Standard deviation of two sets from the same sample

iccf

New Member
#1
I am currently looking at some neuroimaging data from 18 subjects. However, the sample is split into left and right hemispheres, and I want to combine the measurements into one total mean and standard deviation. Furthermore, I do not have the correspondent left and right measures for each patient, just a list of all the right and left outputs:

Left hemisphere:
0.08907489 0.100528634 0.102290749 0.100748899 0.107136564 0.105374449 0.109559471 0.109339207 0.11154185 0.115506608 0.113744493 0.113744493 0.115947137 0.122555066 0.125638767 0.130044053 0.128502203 0.136211454

Right hemisphere: 0.094517766 0.101624365 0.103654822 0.104162437 0.106700508 0.111269036 0.11177665 0.10822335 0.109746193 0.110761421 0.112284264 0.115329949 0.118883249 0.124467005 0.124467005 0.127005076 0.132588832 0.137664975

The mean should be quite easy to calculate as it's just the average of the means of the two groups. However, the problem is how to calculate the standard deviation without knowing which patient the left and right measurements belong to. Is it feasible? If so, how?

Thank you!