AP Statistics Chapter 5 Section 2

Surveys Consider these things: Bias poor wording confusion on your part as how to answer the question, overall appearance (spelling, grammar, etc.) Can you tell the purpose of the survey? Have you been given directions about answering the questions? Is it clear how the data will be used? Anonymous? Confidential?

Vocab Observational Study Experiment Experimental units, subjects Treatment Factors Placebo effect Control group Three Principles of Statistical Design Statistically significant Hidden bias Double blind experiment Lack of realism Block design Matched pairs design

Instant Breakfast A food company assesses the nutritional quality of a new “instant breakfast” product by feeding it to male rats. The response variable is the rat’s weight gain over a 28-day period. A control group of rats eats a standard diet but otherwise receives exactly the same treatment as the experimental group. The experiment has one factor – the diet of the rats.

Instant Breakfast

SRS OF RATS Label: 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Math Prb Rand(01,30,15) sto L1 Rats: 3, 4, 5, 7, 10, 11, 12, 16, 18, 20, 21, 22, 23, 29, 30 18 was repeated so repeat the random process for one more number. (20 was the next number) The rats with these labels will make up the treatment group the remaining rats will be in the control group.

Three Principles of Statistical Design Control of the lurking variables. Randomization – the use of chance to select all parts of the study Replication – repetition of each treatment on a large enough number of subjects to allow the systematic effects of the treatment to be seen.

Randomized comparative design Randomization produces groups of experimental units that should be similar in all respects before the treatments are applied. Comparative design ensures that influences other than the experimental treatments operate equally on all groups. Therefore, differences in the response variable must be due to the effects of the treatments.

Statistically Significant IMPORTANT TO KNOW: Is the observed effect too large to attribute plausibly to chance? Could this just be coincidence? Larger groups are better at showing the effects Equal size comparative groups are better

Blind or Double Blind Blind – the subject does not know which treatment he/she is a part of: treatment or control. Double Blind – the subject nor the data collector know which treatment a particular subject is a part of: treatment or control. This provides control of bias that could be brought into play by the placebo effect or the desire of the data collector for a particular outcome.

Block Design to compare the effectiveness of three TV advertisements The belief is that men and women react differently to TV advertisements therefore blocking by gender is done in the design.

Show the randomization for the placement of 24 women and 12 men to specific treatments. Factor B Repetitions 1 3 5 Factor A 30 sec 2 Length 90 sec 4 6 23, 9, 1, 24, 7, & 3 are repeats – push enter to get the next random numbers – keep them in order 11 will replace 23 12 will replace 3 8 will replace 9 19 will replace 23 15 will replace 1 17 will replace 24 16 will replace 7

8 will be replaced with 11 10 will be replaced with 9 10 will be replaced with 2 6 will be replaced with 1 12 will be replaced with 7

Women: 01, 02, 03, 04, 05, 06, 07, 08, 09, 10, 11, 12, 13, 14, 15 16, 17, 18, 19, 20, 21, 22, 23, 24 Men: 01, 02, 03, 04, 05, 06, 07, 08, 09, 10, 11, 12 Treatment 1: 1 repetition, 30 sec: (Women)- 23, 22, 4, 13 (Men) – 4, 10 Treatment 2: 3 repetitions, 30 sec: (Women) – 10, 18, 2, 9 (Men) – 12, 6 Treatment 3: 5 repetitions, 30 sec: (Women) – 24, 5, 20 , 11 (Men) – 5, 3 Treatment 4: 1 repetition, 90 sec: (Women) – 6, 8, 1, 19 (Men) – 8, 11 Treatment 5: 3 repetitions, 90 sec: (Women) – 3, 15, 14, 21 (Men) – 9, 2 Treatment 6: 5 repetitions, 90 sec: (Women) – 17, 7, 16, 12 (Men) – 1, 7

Block or Strata? Blocking or creating a stratified sample appear to be doing the exact same thing. They are – both group similar units. Blocking is the term when you are talking about the design of an experiment. Stratified is the term is you are talking about sampling.

Matched Pairs Design A common form of blocking for comparing just two treatments. Can be a pre- and post-test situation Can be a taste test situation