Everyday Research Methods

The language of a liar

Many of us are somewhat familiar with the physiological lie detector--a machine that records physical signs of anxiety (such as sweating or blood pressure) while people answer questions.  More recently, research from psychologist Dr. James Pennebaker has demonstrated that psychologists can use natural language to distinguish liars from truth-tellers.

The research is discussed in this Huffington Post article.   The article explains that the researchers analyzed a set of stories (from court transcripts or journalism) that were known to be either  truthful or false.  They submitted the text of the stories to a computerized system known as LIWC (Linguistic Inquiry and Word Count).  The program can tally different types of speech (such as pronouns, verbs, positive or negative emotion words) in any type of text.  There were four differences between the language used in true and false stories: 

An analysis of the words used in these stories revealed a few reliable differences. Stories that were true had more words in them and more details than those that were fake.

The true stories had fewer emotion terms in them than the fakes.

The true stories had fewer verbs than the fakes.

Finally, the true stories had more first-person pronouns in them than the fakes.

For example, this last example was  supported by court transcripts, where they found:

defendants who were found guilty at trial but were later exonerated based on DNA evidence often used first-person pronouns. The expressed their innocence by talking about themselves. Defendants who were guilty of perjury used third-person pronouns (like he and she) as they tried to shift blame to other people.

a) What are the variables in this pattern of results?  What kind of study is this--correlational or experimental?

b) This study can be seen as an illustration of a "known groups" predictive validity study.  Can you explain how? What is being measured here, and how is the measure being validated?

 

Suggested answers:

a) The variables here are the different qualities of speech (such as number of words, number of verbs, or number of first-person pronouns), and the known truthfulness of the text. Both of these variables are measured--they occurred more or less naturally.  Therefore, this is a correlational study.

b) You could view qualities of speech (for example, the number of first-person pronouns) as an operational definition of "lying."  That is, the LIWC system can be seen as a lie detector.  To decide if this measure of lie detection is a valid one, the researchers used the known groups paradigm of recruiting examples of known liars and known truthtellers.  The fact that the liars and truthtellers showed the predicted differences in language use provides evidence supporting that the language use measure may be a valid measure of lying.  In this sense it is similar to the strategy that Beck and colleagues used when they confirmed that scores on the Beck Depression Inventory were higher for known groups of depressed people than for non-depressed people (as described in Chapter 5).    

Is tanning addictive?

A New York Times article discussed research from the journal Addiction Biology. It tests a theory claiming that tanning is addictive. The sample they used was

...a small group of people from tanning salons who said that they liked to tan at least three times a week and that maintaining a tan was important to them.

The researchers manipulated the type of tanning session that the participants would experience. In one session, the tanners experienced a “normal tanning session” and then answered several questions. Then on another occasion, the participants tanned but the researchers “blocked only the UV light” without telling the tanners of the manipulation.

The results of the study showed that:

The tanners ... expressed less desire to tan after the real sessions, indicating they had gotten their fill. But on days when the tanners were unknowingly deprived of the UV rays, their desire to tan after the session remained as high as ... before the session began.

In addition, the study found that tanner’s brain activity during the UV session (but not during the sham session) was consistent with areas of the brain that are related to addictions.

a.) What are the independent and dependent variables in this study? 

b.) Is this a within groups or independent groups design? 

c.) The study used only heavy tanners. What population does this sample represent? Why might the researchers have limited their sample to this group? What validity does this question address?

d.) What causal claim could the researchers be able to make? Does this hold up to the three causal rules?

Suggested answers:

a.)  The independent variable was UV exposure, which included two levels, exposure or no exposure to UV rays during the tanning session. One dependent variable was the participant’s desire to tan after the session. Another dependent variable was the participants’ brain activity .  

b.)  Within groups, repeated measures. We know this was repeated measures because the participants are exposed to each level of the variable. They tan with UV rays and then later tan without UV rays. One thing we don’t know is whether they counterbalanced or accounted for order effects.  

c.)  Heavy tanners were the experimenter’s “population of interest”, so it makes sense to limit the sample to only heavy tanners. This is an external validity concern. 

d.) According to the original NYTimes article, the researchers are testing the idea that there is something addictive about the UV rays that people receive during tanning. Specifically, this study seems to suggest that exposure to UV rays (versus the same tanning experience minus these rays) causes people to feel a reduced need to tan. Does the study have covariance? Yes, they found that a lack of UV ray exposure was associated with a desire to tan; Temporal precedence? Yes. The manipulation comes first and the desire to tan is measured immediately afterwards; Internal Validity? Yes. The article doesn’t address any confounds that they possibly eliminated. Order effects could have an effect on internal validity if all tanners were exposed first to UV rays in one session and not in the next session. Counterbalancing would control for these possible order effects.

(Guest Post by Kate Banford, University of Delaware)