Skip to main content

Independent Samples t-test

Independent Samples t-test

Researchers use the independent samples t-test to find out if there is a significant difference between two sets of data. In the behavioral sciences, the data are often two sets of scores on tests or survey items.

Significance can mean a lot of different things. In behavioral science, it is common to think of significance as a frequently occurring, and thus reliable, difference. Sometimes the language of statistics can be confusing. The independent sample t-test evaluates the differences between the arithmetic means of the two groups of scores, and assumes the scores are normally distributed.

Usually, a difference needs to be at least large enough that a score difference as large, or larger than the one obtained, occurs only 5% of the time by chance.

The calculations are usually done in spreadsheets like Excel or Google Sheets or in a program like SPSS. See the link below for a download about how to calculate a t-test.

You will find the following text in Chapter 16 of Creating Surveys. I also cover t-tests in Statistics for Counselors.

Creating Surveys

Create better surveys for work and school

BUY today   AMAZON

The statistical procedure results in a t-value and a p value. The larger the t-value, the more likely it is that the difference between the group means is significant. The p-value represents the probability that the t-value of the size obtained did not occur by chance. As in many cases, the p-value is reported based on a 95% probability that the t-value did not occur by chance. The p-value is usually reported by considering the likelihood that it occurs by chance greater or less than 5% of the time where 5% is written as .05. If the probability is less than .05 that a t-value as large or larger than the one obtained did not occur by chance, the researcher would report the results as p < .05. If the t-value was too small to meet the level needed for significance, the researcher would just report the finding as not significant (p > .05).

I and my colleagues have studied forgiveness. Suppose we found that people who attended a forgiveness seminar obtained higher forgiveness scores compared to those who did not attend.
Here’s how we might write the results (Chapter 16, Creating Surveys).

We found that people who did attended the forgiveness seminar were significantly more forgiving (M = 39, SD = 5) than were people who did not attend the seminar (M = 30, SD = 5), t (98) = 6.75, p < .05.

Applied Statistics: Concepts for Counselors


You can calculate the independent samples t-test by hand. If you are interested, click the download link for a pdf file.  t-test DOWNLOAD HERE

Also, here is an online calculator where you can enter two sets of values and obtain a t-test result.

Connections and Links to Resources

My Page

My Books   AMAZON

FACEBOOK   Geoff W. Sutton

TWITTER  @Geoff.W.Sutton

LinkedIN Geoffrey Sutton  PhD

Publications (many free downloads)
  Academia   Geoff W Sutton   (PhD)
  ResearchGate   Geoffrey W Sutton   (PhD)


Popular posts from this blog

Personal Self-Concept Questionnaire (PSQ)

  The Personal Self-Concept Questionnaire  ( PSQ )   Overview The Personal Self-Concept Questionnaire (PSQ) measures self-concept based on ratings of 18 items, which are grouped into four categories: Self-fulfilment, autonomy, honesty, and emotional self-concept. Subscales : The PSQ has four subscales 1. Self-fulfilment (6 items) 2. Autonomy (4 items) 3. Honesty (3 items) 4. Emotional self-concept (5 items)  👉 [ Read more about Self-Concept and Self-Identity] The PSQ is a Likert-type scale with five response options ranging from totally disagree to totally agree. Reliability and Validity In the first study, coefficient alpha = .85 and in study two, alpha = .83. Data analysis supported a four-dimensional model (see the four categories above). Positive correlations with other self-concept measures were statistically significant. Other notes The authors estimated it took about 10 minutes to complete the PSQ. Their first study included people ages 12 to 36 ( n = 506). In the second s

Student Self-Efficacy

  Assessment name:  STUDENT SELF-EFFICACY SCALE * Note. This post has been updated to provide an available measure of student self-efficacy. ———- Scale overview:  The  student self-efficacy scale i s a 10-item measure of self-efficacy. It was developed using data from university nursing students in the United States. Authors: Melodie Rowbotham and Gerdamarie Schmitz Response Type:  A four-choice rating scale as follows: 1 = not at all true 2 = hardly true 3 = moderately true 4 = exactly true   Self-efficacy is the perception that a person can act in a way to achieve a desired goal.  Scale items There are 10 items. Examples: I am confident in my ability to learn, even if I am having a bad day. If I try hard enough, I can obtain the academic goals I desire.   Psychometric properties The authors reported that their sample scores ranged from 25 to 40 with a scale mean of 34.23 ( SD  = 3.80. Internal consistency was high at alpha = .84. The authors reported the results of a principal compon

Mathematics Self-Efficacy and Anxiety Questionnaire (MSEAQ)

  Scale name: Mathematics Self-Efficacy and Anxiety Questionnaire (MSEAQ) Scale overview: The Mathematics Self-Efficacy and Anxiety Questionnaire (MSEAQ) is a 29-item self-report measure of both mathematics self-efficacy and mathematics anxiety. Author: Diana Kathleen May Response Type: Items are rated on a 5-point Likert-type scale following a “no response” option: 1 = Never 2 = Seldom 3 = Sometimes 4 = Often 5 = usually Sample items 1. I feel confident enough to ask questions  in my mathematics class. 6. I worry that I will not be able to get a  good grade in my mathematics course.   Subscales and basic statistics for the MSEAQ       Self-Efficacy M = 44.11, SD = 10.78, alpha = .93       Anxiety M = 46.47, SD = 12.61, alpha = .93       Total Scale M = 90.58, SD = 22.78, alpha = .96 Reliability: See the Cronbach’s alpha levels reported above. Validity: There were significant positive correlations with similar measures. The results of a Fa