Prof Randi Garcia
April 16, 2018
In an experiment, researchers wanted to compare how easy it is to remember four different kinds of words: 1) concrete, frequent: fork, brother, radio,… 2) concrete, infrequent: blimp, warthog, fedora, … 3) abstract, frequent: truth, anger, foolishness, … and 4) abstract, infrequent: slot, vastness, apostasy, …
Ten students in a psychology lab served as subject. During each of the 4 time slots, subjects heard a list of words from one of the four kinds, and then was tested for recall.
There are two possible models for chance error in models with compound within-block factors.
How can we decide?
\[ F = \frac{{MS}_{Factor}}{{MS}_{Error}} \]
\[ F = \frac{{MS}_{Factor}}{{MS}_{Blocks\times Factor}} \]
\[ F = \frac{{MS}_{Factor}}{{MS}_{Blocks}} \]
Each of eight patients, while in surgery, had oxygen pressure readings taken in two of their veins, hepatic and portal, under two conditions, control and with the femoral artery clamped. Units of measurement of the response variable are mm HG (millimeters of mercury).
Worms that live at the mouth of a river must deal with varying concentrations of salt. Osomoregulating worms are able to maintain relatively constant concentration of salt in the body. An experiment wanted to test the effects of mixtures of salt water on two species of worms: Nereis virens (N) and Goldfingia gouldii (G). Eighteen worms of each species were weighted, then randomly assigned in equal numbers to one of three conditions. Six worms of each kind were placed in 100% sea water, 67% sea water, or 33% sea water. The worms were then weighted after 30, 60, and 90 minutes, then placed in 100% sea water and weighted one last time 30 minutes later. The response was body weight as percentage of initial body weight.
For the walking babies example (pg. 150) below are (rounded) average times to walk (months) for the four groups. Compute the estimates for the following set of three comparisons: i) Exercise vs. no exercise, ii) Special exercise vs. exercise control, and iii) Weekly report vs. final report.
Draw a diagram with arrows depicting the top-down approach taken with this set of comparisons.
\[ comparison \pm t^* \times SE \]
\[ SE = \sqrt{{MS}_{Error}}\times\sqrt{\frac{1}{{n}_{1}}+\frac{1}{{n}_{2}}} \]
When we do multiple significance tests, our effective type I error rate is inflated. Most statisticians agree that we should adjust our type I error rate to account for our multiple tests, and control the expriment-wise error rate.
There are four methods discussed in the chapter:
For comparisons in designs with compound within block factors.
Constant Within-blocks Interactions with the Comparison Factor (CWIC) Rule: