Psychology week 7 assignment

1

Psychology week 6 assignment 2

Barbara Maclure

Dr, Kelly

12/07/2025

Methods: Data analysis

The question of interest in this project was the following:

Does the intervention in the program decrease the symptoms of youth anxiety between intake and discharge based on the Generalized Anxiety Disorder-7 (GAD-7) scale? Comment by Kelly Schmitt: Don’t have text in bold other than headings or sub-headings per APA guidelines

The GAD-7 is a total anxiety score, according to the program evaluation codebook, the range of the score is 0-21, with higher scores representing more severe symptoms of anxiety. The dataset variables of interest were pre- and post-GAD-7, namely, GAD7pre and GAD7post.

Each participant was given a difference score (GAD7_diff = GAD7_pre - GAD7_post) in such a way that a positive value was used to demonstrate the decrease in the number of anxiety symptoms throughout the program.

Before hypothesis testing, several data cleaning and screening processes were done. To start with, there were trends of missing data to be analyzed with GAD7 pre and GAD7 post. Out of the 100 participants in the dataset, 97 participants had both pre and post-test GAD-7 scores, and 3 participants did not have any post-test data. Complete cases were thus considered in the analyses and those records where either of the pre- and post-test had a missing value were deleted with the listwise deletion (Xu et al., 2015).

Second, the difference scores were examined on whether they have outliers. A z-score was derived on GAD7_diff in each participant, and a score where |z| > 3 was considered as a potential outlier. Two subjects were considered as possible outliers, but they were retained since they were realistic variation of treatment response as opposed to apparent data entry mistakes. Comment by Kelly Schmitt: This is ok but the process discussed to use for assignment purposes is box plots

Third, the difference scores were tested on whether they were normally distributed to know the inferential test to use. Skewness, kurtosis, and visual examination of a histogram of GAD7_diff were used to check normality. The difference scores were highly skewed positively (skewness = 2.37) and displayed significant leptokurtosis (kurtosis = 12.25) meaning that there were quite a few values concentrated at the lower part having a long right tail. The histogram (see Figure 1) proved the fact that the distribution was significantly not normal. Since the normality assumption was evidently broken, a parametric paired-samples t-test was inappropriate. Comment by Kelly Schmitt: Use shapiro-wilk on differnce scores and Q-Q plot to assess normality

Since the difference scores were not normally distributed, the Wilcoxon Signed-Rank test was chosen as the primary statistical test to compare the pre- and post-intervention GAD-7 scores. The analysis of the test was performed on the participants who had non-zero difference scores (n = 93) at a two-tailed alpha =.05. The sum of the positive and negative signed ranks gave the Wilcoxon test statistic (W), and a standardized z value was calculated by using the large-sample approximation. To measure the magnitude of change, the effect size was calculated as . Since it was not a normal distribution, the descriptive statistics are provided as medians and interquartile ranges (IQRs) of GAD7_pre and GAD7_post.

Figure 1. Distribution of GAD-7 difference scores (pre minus post).

Results

Descriptive statistics revealed that the youth had reported relatively elevated levels of anxiety symptoms at the intake and slightly reduced symptoms at discharge.

Figure 2 represents the simple summary graph of pre- and post-test GAD-7 median scores, which visually indicates that there is a slight downward change in anxiety symptoms across time.

Wilcoxon Signed-Rank test, to determine whether the change was statistically significant. The test obtained a Wilcoxon value of W =37 based on the 93 non-zero difference scores. The standardized test statistic is z = -8.23, which has a p < .001 (two-tailed) using the large-sample approximation. The effect size associated with it was r = -.85, which implies an exceedingly substantial magnitude of change; negative sign depicts that post-test scores were less than pre-test scores (Durango & Refugio, 2018). Collectively, these findings demonstrate statistically significant and practically significant decrease in GAD-7 anxiety symptoms between intake and discharge, indicating that the program was effective in enhancing the youth anxiety outcomes. Figure 2. Median GAD-7 anxiety scores at pre- and post-intervention. Comment by Kelly Schmitt: This value is different than what I compute. Make sure to double check for week 7 Comment by Kelly Schmitt: You say negative r indicates post < pre, but your diff was defined as pre–post (positive indicates improvement). Be sure to clarify.

Comment by Kelly Schmitt: Good start. Also include histograms, Q-Q plot, and box plots

References

Durango, A., & Refugio, C. (2018). An empirical study on Wilcoxon signed rank test.  J. Negros Orient. State Univ., (December).

Xu, S., Lu, B., Baldea, M., Edgar, T. F., Wojsznis, W., Blevins, T., & Nixon, M. (2015). Data cleaning in the processing industries.  Reviews in Chemical Engineering,  31(5), 453-490.

Median GAD-7 Anxiety Scores Pre- and Post-Program

Median_GAD7

Pre Post 10 9

Time

GAD-7 Score