Weapons and Aggression

Can the presence of a weapon or even a picture of a weapon cause people to behave more aggressively?

Anderson, C.A., Benjamin, A.J., & Bartholow, B.D. (1998). Does the gun pull the trigger? Automatic priming effects of weapon pictures and weapon names. Psychological Science, 9, 308-314.
 

Background, Experimental Design, and Materials

Web Resource: Rice Virtual Lab in Statistics By David M. Lane

Case: Weapons and Aggression

Click the above link and a new web page, Weapons and Aggression, will appear. Next, choose Background, Experimental design, and Materials from the list to the left.

Repeated-Measures Design

The hypothesis is that a person can name an aggressive word more quickly if it is preceded by a weapon word than if it word is preceded by a neutral word. (Please refer to the Experimental Design section.)

Repeated Measures Design: According to researcher, each subject named both aggressive and non-aggressive words following both weapon and non-weapon "primes." Thus, it is a repeated measures design.

Within-Subjects Factors

1. Prime type with two levels: weapon or nonweapon words

2. Target type with two levels: aggressive vs. non-aggressive words

3. Combinations of two within-subjects factors: There will be four experimental conditions. Each subject will experience every experimental condition.

 

	1. Aggressive	2. Nonaggressiive
1. Weapon	Weapon/Aggressive	Weapon/Nonagressive
2. Nonweapon	Nonweapon/Aggression	Nonweapon/Nonagression

Dependent Measures

Reaction time: The time it takes to name a target word (either an aggressive or non-aggressive word) presented on computer screen. Specifically, subjects were given 48 trials in each of the four prim x target type condition. The means were then computed. Thus, four mean reaction time scores were recorded for each subject.

Data Set

The data set includes the ID number (subno), gender (sex), the reaction time measured in the Weapon/Aggressive condition (aw), the reaction time measured in the Nonweapon/Aggression condition (an), the reaction time measured in the Weapon/Nonaggressive condition (cxew), and the reaction time measured in the Nonweapon/Nonaggressive condition (cxen).

 

Prime	Target	Reaction Times
1 Weapon	1 Aggressive	AW
	2 Nonaggressiive	CXEW
2 Nonweapon	1 Aggressive	AN
	2 Nonaggressiive	CXEN

subno sex aw an cxew cxen

1 F 44.6667 44 43.2409 45.1564

2 F 42.7083 43.7273 46.8628 45.1278

3 F 41.6957 41.8182 44.4939 43.3712

4 F 34.7778 37.1364 35.2715 34.4035

5 F 47.0833 44.3478 46.2482 46.3137

6 F 39.7727 41.7647 42.9762 42.1587

7 F 44.125 44.6667 43.5898 43.6742

8 F 41.1667 42.2917 41.5536 39.4447

9 F 41.619 45.1304 41.803 43.173

10 F 38.7083 37.2083 38.7615 39.4606

11 F 38.5833 37.5417 38.22 38.214

12 F 38.125 38.875 38.6709 39.4718

13 F 42.8333 43.0417 42.7684 42.6061

14 F 35.7917 38.3333 36.8816 37.8219

15 F 33.3158 34.3125 30.0319 29.4278

16 M 43.7826 43.7619 43.5041 43.6543

17 M 49.7727 54.0952 50.7373 55.4451

18 M 28.5556 31.1176 28.8856 26.8333

19 M 33.7059 34.1765 34.6903 31.7301

20 M 38.6667 39.0435 37.7833 38.4417

21 M 41.1364 40.2609 38.3768 40.0405

22 M 52.9545 54.3913 54.9234 53.7414

23 M 44.125 42.6364 43.0367 42.6009

24 M 44.125 42.6364 43.0367 42.6009

25 M 44.625 42.7727 44.5337 43.3814

26 M 39.8261 41.875 42.2875 42.6104

27 M 40.2174 41.125 42.7546 42.9607

28 M 30.1176 34.4118 33.6941 31.9481

29 M 43.25 42.625 44.6222 44.6203

30 M 47.9048 49.1739 49.8551 49.8009

31 M 39.1304 38.0833 39.9209 39.7252

32 M 42.5217 46.0833 42.6268 42.7801

Research Question

Do the effects of Prime Type factor depend on the levels of the Target Type factor?

The researcher is interested in the Prime Type x Target Type interaction. For example, can a person name an aggressive word more quickly if it is preceded by a weapon word than if it word is preceded by a neutral word?

The Null Hypothesis

There is no significant interaction effect.

The Alternative Hypothesis

There is a significant interaction effect.

We will conduct a 2 (prime type) X 2 (target type) within-subjects ANOVA to evaluate the interaction effect.
 

Obtain the Raw Data

Copy the Data Set

Click the Raw Data section (It is listed on the left side of the web page: Weapons and Aggression): http://www.ruf.rice.edu/~lane/case_studies/guns/DATA.TXT

Highlight the variable names and all the scores. Then right click on the highlighted area and select Copy from the pop-out menu. Now you may minimize or close the Weapons and Aggression window.
 

Start a Word Processing Program

Start Microsoft Word by choosing Start \ Programs \ Microsoft Word.

Paste Raw Data

Choose Edit \ Paste. The raw data set will appear.

Save the File

To save the file, choose File \ Save as.

Save in: Select a preferred drive.
Save as type: click the down arrow and select Text only (*.txt)
Click save. Click Yes.
Exit Microsoft Word.

