This now becomes ANCOVA -short for analysis of covariance. We can do so by adding our pretest as a covariate to our ANOVA. We'd now like to examine the effect of medicine while controlling for pretreatment blood pressure. The relation between pretreatment and posttreatment blood pressure could be examined with simple linear regression because both variables are quantitative. This variable should therefore be taken into account as well. Now, posttreatment blood pressure is known to correlate strongly with pretreatment blood pressure. Our company wants to know if their medicine outperforms the other treatments: do these participants have lower blood pressures than the others after taking the new medicine? Since treatment is a nominal variable, this could be answered with a simple ANOVA. The data -partly shown below- are in blood-pressure.sav. They tested their medicine against an old medicine, a placebo and a control group.
SPSS ANCOVA Output - Between-Subjects EffectsĪ pharmaceutical company develops a new medicine against high blood pressure. There is a homework assignment to help you practice using one-way ANOVA on the Moodle site.SPSS ANCOVA – Beginners Tutorial By Ruben Geert van den Berg under ANOVA & Statistics A-Z Note that the Twenty Dollars condition will receive both an a and a b. Give an "a" subscript to all the groups listed under Subset 1 (Control and Twenty Dollars) andĪ "b" to all the groups listed under Subset 2 (Twenty Dollars and One Dollar). To use that information to make the subscripts: The homogeneous subsets output shows you groups of means that do not differ significantly from each other. Fortunately, some of the SPSS output can be of help here: In the table above, we show that the Control Condition is different from the One Dollar condition by giving them different subscripts, and we show that those two groups do not differ from the Twenty Dollar condition by giving the Twenty Dollar condition both subscripts. The subscripts presented next to the means can sometimes seem like a logic puzzle, so think through them carefully. The title of a table is presented below the word "Table", double-spaced, and is capitalized. A sample Google Doc with an APA-style table can be found here.Įvery table must be numbered, and must be referred to in the text (e.g., "As the means in Table 1 indicate."). 05 according to Tukey’s Honestly Significant Difference.Ī tutorial for how to make an APA-style table in MS Word is here. 
Means that do not share subscripts differ by p <.
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