I am writing a synopsis for my dissertation on a topic in which I'm comparing 2 endodontic sealers clinically (RCT). there are no clinical studies for their comparison in literature till now. I am having difficulty in calculating sample size. I need guidance.
Sarang , just in addition to your own question can I mention the area of outcome measurement and primary and secondary outcomes.
When designing a randomised controlled trial then ensure you consult the Cochrane Handbook to familiarise yourself with goo RCT design first. This will reduce potential risk of bias.
I will discuss the area of outcome measures chosen when designing an RCT and in good design the researcher needs to decide what will be the Primary Outcome measure and what should be the secondary outcome measures. This is very important because often incorrect design lumps a lot of outcome measures together and then in hindsight the measures that show the most statistical improvement are the ones that are reported as Primary etc. If there are a lot of outcomes used then this increases the chances of a random positive finding!!!
When designing your protocol think what aspect of a patients function would a new intervention be likely to effect and call that the primary outcome and all else the secondary. There is absolutely no harm in seeing no statistically significant improvement in the primary outcome in terms of reporting. I find that this is one issue that has cropped up in our research group.
So with an intervention before beginning the RCT think what aspect of function would most likely be altered by the intervention and then find a reliable (Intra/inter rater) and valid scale for this which you call the primary outcome measure. All else will be secondary.
I have the primary outcome to measure on reliable scale with intra & inter observer reliability. But unable to find suitable sample size to defend my dissertation.
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