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msxhj

Re: sample size calculation

Dears

I am intending to conduct a study to find out which one is faster , freehand vs. laser guide device using ultrasound on a model. only information got from previous study, freehand (median=10.5; IQR=6.5–14.5), laser device 43 (33; 21–55).

please advice on sample size, and which test i should use for comparison?

Thanks
Mahajan

[Edited by msxhj on 15-01-2010 at 09:19 PM GMT]

bvhospital

Re: Re: sample size calculation

the commonest abnormality on MRI is spina bifida (90%) and its incidence is 7/1000 live births. my hypothesis is that the spina bifida is the commonest abnormality on MRI LS Spine in patients with neurogenic bladder. i have to calculate the sample size and help of the friends who know statistics, is needed.

rqayyum

Re: Re: Re: sample size calculation

Here is an article that discusses calculating sample size for a proportion. It may answer some of your questions.
http://www.stat.auckland.ac.nz/~wild/ChanceEnc/Ch08.psampsize.pdf

rqayyum

Re: sample size calculation

I really don't think that you understood what I am asking. Anyway, enlist all abnormalities that you will be looking at and their expected proportions.... if that is too much, write one primary abnormality on MRI that you will be looking at and the expected proportion in the population under study. Give me your sample size. write down your hypothesis and null hypothesis.

bvhospital

Re: Re: sample size calculation

we want to find the MRI changes in spinal cord and lumbosacral vertebra. it will also give us the causes of neurogenic bladder in this population. kindly guide