Lecture 4 - Longitudinal assessment

Question 1

What is the equation for the standard error of prediction (SEp)

Answer 1

SEp = sigma * SQRT(1-(Rxx * Rxx))

Where sigma is the SD of the test and Rxx is the reliability coefficient

Question 2

What FOUR pieces of INFORMATION do we need to determine whether a change in scores over time represents clinically meaningful change?

Answer 2

We need

1. the PTS at time 1
2. the PTS at time 2
3. the population standard deviation
4. a reliability coefficient for the test

(We use items 3 and 4 to determine the standard error of prediction)

Question 3

What FOUR STEPS are required to determine whether a change in scores represents clinically significant change?

Answer 3

1. Determine the PTS at both time points
2. Calculate the Standard error of prediction (SEp) that applies to the PTS at time point one
3. Use the SEp to calculate confidence intervals to PTS at time point one
4. Check whether the PTS at time point two falls within the confidence intervals you calculated at step three

Question 4

Describe how reliable changes indices work

Answer 4

RCIs take the difference between two scores and converts it to an index that takes into account measurement error.

If RCI exceed certain thresholds, the evidence of change is assumed

Question 5

What RCI threshold is used to signify change at 90% confidence?

Answer 5

RCI +/- 1.645