Shashi Balain and Paul Sparrow in their report talk about Employee Engagement from all perspectives, they state it can be a fuzzy concept however it continues to grip the interests of all. This report is from 2011 so not the most up to date however the key themes are still prevalent today.
They state Employee Engagement as the notion that leads to higher performance, either at the unit level or for some theorists, even at the organisational level. This paper presents a systematic review on the topic and takes a critical look at the various perspectives on engagement..
There are few empirical papers that test employee engagement under some form of controlled conditions. Most studies have used the construct of employee or work engagement as an individual level construct, with 18 studies using it this way in contrast to only 3 studies that use it as a group level measure, despite the fact that most HR strategies use engagement as a potential predictor of collective performance outcomes. They found evidence of construct validity within existing measures, but not between them.
They conclude it is a term is to be used in a more meaningful way, we need to have a clearer definition of the construct and a shift in measurement towards both a collective level, and towards an understanding of the performance beliefs that employees are being asked to engage with. It might be better to treat employee engagement as a diffuse collective attitude of employees to their work and workplace and it might be a better strategy to device bespoke tools to measure such a collective employee attitude specific to a given organisation and the business context.
This paper makes an interesting read for those involved with setting the people strategy of businesses. The full report is available to download here.