Hi there,
first of all, there are so many ways of conducting performance appraisals. A good start would be to check out what different kind of performance management strategies are used in hospitals and which ones seem to work better then others and why. Look at employee engagement, turnover of staff, etc. If the essay is geared around performance appraisals in general, maybe a paragraph could be said on the traditional approach vs the continuous feedback model?! There are plenty of articles and blogs on the net. Long employee performance appraisal questionnaires are only one solution and a heavy criticized one too, so be open and read a lot! Enjoy the research, it is a great topic. Good luck! :-)