R proramming:

form<-MOP~PE+WOR+RD
pooltest(form, data=well, effect="individual", model="within")

Waning message:

        F statistic
data:  form
F = -0.4676, df1 = 21753, df2 = -5990, p-value = NA
alternative hypothesis: unstability
Warning message:
In pf(q, df1, df2, lower.tail, log.p) : NaNs produced

p值是NA。为什么？是我的数据有问题吗？我的数据行数是15914，其中MOP有4484是零值。是不是这些零值才算不出来的？