Chapter 4: Collecting Data

label the population 1-n, use random number table or calculator to generate random numbers (ignoring repeats), select those individuals

grouping individuals into strata based on a homogenous characteristic, take an SRS from each strata

make heterogeneous groups, choose a few of these groups, every individual in selected group included

choose random starting point, choose every nth individual from there to sample

systematic tendency to favor certain responses over others; leads to inaccurate data

when part of the population has a reduced chance of being included in a sample

when individuals chosen for a sample do not respond- leads to bias if these individuals differ from respondents

when writing about bias

occurs when an invitation is sent to all individuals in a pop. to participate; those who choose to participate may differ from individuals who don’t

when survey questions are confusing or leading

when individuals inaccurately report their own traits

4 principles of experimental design

keep other variables constant

using 2 or more treatments, such as a placebo

using large number of experimental units

subjects are unaware of which treatment they are recieving

subjects and those administering treatment don’t know which treatment subjects are receiving

observing and recording, no variables changed

imposing a treatment, explanatory and response variables, control group

experimental units assigned to the treatments completely at random

individuals put into homogenous “blocks,” random assignment of experimental units is carried out separately within each block

two very similar experimental units are paired and the two treatments are randomly assigned within each pair

each experimental unit receives both treatments in a random order

how to randomly assign

random assignment can conclude…

random selection can conclude…

selects individuals from the pop. who are easy to reach, leads to biased and inaccurate data

2 variables are associated in such a way that their effects on a response variable cannot be distinguished from each other

specific condition applied to individuals in an experiment (combo of levels)

the object to which a treatment is randomly assigned

explanatory variable that is manipulated and may cause a change in the response variable

different values of a factor

data from a sample unlikely to be the exact same as data from entire population

choosing a starting point for systematic random sample