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For you a study must have how many subjects to be valid?

I understand that this question will depend on the study design.

For exemple a study who analyse the plantar pressure of 10subjects 4observer and only one measurements per subject. A total of 40measurements. Can this study be valid?

Thanks for your help

regards

 

Depends....

Validity really refers to whether a particular study is able to answer the research question(s) it is intended to answer.

In your eg it, will depend on what exactly the research question is and if the reliability of the tool doing the measurement.

 

Defalbaire,

You may want to read around the subject of statistical power. There are also plenty of free power analysis calculators available on-line.

IG

 

THANK YOU! I'm doing a study with 5 triathletes and whant to see the impact of two pairs of orthoses (1 neutral position 1 50%more correction) on the lower limb alignement and on the muscles activity while cycling. using dartfish and EMG.

Orthoses are made with cad-cam.

I was suppose to do my study on 15triathletes but for a budget and time question we will take only 5subjects and I was thinking of the validity of a study with only 5subjects.

 

It not really an issue of "validity" based on the true definition of validity. Its more an issue of generalisability of the results. With the sample size you have, then how generalisable will the results be to the population of triathletes? As Ian says, it really an issue of statistical power and sample size calculation.