BIO 4118 APPLIED BIOSTATISTICS ASSIGNMENT 1 GRADING SCHEME
My solutions to this assignment can be found in the accompanying solutions
document (Assignment 1 solutions). Please note that there are some things in my
solutions (e.g. Cochran’s test of a linear trend) which go somewhat things that were
directly addressed in the labs and/or lectures.
I.
Examination of the data
I.1. Some evidence that you had examined the risk trend with age (e.g. a plot,
table, statement of trend etc)
I.2. Some indication that you have interpreted this trend
II.
Preliminary contingency table analysis
II.1. Contingency analysis using all 7 age classes, and appropriate interpretation
II.2. Evidence that you understood the directionality of the biological hypothesis
versus the non-directionality of this analysis.
II.3. Evidence that you understood the next step, i.e. multiple comparisons among
adjacent age classes
III.
Detailed contingency table analysis
III.1. Testing for homogeneity of subgroups, beginning with two youngest age
classes
III.2. Understanding that 2 X 2 tests require corrections, even though in this case
it doesn’t matter.
III.3. Conclusion that that combining age classes is only statistically justified for
first two classes
IV.
Log-linear model analysis
IV.1. Fitting of log-linear model using all age classes
IV.2. Comparison of goodness of fit of models with no age classes combined (the
most complex model) and models where first 2, 3 age classes have been
combined, and appropriate conclusions
V.
The biological hypothesis reconsidered
V.1. Evidence of understanding that null under original MCA could be rejected,
but biological hypothesis still not be corroborated.
V.2. Evaluation of biological hypothesis by examination of patterns in raw data.
VI.
One step further…
VI.1. Statistical tests for linear increase in risk with age (Cochran’s linear trend,
regression on transformed values, etc.)
IV.2. Interpretation of lambdas from fitted log-linear model
IV.3. Examination of residuals from final “best” model (This is not really one
step further, but so few people did it that I concluded that I underemphasized it in
the labs/lectures!)
IV.4. Biological versus statistical significance of results (is the statistically
significant increase in risk between 2-25 and 25-29 biologically significant),
especially with respect to the power issue.
On the front of your paper, you will find a summary table of the extent to which,
in my view, these issues were addressed in your solution, and the corresponding grade
(out of 5). If you feel I have been unduly harsh (or generous), see me and we will chat
about it.