CPM vs PERT

CPM (Critical Path Method)

• Developed in 1957 by DuPont and Remington Rand for industrial projects.
• Uses deterministic time estimates - a single fixed time is assigned to each activity.
• Focuses on time-cost trade-off - it allows crashing of activities by adding resources to reduce duration.
• Best suited for repetitive, well-defined projects where activity durations are known (e.g., construction, manufacturing).
• Identifies the critical path - the longest path through the network that determines the minimum project duration.
• Activities on the critical path have zero float (slack).

PERT (Program Evaluation and Review Technique)

• Developed in 1958 by the U.S. Navy for the Polaris missile project.
• Uses probabilistic time estimates - three time values are assigned to each activity:
  • Optimistic time (to) - best-case scenario
  • Most likely time (tm) - most realistic estimate
  • Pessimistic time (tp) - worst-case scenario
• Expected time is calculated as: te = (to + 4tm + tp) / 6
• Best suited for non-repetitive, research-oriented, or uncertain projects (e.g., R&D, defense).
• Also identifies the critical path but with statistical probability of completion.

Comparison Table

Key Similarity

CPM & PERT - Network Analysis

Network Analysis - Introduction

(a) PERT - Programme Evaluation and Review Technique

• The essence of PERT is to construct an Arrow Diagram - which represents the logical sequence in which events must take place.
• With such a diagram, it is possible to calculate the time by which each activity must be completed and to identify those activities that are critical.
• This technique provides a basic discipline by which all concerned in a project can know what is expected of them and to minimise delays or crises in the implementation of the plan.

1. Aids in planning, scheduling and monitoring the project
2. Allows better communication between various levels of management
3. Identifies potential problems
4. Furnishes continuous, timely progress reports
5. Forms a solid foundation upon which to build an evaluation and checking system

(b) CPM - Critical Path Method

• If any activity along the critical path is delayed, the entire project will be delayed.
• CPM focuses on identifying this critical path within the arrow/network diagram.

Comparison

Key Similarity

Diagnosis of a Case Presenting with Cough for More Than 4 Weeks - NTEP Guidelines

Step 1: Identify as a Presumptive TB Case

"Presumptive TB refers to a patient who presents with symptoms or signs suggestive of TB (previously known as a TB suspect)."

• Cough with or without sputum production
• Blood in sputum (haemoptysis)
• Fever, especially evening rise
• Night sweats
• Significant weight loss
• Chest pain, breathlessness

Step 2: Case-Finding Approach

• The majority of pulmonary TB patients have persistent cough and fever and seek medical advice on their own initiative (over 60%).
• These patients presenting to health facilities with symptoms form the most important group for case-finding.

• A provider-initiated activity to detect TB cases early by active case finding in targeted/vulnerable groups.
• Covers both people who seek health care and those who do not.

Step 3: NTEP-Endorsed Diagnostic Tools

A. Microbiological (Confirmatory) Tests:

• Ziehl-Neelsen (ZN) staining - conventional light microscopy
• Fluorescence staining - using auramine dye
• LED Fluorescence Microscopy (LED FM) - recommended by WHO as superior to conventional ZN; faster and more sensitive

"One positive specimen out of the two is enough to declare a patient as smear positive TB." Two sputum samples are collected - one spot sample and one early morning sample.

• Solid media - Lowenstein-Jensen (LJ) medium (takes weeks)
• Liquid media - MGIT 960, BACTEC, BacT Alert (results in up to 42 days)
• Used mainly for follow-up of DR-TB patients and to detect relapse

• CB-NAAT / GeneXpert (Xpert MTB/RIF)
  • Detects MTB DNA and Rifampicin resistance
  • Results in 90 minutes from unprocessed sputum
  • Preferred for: children, PLHIV, smear-negative cases, extra-pulmonary TB, presumptive DR-TB
  • Established at DTCs, TB units, and medical colleges
• TrueNat
  • A real-time PCR-based NAAT for MTB complex
  • Portable and decentralized
• Line Probe Assay (LPA)
  • First-line LPA: detects resistance to Rifampicin (rpoB) and Isoniazid (katG, inhA)
  • Second-line LPA: detects fluoroquinolone and second-line injectable resistance

B. Supportive (Non-confirmatory) Tools:

• Chest X-ray and other radiological tests
• Tuberculin Skin Test (TST) / Mantoux test
• Interferon Gamma Release Assay (IGRA)
• Histopathology and tissue-based tests

Park cautions: "A negative tuberculin test cannot be relied upon to exclude tuberculosis."

Step 4: Case Classification after Diagnosis

1. Anatomical site - Pulmonary TB (PTB) vs. Extrapulmonary TB (EPTB)
2. History of previous treatment - New / Previously treated
3. Drug resistance - DS-TB / DR-TB
4. HIV status

Summary Flowchart

Cough > 4 weeks
       ↓
Identify as Presumptive TB Case
       ↓
Collect 2 sputum samples
       ↓
Sputum Smear Microscopy (ZN / LED FM)
       ↓
    Smear Positive → Diagnose as PTB (Bacteriologically confirmed)
    Smear Negative → CBNAAT / TrueNat / Chest X-ray
                         ↓
                 MTB detected → Confirm TB
                 MTB not detected + X-ray suggestive → Clinically diagnosed TB