## Population vs Sample

**Population**: every member of a group.**Sample**: a subset of member that time and resources allow you to measure.

The main 2 concepts often discussed for Measurements of Data

1.

Measures of Central Tendency

This is divided into 3 categories

a. **Mean: **Its the average of numbers. (add up all the numbers, then divide by how many numbers there are)

b. **Median**: Its the middle value of numbers. (for odd numbers its n+1/2 )

c. **Mode**: Its the most occuring value.

2. Measures of Dispersion

This is divided into 3 categories

a. **Range**: its the difference between maximum value and minimum value.(max-min)

b. **Variance**: It is calculated as sum of square distance from each point to the mean → S² = Σ(x-x̄)²/(n-1)

c. **Standard Deviation**: Its the square-root of Variance — S = √(Σ(x-x̄)²/(n-1))