Comparative judgements and preferences: The influence of the number of response alternatives

Abstract

Following announcements of plans for a new nuclear power station in south‐west England, local residents were sent questionnaires in which they were asked to give estimates, in percentage terms, of the present, future (2000 AD) and ideal contributions to the UK electricity supply of different energy technologies. In Expt 1, 184 subjects rated five technologies (plus an ‘other’ category), and 10 months later they were split into five groups, each of which had to rate only one of the technologies previously presented. In Expt 2, three versions of the questionnaire were used, requiring ratings of ( a ) nuclear only, ( b ) nuclear, coal, plus ‘other’ and ( c ) eight technologies (including nuclear and coal) plus ‘other’. These were first completed by 220 subjects; six months later a subsample of 134 were each sent one of the two versions other than the one they had previously completed. In Expt 3, 164 subjects gave ratings, in four conditions, of ( a ) nuclear only, ( b ) coal only, ( c ) four technologies plus ‘other’ and ( d ) seven technologies plus ‘other’; the order of ratings was also changed with preferences first, present estimates second, and future predictions third. Broadly, all three experiments showed that the more technologies subjects had to rate, the smaller were the percentage ratings they gave to any single technology. These findings are considered in relation to context effects in judgement, and to the availability heuristic. Implications for interpretation of opinion poll findings are discussed.