PS211 - Exam 2 - Independent Samples Design

two-sample experiment

• compare two independent samples

• both sample means and SD known

one-sample experiment

• compare pop to sample

• sample mean, sample SD, pop mean known

between-subjects + which t-test

• independent samples

• diff individuals/not related

within-subjects + which t-test

• dependent samples

• groups related?DV more than once

assumptions of independent sample t-test

• DV measures interval/ratio

• population of raw scores form normal distribution

• populations have homogeneous variance

homogeneity of variance

statistical assumption that different samples have equal pop. variances

what does independent samples t-test determine about difference between means that we’ve obtained

if observed difference between two means is statistically significant

sampling distribution of differences between means

• null = mean of the sampling distribution = the difference between the two population means

difference between N and n

• N = population size

• n = sample size

pooled variance

• mean and estimated population variance for each condition

• weighted average

two ways to measure effect size

• cohen’s d

• proportion of variance accounted for

proportion of variance accounted for

percentage of total variance in the DV that is explained by IV

what does a t-test do

• test the difference between two independent group sin an experiment on a single DV measure

  • determine IV has systematic effect on DV

comparing groups

variability between groups/variability within groups

variability between groups

due to manipulation

variability within groups

due to random error