Statistics Section 1.3 Describe the components and types of censuses Review: Distinguish between a population and a sample and relate them the inferential and descriptive statistics. Distinguish between the four levels of measurements. Describe the techniques of simple random, stratified, random, systematic, cluster, multistage, and convenience sampling. Procedure for planning a statistical study 1. Identify the objects of interest 2. Specify the variables, and method of making measurements 3. Determine whether to use entire population or a sample 4. Collect the data 5. Analyze and report results In a census, measurements or observations are made from the entire population. In a sample, measurements or observations are made from part of the population.

Types of statistical studies Observational study – observations and measurements are made of individuals in a way that does not change the response or variable being measured. Experiment – a treatment is imposed on the individuals in order to observe a possible change to the response or variable being measured. Identify the type of statistical study. The population of wild honey bees is declining. Observations of bees are make throughout fields where conventional agricultural practices are followed. Observations of bees are made throughout fields where all uses of pesticides and herbicides are prohibited.

Experimental studies require a control to determine the effectiveness of a treatment. A control makes a comparison between individuals that receive no treatment and those that do receive treatment. Types of controls No treatment Placebo – the subject receives no treatment but mistakenly thinks that he or she is. Placebo Effect – a subject responds favorable when they think that they are receiving treatment but in reality are not.

A completely randomized experiment is one in which a random process is used to assign each individual to one of the treatments. Patients with chest pains undergo treatment to relieve pain

A randomized block experiment is one in which individuals are first sorted into blocks and then a random process is used to assign each individual to one of the treatments. Patients with chest pains undergo treatment to relieve pain

Features of good experimental design Control group- receives a placebo. It is used to account for the influence of unknown variables sometimes called lurking or confounding variables. Randomization – prevents bias in selecting members for each group. Replication – reduces the chance that differences in the two groups occurred by chance. Many experiments are double blind experiments, which means neither the individuals in the study nor the observers know which subjects are receiving treatment.

A survey is used to gather data by asking individuals questions. Guided exercises page 25 A survey is used to gather data by asking individuals questions. Potential problems with surveys (page 26) Non response Truthfulness of responses Faulty recall Hidden bias Vague wording Interviewer influence Voluntary response Guided exercises page 27

Assignment Page 29 Problems 2,4,5,6,7,8,10 Read page 28 – 29 choosing data collection techniques and the placebo effect Assignment Page 29 Problems 2,4,5,6,7,8,10