Industrial Engineering - PERFORMANCE RATING AND RELATED TOPICS

PERFORMANCE RATING

PERFORMANCE RATING

DURING THE TIME STUDY, TIME STUDY ENGINEER CAREFULLY OBSERVES THE PERFORMANCE OF THE OPERATOR. THIS PERFORMANCE SELDOM CONFORMS TO THE EXACT DEFINITION OF NORMAL OR STANDARD. THEREFORE, IT BECOMES NECESSARY TO APPLY SOME 'ADJUSTMENT' TO THE MEAN OBSERVED TIME TO ARRIVE AT THE TIME THAT THE NORMAL OPERATOR WOULD HAVE TAKEN TO DO THAT JOB WHEN WORKING AT AN AVERAGE PACE. THIS 'ADJUSTMENT' IS CALLED PERFORMANCE RATING.

DETERMINATION OF PERFORMANCE RATING IS AN IMPORTANT STEP IN THE WORK MEASUREMENT PROCEDURE. IT IS BASED ENTIRELY ON THE EXPERIENCE, TRAINING, AND JUDGMENT OF THE WORK-STUDY ENGINEER. IT IS THE STEP MOST SUBJECTIVE AND THEREFORE IS SUBJECT TO CRITICISM.

PERFORMANCE RATING CAN BE DEFINED AS THE PROCEDURE IN WHICH THE TIME STUDY ENGINEER COMPARES THE PERFORMANCE OF OPERATOR(S) UNDER OBSERVATION TO THE NORMAL PERFORMANCE AND DETERMINES A FACTOR CALLED RATING FACTOR.

SYSTEM OF RATING

THERE ARE SEVERAL SYSTEMS OF RATING THE PERFORMANCE OF OPERATOR ON A JOB.

THESE ARE:

•  PACE RATING

•  WESTINGHOUSE SYSTEM OF RATING

•  OBJECTIVE RATING

•  SYNTHETIC RATING

A BRIEF DESCRIPTION OF EACH RATING METHOD FOLLOWS.

PACE RATING

UNDER THIS SYSTEM, OPERATOR'S PERFORMANCE IS EVALUATED BY CONSIDERING HIS RATE OF ACCOMPLISHMENT OF THE WORK. THE STUDY PERSON MEASURES THE EFFECTIVENESS OF THE OPERATOR AGAINST THE CONCEPT OF NORMAL PERFORMANCE AND THEN ASSIGNS A PERCENTAGE TO INDICATE THE RATIO OF THE OBSERVED PERFORMANCE TO NORMAL OR STANDARD PERFORMANCE.

IN THIS METHOD, WHICH IS ALSO CALLED THE SPEED RATING METHOD, THE TIME STUDY PERSON JUDGES THE OPERATORS SPEED OF MOVEMENTS, I.E. THE RATE AT WHICH HE IS APPLYING HIMSELF, OR IN OTHER WORDS "HOW FAST" THE OPERATOR PERFORMS THE MOTIONS INVOLVED.

WESTINGHOUSE SYSTEM OF RATING

THIS METHOD CONSIDERS FOUR FACTORS IN EVALUATING THE PERFORMANCE OF OPERATOR: SKILL, EFFORT, CONDITIONS, AND CONSISTENCY.

SKILL MAY BE DEFINED AS THE PROFICIENCY AT OF AN INDIVIDUAL IN FOLLOWING THE GIVEN METHOD. IT IS DEMONSTRATED BY CO-ORDINATION OF MIND AND HANDS. A PERSON'S SKILL IN A GIVEN OPERATION INCREASES WITH HIS EXPERIENCE ON THE JOB, BECAUSE INCREASED FAMILIARITY WITH WORK BRINGS SPEED, SMOOTHNESS OF MOTIONS AND FREEDOM FROM HESITATIONS.

THE WESTINGHOUSE SYSTEM LISTS SIX CLASSES OF EACH FACTOR. FOR INSTANCE THE CLASSES OF SKILL ARE POOR, FAIR, AVERAGE, GOOD, EXCELLENT AND SUPERSKILL, AS GIVEN IN A TABLE .

