Sitka89 data frame has 632 rows and 4 columns. It gives repeated
measurements on the log-size of 79 Sitka spruce trees, 54 of which
were grown in ozone-enriched chambers and 25 were controls. The size
was measured eight times in 1989, at roughly monthly intervals.
This data frame contains the following columns:
- measured size (height times diameter squared) of tree, on log scale.
- time of measurement in days since 1 January 1988.
- number of tree.
"ozone"for an ozone-enriched chamber or