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Cover image for Statistics Day 3: Understanding P-Value — The Heart of Hypothesis Testing
Chanchal Singh
Chanchal Singh

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Statistics Day 3: Understanding P-Value — The Heart of Hypothesis Testing

Have you ever tried to prove a point to your friends?
Maybe you said — “I think this coin is magic! It always lands on heads!”

Your friends would say — “Really? Let’s test it!”

That’s kind of how data scientists use P-Value — to check if something is truly special or just luck.


Step 1: The Simple Idea

P-Value helps us decide whether what we see in data is real or just a coincidence.

Let’s say you flip a coin 10 times.
It lands on heads 9 times. 😮

Now you wonder — “Is this coin really unfair, or did I just get lucky?”

That’s when P-Value comes in.

evaluating p-value using coin tossing


Step 2: How P-Value Works

Imagine a little helper called P-Val, who whispers to you how “surprising” your result is.

If your coin result is... P-Val says... What it means
Very normal (like 5 heads, 5 tails) “That’s common!” Nothing special here
A bit unusual (like 7 heads, 3 tails) “Hmm, slightly surprising.” Could be luck
Super weird (like 9 heads, 1 tail) “Whoa! That’s rare!” Maybe the coin is unfair

So, the smaller the P-Value, the more unusual your result is — and the more likely you’ve found something real!


Step 3: The Magic Number — 0.05

Scientists often use 0.05 (5%) as a magic line.

P-Value What We Decide
Less than 0.05 “Wow! Probably something real happening here!”
More than 0.05 “Hmm, might just be luck.”

So if your P-Value is 0.03, you’d say —
👉 “This is rare! Maybe my coin is really unfair.”

But if it’s 0.20, you’d say —
👉 “That’s not rare enough. Probably just chance.”

p-vlaue description


Step 4: In Technical Terms

Null Hypothesis (H₀) = Nothing special happening.

Alternative Hypothesis (H₁) = Something special happening.

P-Value tells us how likely our data would be if H₀ (nothing special) was actually true.

So when P-Value is tiny, it means our result is too rare to be just chance, so we reject H₀.


Step 5: Real-Life Example

Let’s say a company says —
“Our new cookie recipe makes people 10% happier!” 🍪😁

We test it on 100 people.
If the P-Value comes out less than 0.05, it means —
→ The happiness difference is real, not just random luck.

If it’s higher than 0.05,
→ Maybe the cookies are tasty… but not that special. 😅

p-value demonstration by graph


TL;DR

P-Value Tells how surprising your result is
Small P-Value (< 0.05) Rare → probably something real
Big P-Value (> 0.05) Common → probably just luck
Helps with Deciding if your finding is real or coincidence


🧭 Final Thought

Think of P-Value like a surprise meter.
It doesn’t prove anything 100%, but it helps you know whether your data is whispering “hey, look deeper!” or “nah, just a coincidence.”


I love breaking down complex topics into simple, easy-to-understand explanations so everyone can follow along. If you're into learning AI in a beginner-friendly way, make sure to follow for more!

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