Project Management and Quality Control
This domain tests schedule logic, progress measurement and statistical process control - can you find the critical path, read earned value, and judge whether a process is capable?
Scheduling and control
- WBS decomposes scope into deliverable work packages; the schedule is built from activity durations and dependencies.
- CPM: the critical path is the longest path through the network, and it sets the project duration. Total float = LS − ES = LF − EF. Activities on the critical path have zero float. A shorter path has float and can slip within it.
- Earned value: CPI = EV/AC measures cost efficiency; SPI = EV/PV measures schedule efficiency. Values below 1.0 indicate overrun or slippage. EAC is typically BAC/CPI when the current trend continues.
- PERT uses three-point estimates to express duration uncertainty.
Quality control
- Seven tools: Pareto, cause-and-effect (fishbone), check sheet, histogram, control chart, scatter diagram, flow chart. Pareto directs effort at the vital few causes.
- Control charts separate common-cause from special-cause variation; only special causes justify intervention.
- Cp = (USL − LSL)/(6σ) measures potential capability. Cpk = min[(USL − x̄)/(3σ), (x̄ − LSL)/(3σ)] measures actual capability and penalises off-centre processes.
- ISO 9001 is a quality management system standard, not a product specification. Six Sigma uses DMAIC.
Worked example
A shaft has limits 9.90 mm and 10.10 mm, process mean 10.02 mm and σ = 0.02 mm. Cpu = (10.10 − 10.02)/(3 × 0.02) = 1.33; Cpl = (10.02 − 9.90)/0.06 = 2.00. Cpk = 1.33. Capable, but a small shift of the mean towards 10.04 would drop Cpk to 1.00, so the process needs centring, not tighter limits.
Traps that cost marks
Calling the shortest path critical. Computing SPI from actual cost instead of planned value. Reporting Cp when the process is off-centre. Reacting to common-cause variation by adjusting the process.