Sampling & Experimental Design Review AP Stats

2. KNOW YOUR SAMPLING METHODS
• CENSUS – NOT SAMPLING BUT IS THE ANTI-SAMPLING METHOD, INCLUDES ENTIRE POPULATION – DIFFICULT
• CONVENIENCE SAMPLING (NOT GOOD METHOD) – NOT RANDOM
• CLUSTER SAMPLING – RANDOMLY SELECT HETEROGENEOUS GROUPS, ENTIRE CLUSTER SURVEYED
• MULTISTAGE SAMPLING – COMBINATION OF METHODS
• SIMPLE RANDOM SAMPLING (SRS) – RANDOM SELECTION FROM ENTIRE POPULATION
• STRATIFIED RANDOM SAMPLING – HOMOGENEOUS GROUPS – SRS FROM EACH GROUP
• SYSTEMATIC RANDOM SAMPLING –EVERY NTH PERSON FROM ENTIRE POPULATION

3. KNOW BIAS
• CONVENIENCE SAMPLING– NOT RANDOM
• LEADING (WORDING OF) QUESTIONS – WORDING OF QUESTIONS LEADS TO A CERTAIN RESPONSE
• NONRESPONSE - MANY MEMBERS OF THE SAMPLE DO NOT RESPOND, THEREFORE RESULT MAY DIFFER
SIGNIFICANTLY FROM RESULT IF ALL HAD RESPONDED
• UNDERCOVERAGE – SOME MEMBERS OF THE POPULATION ARE EXCLUDED
• VOLUNTARY RESPONSE – THOSE WITH STRONGEST OPINIONS RESPOND

4. KNOW EXPERIMENTAL DESIGNS
• BLOCK DESIGN – SEPARATE EXPERIMENTAL UNITS IN GROUPS (BLOCKS) THAT ARE SIMILAR TO EACH
OTHER. THE BLOCKING FACTOR IS SOMETHING THAT IS NOT OF PRIMARY INTEREST TO THE RESEARCHER.
• MATCHED PAIRS DESIGN – SEPARATE EXPERIMENTAL UNITS IN PAIRS THAT ARE SIMILAR TO EACH OTHER
(OR THE SAME PERSON), THE TREATMENT IS RANDOMIZED BETWEEN EACH PAIR
• DOUBLE BLIND – NEITHER THE RESEARCHER NOR THE SUBJECT KNOWS WHICH TREATMENT THE SUBJECT
RECEIVES
• SINGLE BLIND – THE SUBJECT DOES NOT KNOW WHICH TREATMENT HE/SHE RECEIVES

5. KNOW PRINCIPLES OF EXPERIMENTAL DESIGN
• CONTROL - MAKE THE EXPERIMENT MORE EFFICIENT BY CONTROLLING FOR LURKING/CONFOUNDING
VARIABLES, REDUCES EXPERIMENTAL ERROR
• RANDOM ASSIGNMENT – REDUCES BIAS, ENSURES THAT RESULTS ARE STATISTICALLY VALID
NOTE: KNOW DESCRIPTIONS OF PROPER USE OF RANDOM DIGITS TABLE AND OTHER
RANDOMIZATION METHODS
• REPLICATION – MULTIPLE EXPERIMENTAL UNITS RECEIVE EACH TREATMENT, PROVIDES ESTIMATE OF
EXPERIMENTAL ERROR

6. KNOW YOUR VOCABULARY
• CONTROL GROUP
• EXPLANATORY VS RESPONSE VARIABLE
• BIAS
• CONFOUNDING AND LURKING VARIABLES
• PLACEBO EFFECT
• SIMULATION
• TERMS ALREADY USED IN THIS REVIEW 

7. ALWAYS GOOD TO KNOW
• CORRELATION DOES NOT EQUAL CAUSATION! REMEMBER THAT JUST BECAUSE YOU OBSERVE A
RELATIONSHIP, IT TAKES MORE TO ESTABLISH A CAUSE-AND-EFFECT RELATIONSHIP. EXPERIMENTS CAN
SHOW DIRECT CAUSE-AND-EFFECT RELATIONSHIPS, WHEREAS AN OBSERVATIONAL STUDY CANNOT.
• AP STATS REQUIRES CRITICAL THINKING SKILLS TO BE TURNED ON AND UP! READ EACH AND EVERY
CHOICE CAREFULLY AND THINK! THINK! THINK! THE WRONG ANSWER MAY SOUND RIGHT UNTIL YOU
READ THE CORRECT CHOICE!!