1. Exploratory Data Analysis
1.4. EDA Case Studies
1.4.2. Case Studies
1.4.2.10. Ceramic Strength

Analysis of the Lab Effect

Box Plot The next matter is to determine if there is a lab effect. The first step is to generate a box plot for the ceramic strength based on the lab.

This box plot shows the following.

1. There is minor variation in the medians for the 8 labs.

2. The scales are relatively constant for the labs.

3. Two of the labs (3 and 5) have outliers on the low side.
Box Plot for Batch 1 Given that the previous section showed a distinct batch effect, the next step is to generate the box plots for the two batches separately.

This box plot shows the following.

1. Each of the labs has a median in the 650 to 700 range.

2. The variability is relatively constant across the labs.

3. Each of the labs has at least one outlier on the low side.
Box Plot for Batch 2

This box plot shows the following.

1. The medians are in the range 550 to 600.

2. There is a bit more variability, across the labs, for batch2 compared to batch 1.

3. Six of the eight labs show outliers on the high side. Three of the labs show outliers on the low side.
Conclusions We can draw the following conclusions about a possible lab effect from the above box plots.
1. The batch effect (of approximately 75 to 100 units) on location dominates any lab effects.

2. It is reasonable to treat the labs as homogeneous.