1. Problem Definition or Opportunity Statement:
To use SPC process capability and control charts to evaluate OUT OF CONTROL analysis of activity duration data points and the process used to calculate them.
Following Dr. Paul D. Giammalvo instructions on my W14 blog post at http://bistro12.blogspot.com/2013/03/w14reginald-nwachukwudetermining.html#comment-form
it is required to evaluate the determined activity durations and the process used to calculate them using the Statistical Process Control. SPC measures both process CAPABILITY and CONTROL using CONTROL CHARTS and PROCESS CAPABILITY tools an techniques.
2. Development of Feasible Alternatives:The variability associated with determining actual activity durations for large construction projects make it a daunting task and requires a concerted efforts from the project scheduler. To apply SPC to the data points available (unconstrained activity duration), the following options may be developed for this analysis.
(i) Historical Duration Data
(ii) Unconstrained Activity Duration
3. Development of Outcome for Each Alternative:
The development of outcome for each alternative will require the scheduler critical skills and understanding and use of SPC control charts and process capability indices to analyse data (both attribute and value or variable data). To this end the outcome for alternatives will strictly be based on the outcomes of the statistical processes applied to the data points. Hence, the TYPE of CONTROL CHART selected is based on the data type (Attribute or Variables) and sample number (n).
(i) Develop control charts using X and R Chart, X and s Chart
(ii) Calculate Process Capability Indices Cp Cr, Cpl Cpu, Cpk
(iii) Analyse and describe the results obtained.
4. Selection of the Acceptable Criteria:
To examine is there any internal causes for an out of control situation, Brassard and Ritter state a process is said to be “out of control” if either one of these below is true:
1. One or more points fall outside the control limits (outside + 3 Sigma and – 3 Sigma)
2. Two points, out of three consecutive points, are on the same side of the average between + 2 Sigma and + 3 Sigma, between – 2 Sigma and – 3 Sigma, or beyond
3. Four points, out of five consecutive points, are on the same side of the average between + 1 Sigma and + 2 Sigma, between – 1 Sigma and – 2 Sigma, or beyond
4. Nine consecutive points are on the same side of average
5. There are six consecutive points, increasing or decreasing
6. There are 14 consecutive points that alternate up and down
7. There are 15 consecutive points between mean and + 1 Sigma and mean and – 1 Sigma
To examine is there any process causes for an out of control situation, Brassard and Ritter state a process capability is to determine whether a process, given its natural variation, is capable of meeting established customer requirements or specifications.
Process Capability Ratio (Cp)
5. Analysis and Comparison of Each Alternative:From results obtained from the development of outcome from each alternatives; the control charts showed data point that were OUT OF CONTROL. This could be due to workload factor and workhours assumed for calculation of Ordinary Duration (OD) data point. This will be revise to reflect the expected duration based on work hours
6. Selection of Preferred Alternative:The Control charts - X-Dbl bar and R-Bar and X-Dbl Bar and s-Bar charts were used to identify data points (Activity Durations) that are OUT OF CONTROL, whereas the Process Capability was used to establish that the process used to obtain data points is not flawed and that the process is capable at a value of 1.
7. Performance Monitoring and Evaluation of Results:The control charts and the process capability method are valuable tools that can be employed by project teams and project controls to monitor the boundary of their data points collected and recorded while carrying out their daily activities or implementing projects.
1. AACE International (2012) Skills and Knowledge of Cost Engineering (5th Edition Revised) pp. 28.3-28.7 AACE International Morgantown W.V.
2. Brassard, M. & Ritter, D.(2010). The Memory Jogger 2: Tools for Continuous Improvement and Effective Planning, pp.53-70,173-177,182-187
3. AACE International (2008) Planning and Scheduling Professional certification Guide (First Edition Revised) pp. 143-145 AACE International Morgantown W.V.
4. AACE International Recommended Practice No. 49R-06 (2012) Determining Activity Duration pp. 1 - 12 AACE International Morgantown W.V