Grey literature is important for many reasons.
1. It allows you to incorporate information such as government statistics and experiments that may not have been published, such as experiments that led to negative or null results. This decreases any bias that may arise if you only chose formally published literature, which is more heavily skewed towards positive results in experiments.
2. It allows you to fully understand the full range of information on offer and come to a more reasoned conclusion as you have broadened your research beyond published material.
3. Grey literature does not have to fit into the guidelines provided by journal publishers and so is usually more detailed than journal articles in terms of the experiment or study methodology and the context surrounding a publication.
