Inferential Statistics

Statistical hypotheses

Using symbol for mean: μ

H₀: μ_L ò.= μ_R

H₁: μ_L > μ_R

_{L and R are the two conditions (specific example not general symbols): L = large writing (intervention), R = regular writing (control). It is expected that large font increases test scores}

_{Independent samples t test}

Compares the means of two independent groups in order to determine whether there is statistical evidence that the associated population means are significantly different

Confidence level = 1-significance level

• Zero in the confidence interval →→ do not reject the null hypothesis

• Zero not in the confidence interval →→ reject the null hypothesis

Assumptions of the t test

Sample is random

Dependent variable is of interval or ratio measurement level

Chi squared test of homogeneity → used when the DV is categorical and a t test cannot be used

• Null hypothesis: the distribution of answers in the control condition is equal to the distribution of answers in the treatment condition. ie, the treatment has no effect

• Measure of effect size: Cramer’s V. Values vary between 0 and 1, measures the strength of the relationship between the categorical variables

The two groups are independent

Scores in the groups are normally distributed

Scores in both groups have equal spread