2. There are 2 Categorical Variables
1. Infants Aged 2 months & Infants Aged 6
months
Wait, why is that categorical, those are numbers? Why
isn’t that ordinal?
Because categorical variables SORT individuals into groups
Ordinal level variable are scalable and are ordered 1, 2, 3, 4—
the example in the power point might be confusing you
because: freshman = 1, sophomore = 2, etc  categories
have been assigned numbers that can be ORDERED
2. Control group (no mercury) versus not exposed

3. Interval Variables
• Body Weight
• Blood level of mercury
• Urinary level of mercury
• Stool level of mercury
ALL CAN be measured (not approximated).

5. So what about this p value thing?
• The probability that the finding is due to
chance….
• There are several findings (results) listed in
this article, which ones matter?
– You really do have to read the article once or
twice to fully appreciate
– First what was the aim of the study?

6. Finding 1
• The mean concentration of blood mercury in
samples with quantifiable mercury was higher
in 2-month-olds than in 6-month olds
(difference3·05 nmol/L, 95% CI 0·03–1·24,
p=0·06)
– The difference is clinically significant, but the p
value is slightly higher than statistical significance
– Blood levels went down over time

7. Finding 2
• The mean mercury concentration in the stools
of these infants (no thiomerisol) was 22 ng/g
dry weight (SD 16), which was significantly
lower (p=0·002) than the mean of the samples
collected from thiomersal-exposed infants.
• The infants were excreting mercury in their
stool