Measures of Central Tendency – Mean, Median, Mode ➗

🎯 Learning Objectives

By the end of this lesson, you will be able to:
✔ Define Mean, Median, and Mode
✔ Understand their differences and applications
✔ Calculate each measure from a dataset
✔ Know which measure to use in which situation

1️⃣ Introduction

When we have a set of data, we often want to summarize it with a single value that represents the “center” or “average” of the data. These are called measures of central tendency, and the three most common are:
✅ Mean
✅ Median
✅ Mode

2️⃣ Mean (Arithmetic Average)

Definition:

• The sum of all observations divided by the number of observations.

✔ Formula:

✔ Example:
If weights of 5 patients are: 50, 55, 60, 65, 70 kg

✔ Key Features:

• Affected by extreme values (outliers)
• Best for normally distributed data

3️⃣ Median

Definition:

• The middle value when all observations are arranged in ascending or descending order.
• If the number of observations is even → average of the two middle values.

✔ Example:
Data: 50, 55, 60, 65, 70
Median = 60 (middle value)
If data was 50, 55, 60, 65 → Median = (55 + 60)/2 = 57.5

✔ Key Features:

• Not affected by extreme values
• Best for skewed data

4️⃣ Mode

Definition:

• The value that occurs most frequently in the dataset.

✔ Example:
Data: 50, 55, 60, 60, 70
Mode = 60 (appears twice)

✔ Key Features:

• Can have more than one mode (bimodal or multimodal)
• Useful for categorical data

5️⃣ Comparison Table

6️⃣ Clinical Relevance

• Mean: Used in lab reports (e.g., average hemoglobin level in a population).
• Median: Used in income distribution or skewed medical data like hospital stay length.
• Mode: Used for common blood groups or most frequent diagnosis.

7️⃣ Quick Check: Test Your Understanding ✅

Q1: Which measure is most appropriate for skewed data?
a) Mean
b) Median
c) Mode
👉 Answer: b) Median

Q2: The most frequently occurring blood group in a population is an example of:
a) Mean
b) Median
c) Mode
👉 Answer: c) Mode

Q3: Which measure is affected by outliers?
👉 Answer: Mean

✨ Key Takeaways

• Mean: Sum ÷ Number of values (best for normal data, but sensitive to outliers).
• Median: Middle value (best for skewed data).
• Mode: Most frequent value (best for categorical data).