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SUBROUTINE SRATE

PURPOSE
   TO COMPUTE THE PROPORTION OF SUBJECTS SURVIVING, THE
   SURVIVAL RATES AND THE STANDARD ERRORS FOR SUCCESSIVELY
   REDUCED TIME PERIODS.  THE SURVIVAL RATE IS COMPUTED FOR
   EACH OF K PERIODS, WHERE K IS A CONSTANT TO BE SPECIFIED AND
   IS LESS THAN OR EQUAL TO N (WHERE N = TOTAL NUMBER OF
   PERIODS).

USAGE
   CALL SRATE (N,K,X,IE)

DESCRIPTION OF PARAMETERS
   N - THE TOTAL NUMBER OF PERIODS AFTER TREATMENT OR DIAGNOSIS
   K - THE SPECIFIED PERIOD UP TO WHICH SURVIVAL RATES ARE TO
       BE CALCULATED
   X - AN INPUT AND OUTPUT MATRIX (N X 9) CONTAINING THE
       FOLLOWING INFORMATION
       FOR INPUT--STORED IN THE N ROWS OF EACH COLUMN
	  COL 1 - NUMBER OF SUBJECTS ALIVE AT THE BEGINNING OF
		  PERIOD
	  COL 2 - NUMBER OF SUBJECTS WHICH DIED DURING THE
		  PERIOD
	  COL 3 - NUMBER OF SUBJECTS LOST TO FOLLOW-UP DURING
		  THE PERIOD
	  COL 4 - NUMBER OF SUBJECTS WITHDRAWN ALIVE DURING THE
		  PERIOD
	    FOR OUTPUT--STORED IN THE FIRST K ROWS OF EACH
	    COLUMN
	  COL 5 - EFFECTIVE NUMBER EXPOSED TO THE RISK OF DYING
	  COL 6 - PROPORTION WHO DIED DURING THE PERIOD
	  COL 7 - PROPORTION WHO SURVIVED DURING THE PERIOD
	  COL 8 - SURVIAL RATE
	  COL 9 - STANDARD ERROR OF THE SURVIVAL RATE
   IE- 1, IF K IS NOT IN THE CLOSED INTERVAL (0,N).
       2, IF THE NUMBER OF SUBJECTS ALIVE AT THE BEGINNING
       OF PERIOD I IS LESS THAN THE SUM OF THOSE WHICH DIED,
       WERE LOST, OR WERE WITHDRAWN DURING PERIOD I (I=1,...N)
       3, IF THE NUMBER OF SUBJECTS WHICH DIED, WERE LOST, OR
       WERE WITHDRAWN IN PERIOD I IS NOT EQUAL TO THE NUMBER
       ALIVE AT THE BEGINNING OF PERIOD I LESS THE NUMBER
       ALIVE AT THE BEGINNING OF PERIOD I + 1 (I=1,...N-1)

REMARKS
   IF THE SUBJECTS IN A GIVEN GROUP ARE ALL DIAGNOSED OR
   TREATED AT THE SAME TIME, THE CONSTANT K MAY BE SET EQUAL TO
   N .	IF THE SUBJECTS IN A GIVEN GOUP ENTER THE STUDY AT
   VARYING TIMES, K CAN BE NO GREATER THAN N-1.

SUBROUTINES AND FUNCTION SUBPROGRAMS REQUIRED
   NONE

METHOD
   REFER TO S. J. CUTLER AND F. EDERER 'MAXIMUM UTILIZATION OF
   THE LIFE TABLE METHOD IN ANALYZING SURVIVAL', JOURNAL OF
   CHRONIC DISEASES, DECEMBER, 1958.  PP 699-712.