In this case, physician is apparently a factor with three levels, so summary.aov() gives you a sequential ANOVA, equivalent to what you'd get from anova(). There no simple relationship between the F-statistic for physician, which has 2 df in the numerator, and the two t's. (By the way, I doubt whether a sequential ANOVA is what's wanted here.)
Regards, John
At 09:17 AM 12/6/2003 -0800, Spencer Graves wrote:
The square of a Student's t with "df" degrees of freedom is an F distribution with 1 and "df" degrees of freedom.
hope this helps. spencer graves
Alexander Sirotkin [at Yahoo] wrote:
I have a simple linear model (fitted with lm()) with 2 independant variables : one categorical and one integer.
When I run summary.lm() on this model, I get a standard linear regression summary (in which one categorical variable has to be converted into many indicator variables) which looks like :
Estimate Std. Error t value Pr(>|t|) (Intercept) -3595.3 2767.1 -1.299 0.2005 physicianB 802.0 2289.5 0.350 0.7277 physicianC 4906.8 2419.8 2.028 0.0485 * severity 7554.4 906.3 8.336 1.12e-10 ***
and when I run summary.aov() I get similar ANOVA table : Df Sum Sq Mean Sq F value Pr(>F) physician 2 294559803 147279901 3.3557 0.04381 * severity 1 3049694210 3049694210 69.4864 1.124e-10 *** Residuals 45 1975007569 43889057
What is absolutely unclear to me is how F-value and Pr(>F) for the categorical "physician" variable of the summary.aov() is calculated from the t-value of the summary.lm() table.
I looked at the summary.aov() source code but still could not figure it.
Thanks a lot.
__________________________________
New Yahoo! Photos - easier uploading and sharing.
______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help
______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help
----------------------------------------------------- John Fox Department of Sociology McMaster University Hamilton, Ontario, Canada L8S 4M4 email: [EMAIL PROTECTED] phone: 905-525-9140x23604 web: www.socsci.mcmaster.ca/jfox
______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help
