Planning a Statistical Investigation – Procedure & Considerations

"Failing to plan is planning to fail!" - This applies perfectly to statistical investigations. 📋

Why Planning is Crucial

[!IMPORTANT] Proper planning:

• Saves time and money
• Ensures accuracy of results
• Prevents wastage of resources
• Makes investigation systematic

Example: If you plan to survey 10,000 people without proper planning, you might realize later that you asked the wrong questions!

Procedure for Planning

Step 1️⃣: Define the Objective Clearly

Questions to Answer:

• What do we want to find out?
• Why is this investigation needed?
• Who will use the results?

Example:

• ❌ Bad: "Study customer satisfaction"
• ✅ Good: "Measure customer satisfaction scores for our mobile app among users aged 18-35 in metro cities"

Step 2️⃣: Determine the Scope

Define the Boundaries:

graph TD
    A[Scope Definition] --> B[Geographical Area]
    A --> C[Time Period]
    A --> D[Target Population]
    A --> E[Variables to Study]
    
    B --> B1[Mumbai only or All India?]
    C --> C1[Last month or Last year?]
    D --> D1[All citizens or only adults?]
    E --> E1[Age, Income, Education?]

Example:

• Area: Delhi NCR
• Time: January 2024 to March 2024
• Population: Working professionals
• Variables: Monthly income, job satisfaction

Step 3️⃣: Decide on Census vs Sample

Comparison:

Example:

• Census: Population of India (every 10 years)
• Sample: TV rating (TRP) - survey 1000 households, not all households

Step 4️⃣: Determine Sample Size & Sampling Method

Sample Size Factors:

[!NOTE] Larger sample = More accurate but more expensive

Consider:

1. Variability in population (More variety = Larger sample needed)
2. Confidence level required (Higher confidence = Larger sample)
3. Budget available
4. Time available

Sampling Methods:

• Random: Every unit has equal chance (Lottery method)
• Systematic: Every nth unit (Every 10th person)
• Stratified: Divide population into groups first
• Cluster: Divide area into clusters, select few clusters

(Details in Chapter 9)

Step 5️⃣: Design the Questionnaire/Schedule

Good Questionnaire Characteristics:

graph LR
    A[Good Questionnaire] --> B[Clear & Simple]
    A --> C[Unbiased]
    A --> D[Relevant]
    A --> E[Logical Order]
    A --> F[Not Too Long]
    
    B --> B1[Use simple words]
    C --> C1[Avoid leading questions]
    D --> D1[Only necessary questions]
    E --> E1[Easy to difficult]
    F --> F1[Max 15-20 questions]

Examples:

• ❌ Bad: "Don't you think our product is excellent?" (Leading question)
• ✅ Good: "How would you rate our product on a scale of 1-5?"

Step 6️⃣: Choose Data Collection Method

Options:

1. Direct Personal Interview

   • Interviewer meets respondent face-to-face
   • ✅ High response rate, can clarify doubts
   • ❌ Expensive, time-consuming

2. Mailed Questionnaire

   • Send forms by post/email
   • ✅ Cheap, covers wide area
   • ❌ Low response rate (10-20%)

3. Telephone Interview

   • Call respondents
   • ✅ Quick, moderate cost
   • ❌ Cannot show visuals

4. Online Survey

   • Google Forms, SurveyMonkey
   • ✅ Very cheap, instant results
   • ❌ Only internet users respond

Step 7️⃣: Plan for Data Processing

Decide in Advance:

• Software: Excel, SPSS, R, Python?
• Storage: How to maintain records?
• Analysis: Which statistical tools to use?

Step 8️⃣: Budget & Resource Allocation

Cost Estimation:

Resources Needed:

• Human: Investigators, supervisors, data entry operators
• Material: Stationery, computers, vehicle
• Financial: Budget allocation

Step 9️⃣: Pilot Survey (Pre-Test)

[!TIP] Conduct a small trial run before full investigation!

Pilot Survey Benefits:

• Tests if questions are clear
• Estimates response rate
• Identifies practical problems
• Helps improve questionnaire

Example: Survey 50 people before launching full survey of 5000.

Step 🔟: Train the Investigators

Training Topics:

1. How to approach respondents
2. How to ask questions (neutral tone)
3. How to record answers accurately
4. What to do if respondent refuses
5. Ethical guidelines (privacy, honesty)

Common Planning Mistakes to Avoid

[!CAUTION] Frequent Errors:

1. ❌ Vague objective - "Study market" (Too broad!)
2. ❌ Inadequate budget - Underestimating costs
3. ❌ No pilot test - Directly launching full survey
4. ❌ Biased questions - "Isn't our service great?"
5. ❌ Too long questionnaire - 100 questions = people quit!
6. ❌ Wrong sampling - Online survey for studying elderly people

Planning Checklist for Exam

Remember the 10 Ps:

1. ✅ Purpose - Clear objective
2. ✅ Population - Who to study
3. ✅ Period - Time frame
4. ✅ Parameters - What variables
5. ✅ Plan - Census or sample
6. ✅ Probe - Questionnaire design
7. ✅ Procedure - Collection method
8. ✅ Pilot - Pre-test
9. ✅ Personnel - Staff training
10. ✅ Purse - Budget

Summary

• Planning prevents problems - saves time and money.
• Key steps: Objective → Scope → Sample → Questionnaire → Method → Budget → Pilot → Training.
• Always conduct pilot survey before full investigation.
• Good questionnaire = Clear, unbiased, relevant, short.

Exam Tip: Remember the flow - Define → Decide → Design → Deploy! 📊