I am sorry- I will try to explain. The data analyzed was collected in 4 periods but in each period we collected data about different patients. I would like to assess if there is a significant change in age of first diagnosis in the various periods- for example, we have data on age of diagnosis of asthma for all the new patients in a defined community in 2008 and data on age of diagnosis of asthma for all the new patients in 2012 and in 2016. Mean age at each period was different and the difference is significant. My question is how can I evaluate if there is a pattern in the change (is the mean age increasing linearly over these periods?). I hope this is more clear. Thanks again!
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