Article 5.1

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Article 5.1

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5.1 t-Test for Independent Groups Communication in Relationships view STATISTICAL GUIDE To view The t-test is used to see if the difference between two means is romel statistically significant. There are multiple kinds of t-tests. In this curve, Dorthe exercise, we will focus on the t-test for independent groups. This To view t-test is used if the two means you are comparing are drawn from ronal and unrelated groups, e... groups formed by randomization of partici- pants. The dependent groups t-test, by contrast, compares means Berche 12 drawn from related groups, like having the same group take a test on two different occasions and comparing the mean score. The t-test for dependent groups is covered in Exercise 5.3. To use the t-test a number of assumptions need to be met. Two key assumptions are that (1) the data is normally distributed or nearly so. and (2) the data for the dependent variable is continuous, ie, on an interval or ratio scale. If these two assumptions (as well as others) are not met, then different statistical tests should be used to compare the two group means (e.g. see Unit VI). The t-test yields a p-value, which indicates the probability that chance or random sampling errors created the difference between the means As with many statistical tests, most researchers consider a difference to be statistically significant when p<.05. When it does, the null hypothesis (that the group means are the equal) is rejected. As with correlation, when researchers present t-test results in a table (like Table 1 below), they often note statistically significant results with an asterisk or some kind of superscript. It is generally safe to assume that if a result has no superscript then the result is non-significant. Still, reading table notes is necessary, so you can make sure you know what certain symbols in the table mean. Like many things in statistics, the t-test for independent groups goes by multiple names. This can be confusing. The t-test for independent groups is also called: independent t-test for two samples, independent- samples t-test, and Student's t-test. 119

INTERPRETING BASIC STATISTICS EXCERPT FROM THE RESEARCH ARTICLE The married sample comprised members of 100 heterosexual couples (54% were women and 46% were men) from a Midwestern university. The dating sample also consisted of members of 100 heterosexual couples (59% were women and 41% were men) from the same Midwestern university. All the married and dating couples were Euro-American. A researcher selected subjects in a haphazard fashion and asked them to complete a short survey. ... The mean age of the sample was 26.7 years (SD-2.6). The Affectionate Communication Index is a 19-item index that... assesses the amount of verbal and nonverbal affectionate communication and support on a 7-point.. scale, with anchors of 1 =partners always engage in this type of affectionate activity to 7=partners never engage in this type of activity. [Thus, lower scores indicate more affectionate communication Table 1 shows the results for the nonverbal activities.] Table 1 Dating and Married Individuals' Reports of Nonverbal Affectionate Communication Item MSD Hold hands Dating 100 3.7 1.9 3.3 Married 100 2.9 1.7 Kiss on the lips Dating 100 2.9 4.9 Married 100 2.0 1.1 Kiss on the cheeks 100 3.6 1.6 4.5 Married 100 2.7 1.3 Give massages to each other Dating 100 42 1.8 5.00 Married 99 2.5 1.8 Put arm around shoulder Dating 100 3.6 4.60 Married 92 2.5 1.5 Hug each other Dating 100 2.5 1.6 2.0" Married 100 2.1 1.2 Sit close to each other Dating 96 2.9 1.6 3.99 Married 100 2.0 1.6 Look into each other's eyes Dating 100 3.3 1.6 1.0 Married 100 3.0 1.8 Wink at each other Dating 100 4.7 23 1.7 Married 96 4.2 1.9 *p<.5. 'p<.001 t ino 1.5 Dating wa 00 1.8 MNNNN Noomo ο αν η Οι Ν ι :

GROUP DIFFERENCES STUDY QUESTIONS Factual Questions 1. If you visually inspect Table 7. Should the null hypothesis be 1, which group had a higher rejected for winking at each mean score for kissing on the other? lips (i.e., on average, which 8. How many of the differences group reported less kissing on in Table 1 are statistically sig. the lips)? nificant at the .05 level but not 2. Is the difference between the significant at the .001 level? two means for kissing on the 9. The differences between the lips statistically significant? If means for the item in A and B. yes, at what probability level? are statistically significant. For 3. Should the null hypothesis which one is the significance be rejected for kissing on the at a higher level? Explain your lips? If yes, at what probability answer. level? A. The difference for hug. 4. Is the difference between the two means for hugging each ging each other. B. The difference for sitting other statistically significant? If close to each other yes, at what probability level? 5. Should the null hypothesis 10. For which of the following can be rejected for hugging each we reject the null hypothesis other? If yes, at what prob- with greater confidence? ability level? A. The difference for hugging 6. The differences are not sta- each other. tistically significant for which B. The difference for holding items? hands. Questions for Discussion 11. The group difference for Which three are descriptive kissing on the cheeks is sta- statistics? (Note: If you have tistically significant at the a statistics textbook, you may .001 level . Logically, is it also want to consult it.) significant at the .05 level? 13. The table contains five types (Note: If you have a statistics of statistics (n, M, SD, t, and textbook, examine the table p). Which two are inferential of critical values of t to help statistics? (Note: If you have you determine the answer to a statistics textbook, you may this question.) want to consult it.) 12. The table contains five types of 14. The researcher states that she statistics (n. M, SD, t, and p). selected the individuals for

INTERPRETING BASIC STATISTICS this study "in a haphazard fashion." What is your under- standing of this term? 15. For all items for which there are statistically significant dif- ferences, the means for dating couples are higher than the means for married couples. If you had planned this study, would you have hypothesized this result? (Recall that higher scores mean lower frequen- cies of behavior.) Explain. NOTE 1 Punyanunt-Carter, N. M. (2004). Reported affectionate communication and satisfaction in marital and dating relationships. Psychological Reports, 95, 1154-1160. Reprinted by Permission of SAGE Publications, Inc.