Lecture
1) The main result of action (MRA) is the experimental effect, or the effect of the action of the IV, expressed as the difference in DV values between the experimental and control conditions.
The influence of each IV, or the main result of action (MRA) of a factor, is calculated analytically or graphically as the difference in DV values between conditions that differ with respect to that factor.
Example: Moscovici, Bushini. The influence of the majority on people’s opinion + the influence of the characteristics of the message (biased/unbiased). Under the unbiased-message condition, a minority exerts a stronger influence on agreement with a decision than under the biased-message condition. This is the effect of the indirect influence of message content.
A stronger influence of the majority is exerted in the case of distorted messages.
|
Source of message /
Nature of message |
First IV |
|||
|
Second IV |
Unbiased Biased |
Minority |
Majority |
Mean |
|
0.33 0.17 |
0.19 0.25 |
0.26 0.21 |
||
|
Mean |
0.25 |
0.22 |
|
|
Analytical calculation of the MRA:
The effect of the variable «source of message» can be represented as the difference between the means taken for each of the two conditions of the second variable: 0.25-0.22=0.03
The effect of the variable «nature of message»: 0.26-0.21 =0.05
Graphical calculation of the MRA:
The X axis is the first IV (minority, majority)
The Y axis is the magnitude of the indirect influence.
The second IV consists of two lines for the biased and unbiased message (an intersecting interaction).
The MRA appears as the distance between two straight lines dropped onto the Y axis (the ordinate) – the DV indicators – from the points that are the midpoints of each of the two segments connecting the DV values for the «unbiased» and «biased» conditions. This distance (between the points 0.26 and 0.21) equals 0.05. (That is, we find the midpoints of the plots. From the midpoint of each we drop a perpendicular onto the Y axis. The distance between the projections is the MRA).
An interaction is the difference between two differences.
Gottsdanker: the experiment with monkeys.
|
Task |
Split fornix |
Intact |
|
Task 1 Task 2 |
82 62 |
83 88 |
- Analytical calculation:
88-62=26; 83-82=1; Interaction = 26-1=25
The magnitude of the interaction shows the extent to which the result of splitting the fornix depends on the tasks that were presented.
- Graphical calculation (Gottsdanker graph, p. 332)
Types of interaction.
1) Zero interaction / absence of interaction. The result segments of both groups are parallel.
(The action of the second IV has an equal-magnitude influence on the DV under all conditions of the first IV).
2) Diverging interaction (as in the case with the monkeys). (The second IV makes it possible to separate, within the DV values, the contribution of the basic variable from that of the accompanying variables.
3) Intersecting interaction. The differences in the results are equal but opposite in sign. This is the strongest interaction. Example: monkeys with a split fornix might not only solve recognition tasks worse than monkeys with a normal fornix, but also solve association tasks better.
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