# Cohort and Retention Analysis (Data Analytics)

> Time-based cohorts, cohort retention, RFM analysis, customer segmentation, churn prediction

- 20 interview questions
- Mid-Level
- [Interview Questions: Data Analytics](https://sharpskill.dev/en/technologies/data-analytics/interview-questions.md)

## 1. What is a cohort in data analysis?

**Answer**

A cohort is a group of users who share a common characteristic over a given period, most commonly the date of their first action (signup, first purchase). Grouping users into cohorts allows comparing their behavior over time and identifying trends across acquisition periods. It is a fundamental tool for measuring retention and evaluating the impact of product changes.

## 2. What is the most common criterion for defining a time-based cohort?

**Answer**

The most common criterion for defining a time-based cohort is the date of first signup or first purchase. Grouping by acquisition period (week, month, quarter) enables objective comparison of user behavior across different acquisition moments. This helps isolate the effect of time and detect improvements or degradations linked to product or marketing changes.

## 3. How to read a cohort retention table?

**Answer**

A cohort retention table is read with cohorts as rows (by acquisition period) and subsequent periods as columns (Month 0, Month 1, etc.). Each cell shows the percentage of users from that cohort still active at that period. The first column is always 100%, and values naturally decrease over time. This format allows visual comparison of retention across cohorts.

## 17 more questions available

- What is the difference between Day-N retention and rolling retention?
- Why is retention considered a more reliable metric than the number of active users?

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