## Step 1

#### Step

Subtract the alpha value from 1. The alpha value is expressed as decimal less than one. As an example, say the alpha value is .03:

1 - 0.03 =0.97

## Step 2

#### Step

Divide the result from above by 2. All two-tailed tests must have this step. The result is 0.97/2 or 0.485

## Step 3

#### Step

Look up the result on a Z-table. If the number itself is not present, then choose the closest match. In the case of the example, 0.485 happens to be displayed on a Z-table.

## Step 4

#### Step

Find the corresponding number of the row in the far left column, which in this case is 2.1.

## Step 5

#### Step

Find the corresponding number of the column at the top row, which in this case is 0.07

## Step 6

#### Step

The critical value is the sum of 2.1 + .07 or 2.17.