Inferential Statistics

Overview

T-testSPSS Steps

• Open SPSS data file• Click on ANALYZE• Click on COMPARE MEANS• Click on INDEPENDENT

SAMPLES T TEST• Select continuous dependent

variable• Select nominal grouping

variable • Define groups (1 and 2)• Click OK

Interpreting Output

• Check means and group sizes• Look EQUAL VARIANCES

ASSUMED • Note t value, df, and

significance (two tailed)

If significance ≤ .05, report t = value, df = value, p = significance

Differences StudyWhat accounts for different oral proficiency

ratings?• ratings on informational interview are dependent

variable• student characteristics possible independent

variablesTheory--applied learning experiences enhance

student performance in the classroomHypothesis—completing an internship will increase

ratings on the informational interview

T-test Output

T-test Narrative

Hypothesis—Completing an internship will increase oral and written competency ratings.

Result—Completing an internship had no effect on one dimension (invention) of oral competency ratings (t = -.028, df = 56, p = .98).

Found no support for hypothesis.

ANOVASPSS Steps

• Open SPSS data file• Click on ANALYZE• Click on COMPARE MEANS• Click on ONE WAY ANOVA• Select continuous dependent

variable• Select nominal/ordinal factors• Click POST HOC TESTS• Select TUKEY and

significance level• Click CONTINUE• Click OK

Interpreting Output

• Note F ratio, df (between and within), and significance

If significance ≤ .05, report F(dfbetween,dfwithin) = value, p = significance

Tukey output indicates which groups are different from each other

Differences StudyWhat accounts for different written proficiency

ratings?• ratings on portfolio are dependent variable• different instructor possible independent

variablesTheory--instructor ratings should be uniform.Question—Will identity of instructor influence

ratings on the portfolio?

ANOVA Output

Tukey Output

ANOVA NarrativeHypothesis—Instructor teaching COM400 will not influence

oral and written competency ratings.

Result—Instructor teaching COM400 had an effect on one dimension (invention) of written competency ratings (F (4,100) = 11.98, p = .0001).

1 differed from 3 and 5; 2 differed from 3 and 5; and 3 differed from 4

Found no support for hypothesis.

CorrelationsSPSS Steps

• Open SPSS data file• Click on ANALYZE• Click on CORRELATIONS• Click on BIVARIATE• Select continuous dependent

variable• Select continuous independent

variable• Select PEARSON corr coeff,

two tailed test and flag significance correlations

• Click OK

Interpreting Output

• Look above or below the diagonal

• Note correlation coefficient and significance (two tailed test)

If significance ≤ .05, report r = value, p = significance and

strength of relationship

r = ≤ .39, weak relationshipr = .40-.69, moderate relationshipr = .70-.99, strong relationship

Relationship StudyWhat are you willing to do for a friend?• willingness to offer emotional support to a CSF

is the independent variable• willingness to offer instrumental support to a

CSF is a dependent variable THEORY—Social exchange theoryHypothesis—A relationship exists between

emotional support offered a CSF and instrumental support offered a CSF.

Correlation Output

Correlation NarrativeHypothesis—A relationship exists between emotional

support offered a CSF and instrumental support offered a CSF.

Result—A relationship exists between emotional support offered a CSF and instrumental support offered a CSF

• platonic friend (r = .65, p = .005) moderate• friends with benefits (r = .66, p = .004) moderate

Support was found for hypothesis.