Lecture 1: General Linear Model Flashcards
What are the assumptions of a t-test?
- continuous DV
- SE only valid if variance is not different between groups (homoscedasticity)
- subjects must be independent, otherwise SE formula not valid (cannot be tested, thinking exercise)
- look up t-statistic under $H_0$ but only if DV is normally distributed in both groups
Why is there a translational problem between basic and applied research?
- communication and shared language → communication issues between scientists in basic & applied
- replicability of findings → replication problems with many psychological findings - stability is crucial in the translational process
- establishing Causality → establishing causality is difficult since much of research is focusing on correlations
- unclear external validity → often mentioned that non-clinical samples is not beneficial
- fat-handedness problem → fat-handedness of psychological treatments - treatments often affect multiple processes, they do not operate in isolation
How does the t-distribution change shape based on the df values?
The more df the narrower it becomes, the less df the wider it becomes
What is b0?
The intercept and the expected/ average score on the DV when the IV is 0 o
Error
The difference between the observed and the expected score
What are the assumptions for the GLM?
- DV continuous
- variance of residuals equal at all levels of x (homoscedasticity)
- data is independent
- residuals normally distributed
What are the assumptions for the factorial ANOVA?
- DV continuous
- variances of DV equal in all groups
- data of all subjects is independent of each other
- DV is normally distributed in each group
What is b1?
The score on the dependent variable when the independent variable increases by 1 or the difference in averages of the different groups in the IV
How does the GLM work?
It creates a line that best fits with the observed data, results found to be the same as for the linear regression as the the t-test
What does the t-test test?
Whether the differences in averages across the groups is significant. Formula is= (y group 1- y group2)/ se
Standard error
√(sd²1/N1)+ (sd²2/N2)
What needs to be interpreted for a t-test?
- Look at the means to see the direction
- Check equal variances
- Look at the F values and p values to see significance
How would this be interpreted?
Self-esteem at posttest differed significantly between running and sitting
Self-esteem at posttest on average higher for running than for sitting
What is y(i)?
The observed score for the dependent variable
What needs to be interpreted for a linear regression?
The unstandardized b coefficients and the value and p value
How could we report regression analysis (does not need to be APA on the exam)?
- Intervention predicts self-esteem at posttest, F(1, 38) =
4.22, p = .047. - On average, self-esteem at posttest is higher for the running group than for the sitting group (b1), t(38) = 2.06, p =
.047.
What is the GLM with two independent variables?
y(i) = b0 + b1x(i) + b2z(i) + b3x(i)z(i) + error(i)
What is the interpretation of an interaction effect?
The effect of {intervention} differs between people across different groups
What needs to be interpreted for a factorial ANOVA?
Any significant main effects and the interaction effect
How can you interpret a plot for factorial ANOVA?
Average between groups= in difference between the mid point of the average lines
Interaction effect= the difference between the average lines at the starting point and end point
What is the sum of squares?
Deciphers how well the model fits the data, uses N-k-1
What is the total sum of squares?
The sum of squared differences between the observed and predicted values using the baseline model
What is the model sum of squares?
SST- SSR
What is R^2?
SSM/SST-> proportion of improvement with the predictive model compared to the baseline model
