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Common Cause – Two Effects

Introduction

In some reasoning questions, both statements may seem related but neither directly causes the other. Instead, both occur because of a shared or common cause. This pattern is essential for identifying indirect relationships where two outcomes stem from a single underlying reason.

Pattern: Common Cause – Two Effects

Pattern

The key concept is: both statements are effects of one common cause that is not directly mentioned in the question.

Step-by-Step Example

Question

1️⃣ The prices of petrol increased.
2️⃣ The cost of transportation rose.

Which of the following correctly represents the relationship?
(A) 1 → Cause; 2 → Effect
(B) 2 → Cause; 1 → Effect
(C) Both are effects of a common cause
(D) Both are independent

Solution

  1. Step 1: Check if one directly causes the other

    The rise in petrol prices and higher transport cost seem related, but one doesn’t directly cause the other.

  2. Step 2: Identify possible hidden reason

    Both may result from an increase in global crude oil prices.

  3. Step 3: Conclude logical type

    Since both effects share the same underlying reason, it’s a Common Cause pattern.

  4. Final Answer:

    Both are effects of a common cause → Option C

  5. Quick Check:

    If crude oil prices stabilize, both petrol and transport costs may fall → confirms shared origin ✅

Quick Variations

1. Two different outcomes may arise from one natural, economic, or policy-based cause.

2. The common cause might be unstated in the question and must be inferred logically.

3. Both statements often happen around the same time due to an external trigger.

Trick to Always Use

  • Look for an invisible third factor that explains both statements.
  • Check if neither statement can logically cause the other.
  • Ask: “Could both happen due to the same outside reason?” - if yes, it’s a common cause pattern.

Summary

Summary

  • Both statements occur because of a shared external reason.
  • Neither statement directly causes the other.
  • Identify the hidden or implied factor connecting both.
  • Used in economy, environment, and policy-based reasoning questions.

Example to remember:
“Petrol price rise” and “Transport cost rise” → Both effects of crude oil price increase.

Practice

(1/5)
1. 1️⃣ The number of people suffering from cough and cold increased. 2️⃣ The sale of cold medicines went up sharply. Identify the correct cause-effect relationship.
easy
A. 1 → Cause; 2 → Effect
B. 2 → Cause; 1 → Effect
C. Both are effects of a common cause
D. Both are independent

Solution

  1. Step 1: Check if one causes the other

    Higher cold medicine sales and more people catching colds occur together but not directly due to each other.

  2. Step 2: Identify possible shared reason

    Both could be caused by a sudden change in weather.

  3. Step 3: Conclude

    Both statements are effects of the same cause - cold weather.

  4. Final Answer:

    Both are effects of a common cause → Option C

  5. Quick Check:

    If weather improves, both effects reduce → shared cause confirmed ✅
Hint: Look for an unseen event (like weather) that explains both outcomes.
Common Mistakes: Assuming medicine sales caused people to get colds.
2. 1️⃣ The number of online transactions increased rapidly. 2️⃣ The number of cyber fraud cases also rose. Choose the correct relationship.
easy
A. 1 → Cause; 2 → Effect
B. Both are effects of a common cause
C. 2 → Cause; 1 → Effect
D. Both are independent

Solution

  1. Step 1: Examine link

    Increased online transactions and more cyber frauds are related but both can stem from one factor - greater internet penetration.

  2. Step 2: Find the common cause

    Rise in digital use or availability of e-payment systems caused both trends.

  3. Final Answer:

    Both are effects of a common cause → Option B

  4. Quick Check:

    If internet use hadn’t grown, neither would have risen ✅
Hint: When both statements show a growth pattern, check for a shared external driver.
Common Mistakes: Confusing one as the cause of the other instead of recognizing a shared reason.
3. 1️⃣ Farmers are demanding higher minimum support prices (MSP). 2️⃣ Food inflation in the market has increased. Identify the correct cause-effect pattern.
easy
A. Both are independent
B. 1 → Cause; 2 → Effect
C. Both are effects of a common cause
D. 2 → Cause; 1 → Effect

Solution

  1. Step 1: Analyze connection

    Higher input costs (like fertilizers and fuel) may lead to both increased MSP demands and higher food prices.

  2. Step 2: Hidden reason

    Rising production cost is the common cause behind both events.

  3. Final Answer:

    Both are effects of a common cause → Option C

  4. Quick Check:

    If input costs fall, both demands and inflation will decline ✅
Hint: Economic cost hikes often trigger multiple related outcomes.
Common Mistakes: Assuming farmer demands directly caused inflation.
4. 1️⃣ There is a shortage of water in major cities. 2️⃣ Electricity production from hydropower plants has decreased. Choose the correct cause-effect identification.
medium
A. Both are effects of a common cause
B. 1 → Cause; 2 → Effect
C. 2 → Cause; 1 → Effect
D. Both are independent

Solution

  1. Step 1: Connect logically

    Water shortage and less hydropower can both result from poor rainfall.

  2. Step 2: Identify hidden cause

    Deficient monsoon is the shared reason for both effects.

  3. Final Answer:

    Both are effects of a common cause → Option A

  4. Quick Check:

    Normal rainfall → no shortage or fall in hydropower ✅
Hint: When environmental events affect multiple areas, look for one natural factor behind them.
Common Mistakes: Treating water shortage as the cause of low power generation.
5. 1️⃣ The number of mobile phone users increased drastically. 2️⃣ The number of internet service providers grew. Identify the correct relationship between the statements.
medium
A. 1 → Cause; 2 → Effect
B. 2 → Cause; 1 → Effect
C. Both are effects of a common cause
D. Both are independent

Solution

  1. Step 1: Analyze dependency

    Both trends could be due to the same factor - advancement in telecommunications and cheaper technology.

  2. Step 2: Confirm common origin

    Cheaper data and smartphones led to both rising usage and more service providers.

  3. Final Answer:

    Both are effects of a common cause → Option C

  4. Quick Check:

    If data costs were high, neither rise would occur ✅
Hint: When both trends show parallel growth, check for an external enabling factor.
Common Mistakes: Assuming more users directly caused increase in service providers (mutual effect, not direct cause).

Mock Test

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