Help Needed with HLM and Power

[MariaS]

I am an I/O Psych PhD student and have never had the opportunity to learn about HLM, but I am going to use it in my thesis.

I am looking for advice on how to conduct a power analysis to figure out how many participants I need.

A bit about the study:

It’s a policy-capturing study with 3 statements and 3 levels of each statement – resulting in a fully-crossed design of 27 scenarios. I’m going to repeat three, for a total of 30 policy capturing scenarios.

I’m looking both within people and between people, so I need enough participants that I can find those between groups effects.

Any advice would be greatly appreciated!

Maria S

[biggy128]

Maria,
Although I have not used this software in quite some time, you can download an application that does the power calculation at the following website:

http://sitemaker.umich.edu/group-bas...esign_software

As a general rule of thumb, minimal number of participants for an HLM design is 25 groups with 25 participants per group. A third level would obviously require a similar number of dimensions, meaning that your sample requirement will be very large.

Here are a few references to get you going:

Paterson, L, & Goldstein, H (1991). New statistical methods for analysing social structures: an introduction to multilevel models. British Educational Research Journal, 17, 387-393.

Snijders, T., & Bosker, R. (2000). Multilevel analysis. Thousand Oaks, CA: Sage Publications.

Cheers