WORK SAMPLING

WORK SAMPLING

WORK SAMPLING (ALSO SOMETIMES CALLED RATIO DELAY STUDY) IS A TECHNIQUE OF GETTING FACTS ABOUT UTILIZATION OF MACHINES OR HUMAN BEINGS THROUGH A LARGE NUMBER OF INSTANTANEOUS OBSERVATIONS TAKEN AT RANDOM TIME INTERVALS. THE RATIO OF OBSERVATIONS OF A GIVEN ACTIVITY TO THE TOTAL OBSERVATIONS APPROXIMATES THE PERCENTAGE OF TIME THAT THE PROCESS IS IN THAT STATE OF ACTIVITY. FOR EXAMPLE, IF 500 INSTANTANEOUS OBSERVATIONS TAKEN AT RANDOM INTERVALS OVER A FEW WEEKS SHOW THAT A LATHE OPERATOR WAS DOING PRODUCTIVE WORK IN 365 OBSERVATIONS AND IN THE REMAINING 135 OBSERVATIONS HE WAS FOUND 'IDLE' FOR MISCELLANEOUS REASONS, THEN IT CAN BE RELIABLY TAKEN THAT THE OPERATOR REMAINS IDLE (135/500) X 100 = 27 % 0F THE TIME. OBVIOUSLY, THE ACCURACY OF THE RESULT DEPENDS ON THE NUMBER OF OBSERVATIONS. HOWEVER, IN MOST APPLICATIONS THERE IS USUALLY A LIMIT BEYOND WHICH GREATER ACCURACY OF DATA IS NOT ECONOMICALLY WORTHWHILE.

USE OF WORK SAMPLING FOR STANDARD TIME DETERMINATION
WORK SAMPLING CAN BE VERY USEFUL FOR ESTABLISHING TIME STANDARDS ON BOTH DIRECT AND INDIRECT LABOR JOBS. THE PROCEDURE FOR CONDUCTING WORK SAMPLING STUDY FOR DETERMINING STANDARD TIME OF A JOB CAN BE DESCRIBED STEP-WISE. 

STEP 1 . DEFINE THE PROBLEM.

•  DESCRIBE THE JOB FOR WHICH THE STANDARD TIME IS TO BE DETERMINED.

•  UNAMBIGUOUSLY STATE AND DISCRIMINATE BETWEEN THE TWO CLASSES OF ACTIVITIES OF OPERATOR ON THE JOB: WHAT ARE THE ACTIVITIES OF JOB THAT WOULD ENTITLE HIM TO BE IN 'WORKING" STATE.

THIS WOULD IMPLY THAT WHEN OPERATOR WILL BE FOUND ENGAGED IN ANY ACTIVITY OTHER THAN THOSE WOULD ENTITLE HIM TO BE IN "NOT WORKING" STATE. 

STEP 2. DESIGN THE SAMPLING PLAN.

•  ESTIMATE SATISFACTORY NUMBER OF OBSERVATIONS TO BE MADE.

•  DECIDE ON THE PERIOD OF STUDY, E.G. TWO DAYS, ONE WEEK, ETC.

•  PREPARE DETAILED PLAN FOR TAKING THE OBSERVATIONS.

THIS WILL INCLUDE OBSERVATION SCHEDULE, EXACT METHOD OF OBSERVING, DESIGN OF OBSERVATION SHEET, ROUTE TO BE FOLLOWED, PARTICULAR PERSON TO BE OBSERVED AT THE OBSERVATION TIME, ETC.

STEP 3. CONTACT THE PERSONS CONCERNED AND TAKE THEM IN CONFIDENCE REGARDING CONDUCT OF THE STUDY.

STEP 4. MAKE THE OBSERVATIONS AT THE PRE-DECIDED RANDOM TIMES ABOUT THE WORKING / NOT WORKING STATE OF THE OPERATOR. WHEN OPERATOR IS IN WORKING STATE, DETERMINE HIS PERFORMANCE RATING. RECORD BOTH ON THE OBSERVATION SHEET.

STEP 5. OBTAIN AND RECORD OTHER INFORMATION. THIS INCLUDES OPERATOR'S STARTING TIME AND QUITTING TIME OF THE DAY AND TOTAL NUMBER OF PARTS OF ACCEPTABLE QUALITY PRODUCED DURING THE DAY.

STEP 6. CALCULATE THE STANDARD TIME PER PIECE.

WE WILL NOW BRIEFLY DISCUSS SOME IMPORTANT ISSUES INVOLVED IN THE PROCEDURE.

NUMBER OF OBSERVATIONS
AS WE KNOW, RESULTS OF STUDY BASED ON LARGER NUMBER OF OBSERVATIONS ARE MORE ACCURATE, BUT TAKING MORE AND MORE OBSERVATIONS CONSUMES TIME AND THUS IS COSTLY. A COST-BENEFIT TRADE-OFF HAS THUS TO BE STRUCK. IN PRACTICE, THE FOLLOWING METHODS ARE USED FOR ESTIMATION OF THE NUMBER OF OBSERVATIONS TO BE MADE. 

(I) BASED ON JUDGMENT. THE STUDY PERSON CAN DECIDE THE NECESSARY NUMBER OF OBSERVATIONS BASED ON HIS JUDGMENT. THE CORRECTNESS OF THE NUMBER MAY BE IN DOUBT BUT ESTIMATE IS OFTEN QUICK AND IN MANY CASES ADEQUATE.

