professional ever told you that you have any of the conditions listed on this card? Please just tell me the numbers that apply”), individuals’ replies to the number of diagnosed health conditions showed a great different among wave1 and waves 4&7. In wave 4 and wave 7, most individuals replied “inapplicable” to this question. Why this happened?