Independent -means t-test:

used when there are two experimental conditions and different participants were assigned to each condition. also referred to as the independent-measures or independent-samples t-test

Dependent-means t-test:

used when there are two experimental conditions and the same participants took part in both conditions of the experiment. also referred to as the matched-pairs or paired-sample t-test.

calculating with standard error* : small standard error=most samples similar means

Assumptions of the t-test

  • The sampling distribution is normally distributed. In the dependent t-test this means that the sampling distribution of the differences between scores should b normal. not the scores themselves.
  • The independent t-test, because it is used to test different groups of people, also assumes: homogeneity of variance (variances in these populations are roughly equal), scores are independent (because they come from different people).

* Standard error: the standard deviation of sample means. It is a musure of how representative a sample is likely to be of the population.  As sample get large (greater than 30), the sampling distribution has a normal distribution with a mean equal to the population mean(=central limit theorem)