(II) USING CUMULATIVE PLOT OF RESULTS. AS THE STUDY PROGRESSES THE RESULTS OF THE PROPORTION OF TIME DEVOTED TO THE GIVEN STATE OR ACTIVITY, I.E. PI FROM THE CUMULATIVE NUMBER OF OBSERVATIONS ARE PLOTTED AT THE END OF EACH SHIFT OR DAY. A TYPICAL PLOT IS SHOWN IN FIGURE. 

SINCE THE ACCURACY OF THE RESULT IMPROVES WITH INCREASING NUMBER OF OBSERVATIONS, THE STUDY CAN BE CONTINUED UNTIL THE CUMULATIVE PI APPEARS TO STABILIZE AND COLLECTION OF FURTHER DATA SEEMS TO HAVE NEGLIGIBLE EFFECT ON THE VALUE OF PI.

(III) USE OF STATISTICS. IN THIS METHOD, BY CONSIDERING THE IMPORTANCE OF THE DECISION TO BE BASED ON THE RESULTS OF STUDY, A MAXIMUM TOLERABLE SAMPLING ERROR IN TERMS OF CONFIDENCE LEVEL AND DESIRED ACCURACY IN THE RESULTS IS SPECIFIED. A PILOT STUDY IS THEN MADE IN WHICH A FEW OBSERVATIONS ARE TAKEN TO OBTAIN A PRELIMINARY ESTIMATE OF PI. THE NUMBER OF OBSERVATIONS N NECESSARY ARE THEN CALCULATED USING THE FOLLOWING EXPRESSION.

THE NUMBER OF OBSERVATIONS ESTIMATED FROM THE ABOVE RELATION USING A VALUE OF PI OBTAINED FROM A PRELIMINARY STUDY WOULD BE ONLY A FIRST ESTIMATE. IN ACTUAL PRACTICE, AS THE WORK SAMPLING STUDY PROCEEDS, SAY AT THE END OF EACH DAY, A NEW CALCULATION SHOULD BE MADE BY USING INCREASINGLY RELIABLE VALUE OF PI OBTAINED FROM THE CUMULATIVE NUMBER OF OBSERVATIONS MADE.

DETERMINATION OF OBSERVATION SCHEDULE

THE NUMBER OF INSTANTANEOUS OBSERVATIONS TO BE MADE EACH DAY MAINLY DEPENDS UPON THE NATURE OF OPERATION. FOR EXAMPLE, FOR NON-REPETITIVE OPERATIONS OR FOR OPERATIONS IN WHICH SOME ELEMENTS OCCUR IN-FREQUENTLY, IT IS ADVISABLE TO TAKE OBSERVATIONS MORE FREQUENTLY SO THAT THE CHANCE OF OBTAINING ALL THE FACTS IMPROVES. IT ALSO DEPENDS ON THE AVAILABILITY OF TIME WITH THE PERSON MAKING THE STUDY. IN GENERAL, ABOUT 50 OBSERVATIONS PER DAY IS A GOOD FIGURE. THE ACTUAL RANDOM SCHEDULE OF THE OBSERVATIONS IS PREPARED BY USING RANDOM NUMBER TABLE OR ANY OTHER TECHNIQUE.

EXAMPLE

A WORK SAMPLING STUDY WAS MADE OF A CARGO LOADING OPERATION FOR THE PURPOSE OF DEVELOPING ITS STANDARD TIME. THE STUDY WAS CONDUCTED FOR DURATION OF 1500 MINUTES DURING WHICH 300 INSTANTANEOUS OBSERVATIONS WERE MADE AT RANDOM INTERVALS. THE RESULTS OF STUDY INDICATED THAT THE WORKER ON THE JOB WAS WORKING 80 PERCENT OF THE TIME AND LOADED 360 PIECES OF CARGO DURING THE STUDY PERIOD. THE WORK ANALYST RATED THE PERFORMANCE AT 90 %. IF THE MANAGEMENT WISHES TO PERMIT A 13 % ALLOWANCE FOR FATIGUE, DELAYS AND PERSONAL TIME, WHAT IS THE STANDARD TIME OF THIS OPERATION?

ANS:

HERE, TOTAL STUDY PERIOD = 1500 MINUTES

WORKING FRACTION = 80 PERCENT

AVERAGE RATING = 90 PERCENT

NUMBER OF UNITS LOADED = 360

ALLOWANCES = 13 %

ADVANTAGES AND DISADVANTAGES OF WORK SAMPLING IN COMPARISON WITH TIME STUDY.

