# Screening interval 3 years and 5 years

Hello!

Have created markov model for annual screening of population with life time horizon using different screening strategies Vs no screening and annual transition probabilities for each stage of the disease. Have used currentage=start_age+_stage in the model, stages=70 since its life time horizon and starting age as 35 years for age group 35-40 years, 40 years for age group 40-45 years, 45 years for age group 45-50 years etc.

Now would like to do analysis for screening interval 3 years and 5 years with life time horizon instead of annual screening. Kindly guide how to do this.

Thanks!

1 comment
• One option would be to create a table with the ages at which screening should occur. Tables can have multiple value columns, so you could use age as the index column, then use value columns 1, 2, 3, etc. for each of your screening strategies.

Set the value column for that strategy to 1 if you want that strategy to do screening at that age. So, for example, let's say you had 4 strategies and you wanted only strategies 1 and 3 to screen at age 35. Then at age 36, only strategy 1 has screening. Then those rows of the table ScreenAgeTable would look like this.

35, 1, 0, 1, 0
36, 1, 0, 0, 0

Then, you can use a logic node instead of a chance node at the point in the transition subtree where you decide whether to do screening or not. At the screening node, enter this logical expression...

ScreenAgeTable[currentage; _strategy]

The expression above will only return 1 (true) when your table indicates that this strategy indicates screening at that age.

Note that the _strategy keyword returns 1, 2, 3 counting from the top strategy down.