Warning message 'newdata' had 1 row but va

Question

I am suppose to use the predict function to predict when fjbjor is 5.5 and I always get this warning message and I have tried many ways but it always comes so is there anyone who can see what I am doing wrong here

This is my code

fit.lm <- lm(fjbjor~amagn, data=bjor)
summary(fit.lm)

new.bjor<- data.frame(fjbjor=5.5)
predict(fit.lm,new.bjor)

and this comes out

 1        2        3        4        5        6        7        8        9       10       11 
5.981287 2.864521 9.988559 5.758661 4.645530 2.419269 4.645530 5.313409 6.871792 3.309773 4.200278 

      12       13       14       15       16 
3.755026 5.981287 5.536035 1.974016 3.755026  

Warning message: 'newdata' had 1 row but variables found have 16 rows

If anyone can see what is wrong I would be really thankful for the help.

Answer 1

Your model is fjbjor ~ amagn, where fjbjor is response and amagn is covariate. Then your newdata is data.frame(fjbjor=5.5).

newdata should be used to provide covariates rather than response. predict will only retain columns of covariates in newdata. For your specified newdata, this will be NULL. As a result, predict will use the internal model frame for prediction, which returns you fitted values.

The warning message is fairly clear. predict determines the expected number of predictions from nrow(newdata), which is 1. But then what I described above happened so 16 fitted values are returned. Such mismatch produces the warning.

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Looks like the model you really want is: amagn ~ fjbjor.