What are the AP Readers Looking For?

Sessions III & IV

Describing a Distribution

Discuss center, shape, and spread in context.

Center: Mean or Median

Shape: Roughly Symmetrical, Right or Left Skewed

Spread: Standard Deviation, IQR, Range, or Spread

Linear Regression

Don’t forget about formulas on chart. r is the correlation coefficient. r^2 is the coefficient of determination. r has no units Strong r indicates association, not causation. r is not affected if x & y are reversed or if

operations (mult, divide, add, sub) are performed on each x or on each y.

ˆ, is always on x y y a bx

Linear Regression

r^2 describes the percent variation of the response variable, y, explained by the linear relationship (LSRL) with the explanatory variable, x. PUT IN CONTEXT!

When discussing r, describe line as weak, moderate, or strong linear relationship between x & y (in context).

Interpret slope by saying…For every one unit increase in the explanatory variable, the response variable increases/decreases by about “b” units.

Experimental Design

Randomization – what to say Blocking – always say why Avoid use of terms confounding & bias Bias is never eliminated only reduced Why do we randomize?

2007 MC Question # 35

A group of students has 60 houseflies in a large container and needs to assign 20 to each of three groups labeled A, B, and C for an experiment. They can capture the flies one at a time when the flies enter a side chamber in the container that is baited with food. Which of the following methods will be most likely to result in three comparable groups of 20 houseflies each? See handout

Experimental Design

Completely randomized design– Randomly sort to treatment groups – Identify treatment groups by name– State what is to be measured

Double Blind

Neither the participant nor the person who is evaluating the results is aware of who is getting the treatment.

Blocking

We block to create homogenous groups– Blocking reduces variation– When variation is reduced, the standard deviation of

the responses decreases.– We can more readily see the effects of the

treatment.

Probability Questions

Show as much work as possible to justify your answers

Link answers to work “Calculator speak” is ok, but not enough to

justify your answer. What do you do if you can’t figure out the

answer to a probability question and need it to respond to part b).

Scoring a Significance Test

1 pt for the null and alternative hypotheses & defining the parameter.

1 pt for assumptions & either the test statistic and formula OR name of the test

Scoring a Significance Test

1 pt Mechanics; the value of the test statistic & p-value

1 pt for decision referencing alpha & conclusion in context.