A ratio of 1 shows 100 per cent reliability (no difference between test and retest) and any deviation from it indicates less reliability – the less the value of this ratio, the less the reliability of the instrument. Expressed in another way, zero difference between the test and retest scores is an indication of 100 per cent reliability. The greater the difference between scores or findings obtained from the two tests, the greater the unreliability of the instrument. The main advantage of the test/retest procedure is that it permits the instrument to be compared with itself, thus avoiding the sort of problems that could arise with the use of another instrument. The main disadvantage of this method is that a respondent may recall the responses that s/he gave in the first round, which in turn may affect the reliability of the instrument. Where an instrument is reactive in nature (when an instrument educates the respondent with respect to what the researcher is trying to find out) this method will not provide an accurate assessment of its reliability. One of the ways of overcoming this problem is to increase the time span between the two tests, but this may affect reliability for other reasons, such as the maturation of respondents and the impossibility of achieving conditions similar to those under which the questionnaire was first administered.