Validity is the accuracy of the information generated and it is usually measured by the standard errors of the estimates; if you are estimating a simple mean, then the formula would be S / sqrt[ sample size ].

sir namasthe and seasonal greetings

In my view validity for questionnaire

estimating error for choosing sample

i could not convenience with this formula

By  examining this formula, standard deviation is divided by sqrt of size of sample means distributing deviations among each unit of sample may give the differences or deviations between one sample to another sample. To know accuracy of questionnaire with out testing on field, without collecting samples may not be possible.

S represents for standard Deviation. Which sd?? if population sd. how to get it. it is possible only when other research suggests when they use standard tool.

with regards and respects 

rayalu K K V

Rayala, maybe then you need to formulate your question more precisely - or provide more context - so those who want to help you can give you a more specific response.

sorry if i irritated you,

my question is some formula to find  validity of a tool (questionnaire etc.,) before going to the field for investigation and to collect the data

I am not irritated  ... I am just telling you that we need more context in order to provide meaningful answers. What kind of questions? (yes/no, Likert scale, ... ?).

As a matter of fact, the concept of "validity", in a questionnaire context, often is related to whether the survey measures what it intends to measure and it comes from the way the instrument is employed. See: http://evensenwebs.com/validity.html

See: http://evensenwebs.com/validity.html