谢谢指点，用R做面板模型分析时遇到了如下问题，为什么会缺一个变量而且没有截距，mp表示货币供给量的增长率这是代码
aa <- lev~fin+owe+Growth+KZ+mp+log(Assets)+ro+ro*fin
random <- plm(aa,data=good,index=c("Symbol","Enddate"),effect="time",model="within")
这是运行结果，没有mp的结果
summary(random)

Call:
plm(formula = aa, data = good, effect = "time", model = "within",
    index = c("Symbol", "Enddate"))

Unbalanced Panel: n = 2850, T = 1-11, N = 12950

Residuals:
     Min.   1st Qu.    Median   3rd Qu.      Max.
-0.511811 -0.113601 -0.014425  0.100795  0.727313

Coefficients:
              Estimate Std. Error  t-value  Pr(>|t|)   
fin         -0.4311793  0.0106665 -40.4236 < 2.2e-16 ***
owe          0.0435280  0.0032303  13.4748 < 2.2e-16 ***
Growth       0.0092864  0.0062243   1.4920 0.1357364   
KZ           0.0165505  0.0013974  11.8439 < 2.2e-16 ***
log(Assets)  0.0780930  0.0016018  48.7547 < 2.2e-16 ***
ro           0.0026172  0.0035745   0.7322 0.4640645   
fin:ro       0.0338672  0.0102182   3.3144 0.0009209 ***
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

Total Sum of Squares:    499.1
Residual Sum of Squares: 333.07
R-Squared:      0.33267
Adj. R-Squared: 0.33179
F-statistic: 920.942 on 7 and 12932 DF, p-value: < 2.22e-16