In: Statistics and Probability
Describe the assumptions that should be met when deciding to use the t-test (i.e., scale of measurement; assumptions about variances of groups being compared; assumptions about group sizes; shapes of distributions.)
--- The assumption made regarding t-tests concerns the scale of measurement. The assumption for a t-test is that the scale of measurement applied to the data collected follows a continuous or ordinal scale, such as the scores for an IQ test.
--- The variances of the two populations should be equal
--- The two samples are independent. There is no relationship between the individuals in one sample as compared to the other
--- Both samples are simple random samples from their respective populations. Each individual in the population has an equal probability of being selected in the sample.
--- The data when plotted, results in a normal distribution, bell-shaped distribution curve. When a normal distribution is assumed, one can specify a level of probability (alpha level, level of significance, p) as a criterion for acceptance. In most cases, a 5% value can be assumed.
--- A reasonably large sample size is used. A larger sample size means the distribution of results should approach a normal bell-shaped curve.