ADVANTAGES

ECONOMICAL

• MANY OPERATORS OR ACTIVITIES WHICH ARE DIFFICULT OR UNECONOMICAL TO MEASURE BY TIME STUDY CAN READILY BE MEASURED BY WORK SAMPLING.
• TWO OR MORE STUDIES CAN BE SIMULTANEOUSLY MADE OF SEVERAL OPERATORS OR MACHINES BY A SINGLE STUDY PERSON. ORDINARILY A WORK STUDY ENGINEER CAN STUDY ONLY ONE OPERATOR AT A TIME WHEN CONTINUOUS TIME STUDY IS MADE.
• IT USUALLY REQUIRES FEWER MAN-HOURS TO MAKE A WORK SAMPLING STUDY THAN TO MAKE A CONTINUOUS TIME STUDY. THE COST MAY ALSO BE ABOUT A THIRD OF THE COST OF A CONTINUOUS TIME STUDY.
• NO STOPWATCH OR OTHER TIME MEASURING DEVICE IS NEEDED FOR WORK SAMPLING STUDIES.
• IT USUALLY REQUIRES LESS TIME TO CALCULATE THE RESULTS OF WORK SAMPLING STUDY. MARK SENSING CARDS MAY BE USED WHICH CAN BE FED DIRECTLY TO THE COMPUTING MACHINES TO OBTAIN THE RESULTS JUST INSTANTANEOUSLY.

FLEXIBLE

• A WORK SAMPLING STUDY MAY BE INTERRUPTED AT ANY TIME WITHOUT AFFECTING THE RESULTS.
• OPERATORS ARE NOT CLOSELY WATCHED FOR LONG PERIOD OF TIME. THIS DECREASES THE CHANCE OF GETTING ERRONEOUS RESULTS FOR WHEN A WORKER IS OBSERVED CONTINUOUSLY FOR A LONG PERIOD, IT IS PROBABLE THAT HE WILL NOT FOLLOW HIS USUAL ROUTINE EXACTLY DURING THAT PERIOD.

LESS ERRONEOUS

• OBSERVATIONS MAY BE TAKEN OVER A PERIOD OF DAYS OR WEEKS. THIS DECREASES THE CHANCE OF DAY-TO-DAY OR WEEK-TO-WEEK VARIATIONS THAT MAY AFFECT THE RESULTS.

OPERATORS LIKE IT

• WORK SAMPLING STUDIES ARE PREFERRED TO CONTINUOUS TIME STUDY BY THE OPERATORS BEING STUDIED. SOME PEOPLE DO NOT LIKE TO BE OBSERVED CONTINUOUSLY FOR LONG PERIODS OF TIME.

OBSERVERS LIKE IT

• WORK SAMPLING STUDIES ARE LESS FATIGUING AND LESS TEDIOUS TO MAKE ON THE PART OF TIME STUDY ENGINEER.

DISADVANTAGES

• WORK SAMPLING IS NOT ECONOMICAL FOR THE STUDY OF A SINGLE OPERATOR OR OPERATION OR MACHINE. ALSO, WORK-SAMPLING STUDY MAY BE UNECONOMICAL FOR STUDYING OPERATORS OR MACHINES LOCATED OVER WIDE AREAS.
• WORK SAMPLING STUDY DOES NOT PROVIDE ELEMENTAL TIME DATA.
• THE OPERATOR MAY CHANGE HIS WORK PATTERN WHEN HE SEES THE STUDY PERSON. FOR INSTANCE, HE MAY TRY TO LOOK PRODUCTIVE AND MAKE THE RESULTS OF STUDY ERRONEOUS.
• NO RECORD IS USUALLY MADE OF THE METHOD BEING USED BY THE OPERATOR. THEREFORE, A NEW STUDY HAS TO BE MADE WHEN A METHOD CHANGE OCCURS IN ANY ELEMENT OF OPERATION.
• COMPARED TO STOP WATCH TIME STUDY, THE STATISTICAL APPROACH OF WORK SAMPLING STUDY IS DIFFICULT TO UNDERSTAND BY WORKERS.

COMPUTERIZED WORK SAMPLING

USE OF A COMPUTER CAN SAVE AS MUCH AS 30 TO 40 PERCENT OF THE TOTAL WORK SAMPLING STUDY COST. THIS IS BECAUSE TOO MUCH CLERICAL EFFORT IS INVOLVED IN SUMMARIZING WORK SAMPLING DATA, E.G. IN DETERMINING THE NUMBER OF OBSERVATIONS REQUIRED, DETERMINING THE DAILY OBSERVATIONS REQUIRED, DETERMINING THE NUMBER OF TRIPS TO THE AREA BEING STUDIED PER DAY, DETERMINING THE TIME OF EACH OBSERVATION, CALCULATING THE ACCURACY OF RESULTS, PLOTTING DATA ON CONTROL CHARTS AND LIKE THAT. COMPUTERS CAN BE USED FOR MECHANIZATION OF THE REPETITIVE CALCULATIONS, DISPLAY OF CONTROL CHARTS AND CALCULATION OF DAILY AS WELL AS CUMULATIVE RESULTS. 

References:-   www.nptel.iitm.ac.in/