One thing that trips up a lot of students up is the 85/15 rule. Basically, this means that 85% of the studies you cite in your paper must have been published within five years of the year you anticipate to graduate. For example, if you intend to graduate in 2016, at least 85% of your references should be published 2012 or later (so you could include studies from 2012, 2013, 2014, 2015, and 2016). It can be a challenge to keep your references this recent, especially if you have a topic with little emerging research or if you need to discuss a lot of older, seminal works to develop your theoretical framework or background. Some schools will allow a little wiggle room when it comes to this, but the onus is on you to figure out exactly what the expectations are from the start. The last thing you want to do is write a 50 page literature review, and then have your chair kick it back because half of your references are too dated.
One way to improve the ratio of new references to dated ones is to double or triple up on citations to back up your statements. For instance, if there are a few recent studies that support a particular statement, opt to include them all instead of only citing one. You may end up with a significantly longer list of references, but your school will be happy with you. The key is to understand the requirements before you begin doing research. I find that it’s helpful to use search filters when I’m conducting research, in order to limit results to the specific date range I need. It’s heartbreaking when you come across a study that would be PERFECT to include in your proposal… but then realize it’s 20 years old.
Okay, maybe heartbreaking is a little dramatic, but you get my point.
If you have any questions about the 85/15 rule, or anything else dissertation-related, feel free to send me an email at firstname.lastname@example.org.