2.5 



SCRIPPS PIER • 

 TRIPLE ISLAND o 



.2 .3 .4 .5 



FRACTION OF DATA MISSING 



Figure 9. Fractional increase 

 in variance of regression 

 coefficients due to nonrandom 

 missing data. 



|S's attributable to nonrandom missing data is twice the in- 

 crease attributable to random missing data. This suggests 

 caution in estimating the variances of /3's, or of residuals, 

 for time series when the missing data occurs in sequences 

 longer than those occurring by chance. 



28 