Import the File to SPSS

Start the SPSS. Choose File \ Read Text Data. The Open File dialog will appear. Select the drive and the file. Click Open. The Text Import Wizard window will appear.

Step 1: Does your text file match a predefined format?

No. The first line in our text file is variable names. Click the Next button.

Step 2: How are your variables arranged?

Delimited. Spaces are used to separate variables in our text file.

Are variable names included at the top of your file?

 Click "Yes". Click the Next button.

Step 3: The default selections are correct.

Click the Next button. 

Step 4: Which delimiters appear between variables?

Space (SPSS detects the type of delimiter). Click the Next button.

Step 5: Specifications for variable(s) selected in the data preview.

Click the Next button.  

Step 6: Click the Finish button. The data set will appear in the SPSS Data Editor window.

Note that there are empty rows. Click the row number and right click on it. select clear from the pop out menu. 

Clear all the empty rows. There will be 32 rows. Note that the numbers are highlighted.

Descriptive Statistics

Screen Data

Choose Analyze \ Descriptive Statistics \ Explore. Move the four dependent measures to the Dependent list: aw, an, cxew, and cxen.

Next, click the Plots button. In the Boxplots area, select Dependents together. In the Descriptive area, select Histogram. Select Normality plots with tests as shown below.   

 

 

Click Continue and OK.

Results

Examine Descriptive Statistics.

Mean    

Notice that it took less time to name an aggressive target word when it was preceded by a weapon prime (MAW = 40.9184) than when it was preceded by a non-weapon prime (MAN = 41.6395). The presence of a weapon word (such as "dagger" or "bullet") increases the accessibility of an aggressive word (such as "destroy" or "wound").

 

Prime	Target	Reaction Times
1  Weapon	1. Aggressive	MAW = 40.9184
2 Nonweapon	1. Aggressive	MAN = 41.6395
	2

 

A comparison of the CXEW and CXEN conditions reveals no evidence of a weapon prime for the nonaggressive target words. There was no difference in the reaction time it took to name a nonaggressive word for two prime types of words. 

 

Prime	Target	Reaction Times
1 Weapon
	2. Nonaggressive	MCXEW = 41.4576
2 Nonweapon
	2. Nonaggressive	MCXEN = 41.3356

 

Standard Deviation

The variability for the CXEN condition (Nonweapon/Nonaggressive) was larger (6.089) than the other three conditions. 

Boxplots

Examine the length of the box. What do you observe?

Examine the outliers. Note that five outliers were detected in the Nonweapon/Nonaggressive condition.

Normal Probability Plot for the Dependent Measure in Each Conditions

AW:  the Weapon/Aggressive condition

AN: the Nonweapon/Aggressive condition 

 

CXEW: the Weapon/Nonaggressive condition

 

CXEN: the Nonweapon/Nonaggressive condition.

Note that the data do not fall exactly on this line. However, the deviations are not extreme.

 

Part Two     Inferential Statistics

Perform a 2 (prime type) X 2 (target type) within-subjects ANOVA, with aw, cxew, an, cxen referring to the cells of the following model.

Choose Analyze \ General Linear Model \ Repeated Measures. In the Within-Subject Factor Name textbox, type in "prime". Number of Levels: Type "2" as shown below.

Click the Add button.  In the Within-Subject Factor Name textbox, type in "target". Number of Levels: Type "2". Click the Add button.

Next, click the Define button as shown below.

Follow the order to enter the variables.

Select the variable aw and click the right arrow. 

Select the variable cxew and click the right arrow. 

Select the variable an and click the right arrow. 

Select the variable cxen and click the right arrow. 

To plot a line plot of interaction between Prime Type and Target Type, click the Plots button. Select the variable prime as Horizontal Axis. Select the variable target as Separate Lines. Click the Add button as shown below.

Click Continue. Click the Options button. In the Display area, click Descriptive statistics and estimates of effect size. Click continue and OK. 

Results

Descriptive Statistics 

Tests of Within-Subjects Effects

The interaction effect was significant, F(1,31) = 4.719, p = .038, partial .

Visualize the Interaction

Note that the lines plotted on the graph cross. It is a disordinal interaction (the lines cross). 

 1. It took less time to name an aggressive target word when it was preceded by a weapon prime than when it was preceded by a non-weapon prime. Notice that the slope of the line is steeper.

 2. There is no significant difference in the reaction time it took to name a non-aggressive word given two prime types of words.  Notice that the slope of the line is flat.

Simple Effects

A simple effects test is usually done after a statistically significant interaction test. The computation involves analyzing  the effect of one factor at each level of the other factor

1. Examine the simple effects of "prime type" on reaction time at the first level of the Target Type factor.

The slope of the line is steeper. The plot suggests that it took less time to name an aggressive target word when it was preceded by a weapon prime than when it was preceded by a non-weapon prime.

2. Examine the simple effects of "prime type" on reaction time at the second level of the Target Type factor.

The slope of the line is flatter. The plot suggests that there is no significant difference in the reaction time it took to name a non-aggressive word given two prime types of words. 

  Part Three    Q and A

Open the web page: Weapons and Aggression. Choose Descriptive Statistics, Inferential Statistics, and Interpretation from the list to the left and answer the associated questions. 

Web Resources
 

• SPSS Course Content by Lee A. Becker

Choose ANOVA Repeated Measures.

http://web.uccs.edu/lbecker/SPSS/content.htm