How many observations are needed

I think this will work okay if you have a collinearity problem and the confidence intervals on the parameters let you know whether the parameter value could be 0. Worry about model misspecification and always check the residuals. Frank Harrell is an active member of this site.

So i hope this question gets his attention and we can then hear directly from him. One scenario would be that all your parameters have about the same estimated magnitude of effect, but their uncertainties vary so that some are significant and others are not. You definitely don't want to conclude in this case that "variables A and B are important, variables C, D, and E are not". The CIs will give you this information. Show 2 more comments. Michael R. Chernick Michael R. Chernick I added my correlation matrix.

Do you think with this correlation matrix doing regression is reasonable? Just I want to find any possible relation between independent variables and dependent variable. The estimates will probably have large variance and so statitical significance should not be the focus.

Ypu could look at regression diagnostics for collinearity. That might help. But I would recommend looking at a variety of subset models to see how the fit changes and which combinations of variables seem to do well and do poorly. I really think bootstrapping the data will show you something about the stability of the choice of predictors. I think you just want to see if there is one or two variables that seem to stand head a shoulders above the rest.

But you may nit find anything. Since there is some correlation between these predictors, presumably their estimated coefficients are "worth" less than 1 degree of freedom. And what about, say, regression splines or other local regression: do we have to account for the fact that only a subset of observations is used in construction of the components?

And if we use a kernel to apply weights to predictors, does that affect the effective number of observations used? Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. Featured on Meta. Multiply the result with the value from Step 8. The Z value of 1. Square the desired accuracy level. For a desired accuracy level of 5 percent, this will be 0. Divide the answer from Step 9 with the value from Step 10 to get the minimum required number of observations for work sampling.

In this case, 0. Round up any fractional result to the next whole number. For the value of This means that the process must be observed at least times to record enough observations to have a 95 percent confidence level of any information recorded about the event that only occurs 10 percent of the time, plus or minus 5 percent. This calculation does assume that the events being observed are independent of each other.

If the events are dependent upon each other, such as one failure causing another failure right after it, the actual number of observations required to get enough data will be fewer than the value found by this equation.

My expertise includes product data management software. The teacher may need time to reflect on the new information, to plan new lessons in advance, and to practice new techniques before it would be possible to observe differences in the classroom. In our example, perhaps your first data collection period is in September, your PD is in October, and your second data collection is in January, looking for changes in behavior.

Of course, it can be helpful to use a combination of data collection to paint a fuller picture. Creating the most appropriate data collection plan for your school or district is an extremely important first step that should not be overlooked.

Hopefully, the guidelines discussed above will help you create a schedule that supports your goals. Please let us know what has worked well for you and share any feedback you have on our suggestions. His research interests include evaluation of educational technology, critical media literacy, student creation of multimedia texts, and the role of genre in student composition. Each month FCIT publishes a newsletter with short articles on teaching and learning with technology, using digital content in the classroom, and technology integration.

Subscribe today! The subscription form will open in a new window. When you have subscribed, you can close the new window to return to this page. Email: TIM fcit. How many observations do I need?