Chapter 4: Designing Studies

sample

a part of the population where we are actually able to collect information. The data from this _______ helps us draw conclusions about the population as a whole

population

an entire group of individuals that we’re collecting information from

sample survey

a study that uses an organized plan to choose a sample that represents some specific population

voluntary response sample

consists of people who choose themselves by responding to a general appeal. Shows bias because people with strong opinions are most likely to respond.

design

an information gathering experiment in which a variation is present or not, and it shoul dbe performed under the full control of a researcher.

convenience sampling

takes data from those who are easiest to reach

biased

systematically favoring a certain outcome

simple random sample

where individuals from a population are chosen in a way that every set of n individuals has an equal chance to be in the selected sample.

table of random digits

a long string of digits 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, with these properties:

• each entry in the table is equally likely to be any of the 10 digits 0 through 9

• the entries are independent of each other. That is, knowledge of one part of the table gives no info about any other part.

probability sample

selection of a sample from a population when this selection is based on the principle of randomization.

stratified random sample

classifying the population into groups of similar individuals (strata). Afterwards, you can choose a separate SRS in each stratum and then combine these SRSs to form the full sample.

cluster sampling

a method that selects groups of individuals that are “near” one another. The groups chosen often mirror the characteristics of the population.

inference

when we use a process to draw a conclusion about a population on the basis of the sample data.

margin of error

comes with random samples that sets bounds on the size of the likely error.

strata

the groups formed in stratified random sampling.

undercoverage

occurs when some groups in the population are left out of the process of choosing the sample.

nonresponse

occurs when an individual chosen for the sample can’t be contacted or refuses to participate.

response bias

refers to various factors that may lead people to respond falsely or inaccurately to a question

sampling frame

the list from which the sample is actually chosen

systematic random sample

a probability sampling method in which researchers assign a desired sample size of the population and assign a regular interval number to decide who in the target population will be sampled.

observational study

gathers data on individuals as they are

experimental

where they actively do something to people, animals, or objects in order to measure their response.

confounding

when variables’ effects on a response can’t be distinguished from each other

lurking variable

a variable that’s not among the explanatory or response variables in a study but may influence the response variable.

experimental units

the smallest collection of individuals to which treatments are applied

subjects

when the experimental unit are humans

random assignment

uses chance to assign subjects to treatments. IT also created treatment groups that are similar before the treatments are applied.

treatment

specific conditions applied to the individuals in an experiment. If there are multiple explanatory variables, a treatment is a combination of the specific value of these variables.

factor

a combination of values of the explanatory variables.

level

used to describe the levels of measurement of a variable, a measure, or a scale to distinguish between measured variables that have different properties.

placebo effect

some patients get better because they expect the treatment to work even though they received an inactive treatment.

single blind experiment

where only the subject is unaware if htey’ve been given the explanatory variable.

control group

a group not receiving the new treatment being studied.

completely randomized experiment

a type of experimental design where the experimental units are randomly assigned to the different treatments

randomized block design

where are the experimental units are in groups called blocks. THe treatments are randomly allocated to the experimental units inside each block. When all treatments appear at least once in each block, here’s a completely ________________________.

matched pair design

where each subject receives both treatments in a random order, subjects are matched in pairs as closely as possible, and each subject in a pair receives one of the treatments.

statistically significant

measures the probability of the null hypothesis being true

replication

repetition of an experiment or observation in the same or similar conditions.

hidden bias

preferences for or against a person, thing, or groupheld at an unconscious level.

double blind experiment

where both the subject and the experimenter are unaware of who was given the explanatory variable.

block design

the arrangement of experimental units or subjects into groups called blocks.

data ethics

the principles behind how organizations gather, prtect, and use data.