How can a business measure and monitor the effectiveness of the ISMS?

I would like to ask you the following question question pertaining to ISO 27001 ISMS.....
How can a business measure & monitor the effectiveness of the the ISMS?
 

Answer:

Generally you need to to define what needs to be monitored/measured, which methods may be use, when monitoring/measurement must be done, when monitoring/measurement results must be analyzed and evaluated, who must analyze and evaluate monitoring/measurement results, etc.
For more information, this article can be interesting for you “How to perform monitoring and measurement in ISO 27001” : https://advisera.com/27001academy/blog/2015/06/08/how-to-perform-monitoring-and-measurement-in-iso-27001/ 
This free webinar can be also interesting “ISO 27001 and ISO 27004: How to measure the effectiveness of information security?” : https://advisera.com/27001academy/webinar/iso-27001-iso-27004-measure-effectiveness-information-security-free-webinar/