HELP me in choosing wich statistical analysis should I use?

Hi all!

I am trying to publish a scientific paper about a posibble correlation and link between varoius blood disorders and a specific laboratory parametar. There are 7 health disorders wich I tought should be grouped in 7 groups of 30 patients (beacuse of the statistical significance). The problem is that the parametar has values that are not natural numbers. The values are decimals like 0.985 or 0.915 or 0.945 etc.

Another problem is that the values are very close to each other and I dont know any statistical analysis who can discover significant differences between two values that are so small. Vaorious patients for different groups have similar values that differ slightly. I dont know what "slightly" is for numbers that are so small.

I tought using the Mann Whitney test because it can cross examine any two individuals for two groups?? Whar are your toughts?

Please advise