T-test report

t-test project: psy3020

Research Study Overview The goal of this research study is determine if CBT (cognitive behavior therapy) is effective in treating with people with

depression.

Purpose The purpose of this study is to show that 6 CBT treatments over a 12 week time period can reduce the symptoms of

depression in adults with physician diagnosed clinical depression.

For this study, researchers had a participant pool included 112 people who self-selected to be involved in a study for the

treatment of depression. No compensation was provided to participants. All measures and treatment were free to all

participants. To be considered for the study, participants must meet the inclusion criteria:

 Participants were suffering from physician diagnosed (e.g. DSM-IV, ICD-9) clinical depression.

 If participants were receiving pharmacological treatment for their depression, they had to be on

pharmacological treatment for at least 4 weeks prior to study.

 Participants had to have current episodes of depression lasting at least 6 months.

 Participants could not be currently involved in another psychological treatment.

A sample of 40 participants (22 females, and 18 males) was randomly selected from the pool for this study. The age of

the participants range from 22 – 39 years with an average of 30 years old. Participants reported current episodes of

depression lasting a mean of 17.47 months (SD ¼ 28:75).

One month prior to CBT treatment, each participant was given a measure of depression. One month after CBT

treatment, the depression measure was re-administered to all participants.

The depression measure is scaled from 1– 20 with higher scores indicating more depression. Scores from 1-7 are

considered low depression, scores from 8 – 14 are considered moderate depression, and scores 15 and above are

considered severe depression.

Descriptive Statistics

The Descriptives below give us an overview of the data. The Descriptive Statistics table displays the means, standard deviations, and other statistics of the depression ratings before the CBT treatment (Pre) began, and after treatment (Post). Use the descriptive statistics and the histograms to describe the pre and post results.

Descriptive Statistics

Pre Post

Valid 40 40

Mean 13.125 9.850

Median 12.500 10.000

Mode ᵃ 11.000 8.000

Std. Deviation 3.510 1.994

Minimum 8.000 6.000

Maximum 19.000 14.000

25th percentile 10.000 8.000

50th percentile 12.500 10.000

75th percentile 16.250 11.000

Descriptive Statistics

Pre Post

ᵃ More than one mode exists, only the first is reported

Distribution Plots

Pre – Depression scores prior to CBT treatment

Post – Depression scores after CBT treatment

Paired or dependent samples t-test

The table displays the results of the t-test. It contains the t -test results, the degrees of freedom, the p-value of the t- test, and the effect size Cohen’s d. The plot shows the differences in the mean between the two time periods. Use the results determine if the null hypothesis is true.

Paired Samples T-Test

Measure 1 Measure 2 t df p Cohen's d

Pre - Post 6.974 39 < .001 1.103

Note. Student's t-test.

Descriptives Plots

Pre - Post