Persuasive Communication - How Audiences Decide. 2nd Edition

238 Understanding Intuitive Decision Making

Audiences can also avoid many of the diffi culties of information integration if they simply

choose the alternative that is supported by the most arguments. The more arguments that are pre-

sented for a position the more likely the audience will be persuaded to adopt it.^367 For example,

increasing the number of arguments supporting the guilt of a defendant signifi cantly increases

mock jurors’ tendency to render guilty verdicts.^368 Likewise, increasing the number of not-guilty

arguments increases jurors’ tendency to judge the defendant innocent. Moreover, mock jurors are

more likely to be persuaded by the number of supporting arguments made during jury delibera-

tions than by the number of jurors who initially support a verdict.^369

When audiences make no concerted effort to evaluate the quality of the arguments presented or

lack the expertise to do so, they are even likely to judge a large number of irrelevant arguments to

be more persuasive than a smaller number of highly relevant ones.^370 Perhaps this tendency explains

why merit raise decisions made by university committees can be predicted by simply counting the

number of activities faculty members list in their annual reports.^371

The Common Dimension Effect: The Impact of Direct Comparisons

Audiences fi nd comparing alternatives that have slot values for the same attributes (i.e., for the

same decision criteria or dimensions) easier than comparing alternatives that have unique attributes

or missing slot values. For this reason, the audience will often eliminate alternatives with unique

attributes or missing slot values from consideration or else weight those attributes less heavily, a

tendency called the common dimension effect.^372

When the audience is given the slot value of each attribute or decision criterion for all of the

alternatives under consideration, it only needs to know the relative utility of each attribute. For

example, when the audience is told that one computer has 16GB SDRAM (a type of random

access memory) and another has 8GB SDRAM, it can see that the fi rst computer has a higher

value for the attribute of SD RAM than the second, even if it does not know the meaning of

SD RAM. But if the audience is not given the values for some attributes or criteria, it needs to

know the absolute level of utility of each attribute. Thus, if the audience knows only that one

computer has 16GB SDRAM, then it must know the absolute worth of that value in order to

evaluate it.^373

Because of the diffi culties involved in calculating a value’s absolute worth, if the audience

fi nds some alternatives are missing values for some attributes, they will tend to weight those

attributes less heavily.^374 In a study illustrating this effect, judges were asked to evaluate the

grade point averages of two students, each of whom was described by two test scores. One of

the test scores came from a test both students took and the other came from a test only one of

the students took. Judges systematically gave more weight to the scores from the test taken by

both students.^375

Audiences are susceptible to the common dimension effect even when information is presented

to them in paragraph form as opposed to tabular or matrix form. Paragraph form makes fi nding the

common attributes or decision criteria of alternatives more diffi cult than a matrix format. In a study

of the common dimension effect in paragraphs, readers were presented with pairs of paragraph that

described videogames and asked to choose the game they thought would sell best and to justify their

decision. Each pair of games had two attributes in common and two unique attributes. Despite the

diffi culties caused by the paragraph format, readers still tended to ignore the slot values of the unique

attributes and to make and justify their decisions based on the different slot values each game had on

the two common attributes.^376

In a follow-up study, college students were shown descriptions of colleges written in para-

graph form. The students were asked to think aloud as they decided which college they would