Turn on suggestions

Auto-suggest helps you quickly narrow down your search results by suggesting possible matches as you type.

Showing results for

- Home
- /
- Analytics
- /
- Stat Procs
- /
- Power calculation in cohort study

Options

- RSS Feed
- Mark Topic as New
- Mark Topic as Read
- Float this Topic for Current User
- Bookmark
- Subscribe
- Mute
- Printer Friendly Page

🔒 This topic is **solved** and **locked**.
Need further help from the community? Please
sign in and ask a **new** question.

- Mark as New
- Bookmark
- Subscribe
- Mute
- RSS Feed
- Permalink
- Report Inappropriate Content

Posted 01-02-2018 07:34 AM
(3071 views)

Hi! I am performing a prospective cohort study in an existing cohort study. The sample of participants I can use from this existing cohort is 190. I am using a Cox model to analyze the data and to get a Hazard ratio. But now I want to know what the power of the study is. How can I calculate it? I can't find it on the internet...

So I am doing a prospective survival analysis (in an existing cohort) of 190 participants, the exposure is divided either into three categories and continuous and the outcome is yes/no.

After that, I also want to calculate the power of the study when it is stratified for some covariates.

I am using SAS, so maybe there is an option in SAS for this?

I hope some of you can help me. Thanks in advance!

1 ACCEPTED SOLUTION

Accepted Solutions

- Mark as New
- Bookmark
- Subscribe
- Mute
- RSS Feed
- Permalink
- Report Inappropriate Content

I would probably simulate it then.

You would run a whole bunch of simulations and determine the cutoff points. I actually coded this about 5 years ago for a clinical trial protocol and to determine the number of obs and when we could terminate early 🙂

I recall using a text book, I'll dig up the name and reference tonight, if someone else hasn't already answered this.

You can also look up Rick Wicklin's book on simulating data with SAS.

5 REPLIES 5

- Mark as New
- Bookmark
- Subscribe
- Mute
- RSS Feed
- Permalink
- Report Inappropriate Content

PROC POWER.

It looks like survival analysis.

Here's an example to get you started.

@hovliza wrote:

Hi! I am performing a prospective cohort study in an existing cohort study. The sample of participants I can use from this existing cohort is 190. I am using a Cox model to analyze the data and to get a Hazard ratio. But now I want to know what the power of the study is. How can I calculate it? I can't find it on the internet...

So I am doing a prospective survival analysis (in an existing cohort) of 190 participants, the exposure is divided either into three categories and continuous and the outcome is yes/no.

After that, I also want to calculate the power of the study when it is stratified for some covariates.

I am using SAS, so maybe there is an option in SAS for this?

I hope some of you can help me. Thanks in advance!

- Mark as New
- Bookmark
- Subscribe
- Mute
- RSS Feed
- Permalink
- Report Inappropriate Content

Thanks for answering. When I do this:

```
PROC POWER;
coxreg
hazardratio = 1.4
stddev = 1.2
ntotal = 190
eventprob = 0.25
power = .
;
run;
```

SAS says about the 'coxreg'; 180-322: Statement is not valid or it is used out of proper order. This nearly the same as in the example, what can I do? I am using SAS 9.4.. I think that is the problem? What else can I do?

- Mark as New
- Bookmark
- Subscribe
- Mute
- RSS Feed
- Permalink
- Report Inappropriate Content

What version of SAS/STAT do you have? If you're not sure, you can use the following code to check.

It's possible that it's an earlier version and you don't have this feature yet 😞

`proc product_status;run;`

- Mark as New
- Bookmark
- Subscribe
- Mute
- RSS Feed
- Permalink
- Report Inappropriate Content

I am using SAS 9.4 so I think it is not possible? What could I do to calculate the power of my survival analysis? Because Ive three groups and in PROC POWER; twosamplesurvival you only have two groups right?

- Mark as New
- Bookmark
- Subscribe
- Mute
- RSS Feed
- Permalink
- Report Inappropriate Content

I would probably simulate it then.

You would run a whole bunch of simulations and determine the cutoff points. I actually coded this about 5 years ago for a clinical trial protocol and to determine the number of obs and when we could terminate early 🙂

I recall using a text book, I'll dig up the name and reference tonight, if someone else hasn't already answered this.

You can also look up Rick Wicklin's book on simulating data with SAS.

Build your skills. Make connections. Enjoy creative freedom. Maybe change the world. **Registration is now open through August 30th**. Visit the SAS Hackathon homepage.

What is ANOVA?

ANOVA, or Analysis Of Variance, is used to compare the averages or means of two or more populations to better understand how they differ. Watch this tutorial for more.

Find more tutorials on the SAS Users YouTube channel.