The Effective base = the squared sum of weights divided by the sum of squared weights

### Formula for Two independent sample Z test – Proportions

This is the formula used for calculating the “Two independent sample Z test” for proportions. The yellow highlighted base sizes use the effective base instead of the weighted base size when the option is applied.

### Formula for Two independent sample Z test – Means

This is the formula used for calculating the “Two independent sample Z test” for mean values. The yellow highlighted base sizes use the effective base instead of the weighted base size when the option is applied.