This example, taken from huntsberger and billingsley1989, p. Pdf the differences and similarities between twosample ttest. Paired samples t the basics similar to single sample t or zscore to compare sample to population based on difference scores instead of raw scores o matched pairs individuals from different groups matched by key characteristics o prepost designs goal. For a matchedpairs or casecontrol study, the response for each test subject and its matched control subject must be in the same case in the data file. In this example we present the steps for using onesample t test. Let us consider a simple example of what is often termed prepost data or pretest posttest data. Suppose you wish to test the effect of prozac on the wellbeing of depressed individuals, using a standardised wellbeing scale that sums likerttype items to obtain a score that could range from 0 to 20. For each paired test, specify two quantitative variables interval level of measurement or ratio level of measurement. One sample t test a one sample t test can be used to compare a sample mean to a given value. Comparison of independentsamples t test and pairedsamples t test using spss. A paired ttest is used to compare two population means where you have two samples in which observations in one sample can be paired with observations in the other sample. A researcher is interested in the effectives of a new drug to reduce ldl levels in men with high. The twosample ttest also called independent samples ttest and the paired ttest are.
A beverage company is interested in knowing the performance of a discount program on. The sample size is at l east 30 the effect size the mean of the di fference divided by. Chumney with a brief overview of the paired samples t. The paired t test, or dependant sample t test, is used when the mean of the treated group is computed twice. Remarks are presented under the following headings. The pairedsamples t test in spss statistics determines whether means differ from each other under two conditions. Onesample and pairedsample ttest matlab ttest mathworks. The salary of 6 employees in the 25th percentile in the two cities is given. Paired samples t and wilcoxon tests are analytic methods that are appropriate for within subjects research designs, so lets start with a quick. Given that the assumptions of independent samples and normality are valid, this. The paired samples t test compares two means that are from the same individual, object, or related units. The correct bibliographic citation for the complete manual is as follows. Although this fact is well documented in statistical.