Measurement:

The third method of data collection is measurement where  standardized instruments are used  to measure variables. For example, scientific instruments such as  thermometer, barometer, weighing scale are instruments for physical measures of temperature, pressure and weight respectively. Precision measure depends on  refinement of the instrument. A standard  instrument should be  used  and preferably:  the same instrument should be  used:  it is for measuring all subjects.  

What  is  the difference between "measurement" and "assessment"?  These  two terms  are sometimes used synonymously. But  there  is a difference between the two.  In  a simple way  it can be  said that measurement means to ascertain the dimensions, quantity or capacity of  objects or events, whereas assessment can be  defined as a systematic procedure of  collecting quantitative as well  as qualitative data to describe behaviour or characteristics. For example 8  rating scale to  survey job satisfaction of nurses or survey  learning needs  of nurses qualifies as assessment where  as a knowledge test on AIDS  is used to measure knowledge of AIDS  in  students. 

In measurement, numeral are assigned to objects or events according to rule to give a quantitative meaning. A numeral  is  a symbol of the form  1, 2, 3  and  so on  or I, II, III  and so on. When  quantitative meaning  is  given to  the numerals, these become numbers. Hence, number  is  a numeral  that has been  given a quantitative meaning.  It  is  easy to understand measurements used  in  natural sciences, which measure,  length, weight  and volume. Accurate scales are available for these. Measurements used  in psychological, sociological, educational characteristics or nursing care standards are difficult to  understand unless  assignment of numerals to objects or events are made according to some accepted rules  set up  on  rational or  theoretical basis. For  these measurements scales are prepared, like aptitude scale, nursing standard scale, etc.