Dear community, Apologies for my questions, I´m pretty newbie.
The thing is, I was trying this lm: mod.lm <- lm(df$res ~ df$var1+ df$var2 + df$var3 +fact1:fact2) And factors are like this: > table(fact1) a b c 3 90 83 > table(fact2) a b c 4 87 85 Because of the interaction, i obtain the following error, (I guess...): > summary(mod.lm) Residuals: Min 1Q Median 3Q Max -3.0163 -1.1604 -0.1741 0.9281 3.8957 Coefficients: (3 not defined because of singularities) Estimate Std. Error t value Pr(>|t|) (Intercept) 6.5282000 0.7912553 8.250 4.64e-14 *** df$var1 0.0005589 0.0003627 1.541 0.1252 df$var2 -0.2057033 0.0314158 -6.548 6.99e-10 *** df$var3 0.0565537 0.0273348 2.069 0.0401 * fact1a:fact2a NA NA NA NA fact1b:fact2a -0.0086776 1.1375463 -0.008 0.9939 fact15c:fact2a 0.7215114 1.6043880 0.450 0.6535 fact1a:fact2b -1.3091987 0.8251966 -1.587 0.1145 fact1b:fact2b 0.2389941 0.3690889 0.648 0.5182 fact1c:fact2b 0.5016906 0.3474390 1.444 0.1506 fact1a:fact2c NA NA NA NA fact1b:fact2c 0.3121082 0.3491911 0.894 0.3727 fact1c:fact2c NA NA NA NA --- Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 Residual standard error: 1.562 on 166 degrees of freedom Multiple R-squared: 0.3526, Adjusted R-squared: 0.3175 F-statistic: 10.04 on 9 and 166 DF, p-value: 2.952e-12 Should a, b, and c in the factors have the same number of entries? Thanks, u...@host.com -- View this message in context: http://r.789695.n4.nabble.com/lm-interaction-factors-same-number-of-items-per-level-in-factors-tp3341016p3341016.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.