Adherence to (compliance with) drug treatment is important. However, only about half the people who leave a doctor's office with a prescription take the drug as directed. Among the many reasons people give for not adhering to drug treatment, forgetfulness is the most common.
Definition of periodical. 1  1 : periodic 1. 2  2a : published with a fixed interval between the issues or numbersb : published in, characteristic of, or connected with a periodical.
Volume typically refers to the number of years the publication has been circulated, and Issue refers to how many times that periodical has been published during that year. For example, the April 2011 publication of a monthly magazine first published in 2002 would be listed as, Volume 9, Issue 4..