[R] Error of Stepwise Regression with number of rows in use has changed: remove missing values?

[Kum-Hoe Hwang]

Howdy, R Grues

I have enjoyed R, but I cannot solve one problem easily. Please help my problem.
When I tried the R script, I got the following Error. This error
results from input data file exported through a Excel spreadsheet
software.

 Error in step(lm(pop.rate ~ as.numeric(year) + as.factor(policy) +
as.numeric(nation.grant) +  :
  number of rows in use has changed: remove missing values?

Could you direct me to solve the Error?
Thanks in advance,


> ############### outputs from R console ###############
> pop <- step(
+             lm(pop.rate ~ as.numeric(year) + as.factor(policy) +
as.numeric(nation.grant)
+                + as.numeric(do.grant) + as.numeric(city.grant) +
as.numeric(DMZ.dist) + as.numeric(Seoul.dist), data=borderI.data,
na.action = na.omit)
+             )
Start:  AIC=494.27
pop.rate ~ as.numeric(year) + as.factor(policy) + as.numeric(nation.grant) +
    as.numeric(do.grant) + as.numeric(city.grant) + as.numeric(DMZ.dist) +
    as.numeric(Seoul.dist)
                           Df Sum of Sq    RSS    AIC
- as.numeric(do.grant)      1      0.71 6622.9 492.28
- as.factor(policy)         1      1.21 6623.4 492.29
- as.numeric(DMZ.dist)      1      1.91 6624.1 492.30
- as.numeric(city.grant)    1      5.07 6627.3 492.36
- as.numeric(nation.grant)  1     11.51 6633.7 492.47
- as.numeric(year)          1     29.58 6651.8 492.80
<none>                                  6622.2 494.27
- as.numeric(Seoul.dist)    1    673.22 7295.4 503.79
Step:  AIC=492.28
pop.rate ~ as.numeric(year) + as.factor(policy) + as.numeric(nation.grant) +
    as.numeric(city.grant) + as.numeric(DMZ.dist) + as.numeric(Seoul.dist)
                           Df Sum of Sq    RSS    AIC
- as.factor(policy)         1      1.99 6624.9 490.32
- as.numeric(DMZ.dist)      1      2.09 6625.0 490.32
- as.numeric(city.grant)    1      7.18 6630.1 490.41
- as.numeric(nation.grant)  1     20.08 6643.0 490.64
- as.numeric(year)          1     28.89 6651.8 490.80
<none>                                  6622.9 492.28
- as.numeric(Seoul.dist)    1    697.46 7320.4 502.20
Step:  AIC=490.32
pop.rate ~ as.numeric(year) + as.numeric(nation.grant) +
as.numeric(city.grant) +
    as.numeric(DMZ.dist) + as.numeric(Seoul.dist)
                           Df Sum of Sq    RSS    AIC
- as.numeric(DMZ.dist)      1      2.08 6627.0 488.35
- as.numeric(city.grant)    1     10.65 6635.6 488.51
- as.numeric(nation.grant)  1     31.30 6656.2 488.88
- as.numeric(year)          1     31.44 6656.4 488.88
<none>                                  6624.9 490.32
- as.numeric(Seoul.dist)    1    732.88 7357.8 500.80
Step:  AIC=488.35
pop.rate ~ as.numeric(year) + as.numeric(nation.grant) +
as.numeric(city.grant) +
    as.numeric(Seoul.dist)
                           Df Sum of Sq    RSS    AIC
- as.numeric(city.grant)    1      9.86 6636.9 486.53
- as.numeric(year)          1     31.42 6658.4 486.92
- as.numeric(nation.grant)  1     33.33 6660.3 486.95
<none>                                  6627.0 488.35
- as.numeric(Seoul.dist)    1    754.40 7381.4 499.18

Error in step(lm(pop.rate ~ as.numeric(year) + as.factor(policy) +
as.numeric(nation.grant) +  :
-------------------------------------------------------------------------------------------------------------------------------------------
  number of rows in use has changed: remove missing values?
------------------------------------------------------------------------------------------




--
Kum-Hoe Hwang, Ph.D.

Phone : 82-31-250-3516
Email : phdhwang at gmail.com