Relationship between Statistical Significance and Effect Size

Statistical significance and effect size are two important concepts in forensic psychology research. Statistical significance refers to the probability of obtaining a result as extreme or more extreme than the one observed, assuming the null hypothesis is true. Effect size refers to the magnitude of the difference between two groups or the strength of the relationship between two variables.

The relationship between statistical significance and effect size is complex and depends on a number of factors, such as the sample size, the power of the study, and the variability of the data. However, in general, statistical significance is more likely to be obtained when the effect size is large.

For example, consider two studies investigating the relationship between antisocial personality disorder (ASPD) and recidivism. The first study has a sample size of 100 participants, while the second study has a sample size of 1,000 participants. The first study finds a statistically significant relationship between ASPD and recidivism, while the second study does not. This is likely because the second study has more power, meaning that it is more likely to detect a statistically significant effect, even if the effect size is small.

Even though the first study found a statistically significant relationship between ASPD and recidivism, the effect size may be small. This means that the relationship between the two variables is weak. In contrast, the second study may have found a non-statistically significant relationship between ASPD and recidivism, but the effect size may be large. This means that the relationship between the two variables is strong.

Importance of Effect Size in Statistical Significance of Forensic Psychology Research

Effect size is important in forensic psychology research because it provides information about the magnitude and practical significance of the findings. Statistical significance only tells us whether the results are likely to have occurred by chance. It does not tell us how important or meaningful the results are.

Effect size can be used to determine whether a treatment or intervention is likely to be effective in real-world settings. For example, if a study finds that a new treatment for depression reduces depressive symptoms by 10% on average, this is likely to be a meaningful effect size. However, if a study finds that a new treatment for depression reduces depressive symptoms by 2% on average, this is likely to be a small and insignificant effect size.

Example Studies

Here are two examples of forensic psychology research articles where effect size was reported:

• Study 1:“The Relationship Between Antisocial Personality Disorder and Recidivism in a Prison Sample” (Edens, Kelley, Lilienfeld, Skeem, & Douglas, 2014)

This study investigated the relationship between antisocial personality disorder (ASPD) and recidivism in a sample of 300 male prisoners. The study found a statistically significant relationship between ASPD and recidivism, with an effect size of 0.35. This effect size is considered to be medium.

• Study 2:“The Effectiveness of Cognitive-Behavioral Therapy for Reducing Recidivism in Juvenile Offenders” (Gallagher et al., 2011)

This study investigated the effectiveness of cognitive-behavioral therapy (CBT) in reducing recidivism in a sample of 200 juvenile offenders. The study found that CBT was effective in reducing recidivism, with an effect size of 0.42. This effect size is considered to be large.

Conclusion

Effect size is an important concept in forensic psychology research. It provides information about the magnitude and practical significance of the findings. Even though a study may find a statistically significant relationship between two variables, the effect size may be small and insignificant. This means that the relationship between the two variables is weak and may not have any practical implications.