Section 1

Statistics

the art of collecting, organizing, summarizing, and describing data as well as drawing inferences from the data.

extraneous factor

anything that can affect the outcome, other than the treatment or condition being studied

descriptive statistics

collecting data, organizing data, summarizing data, and describing data

Inferential Statistics

drawing conclusions from the data

population

the complete set of units we are interested in studying

sample

a subset of the population

Well representative sample

a sample in which the characteristics of the sample match the characteristics of the population

Parameter

a numerical value based on the population

statistic

a numerical value based on the sample

variable

a characteristic that takes on different values for different people, places, or things is labeled a variable

constant

values in the population that do not vary are known constants

Is a parameter a variable or constant?

constant

Is a statistic a variable or a constant?

variable

Probability

measures how likely it is for something to occur

Random Variable

a variable is a random variable if the exact value of the variable cannot be predicted in advance.

Quantitative random variable

a variable that can be measured in the usual sense

Qualitative Random Sample

a characteristic that cannot be measured in the usual sense; it can only be out into categories

Discrete Random Variable

when the variable can only assume specific values

continuous random variable

when the variable can theoretically assume any value on a given interval

Measurement

the assignment of numbers to objects or events according to a set of rules

the nominal scale

“naming observations” or classifying them into various mutually exclusive categories

the ordinal scale

when the measurements can be ranked according to some criterion

the interval scale

when the measurements cannot only be ranked, but the distance between any two measurements is known.

the ratio scale

measurements in which equality of ratios as well as equality of intervals is known.

census

when all subjects/objects of the population are sampled

nonprobability samples

the laws of probability are NOT used to obtain the samples

sample of convenience

the samples already exist

Haphazard Selection

the researcher and the subjects causually meet

Judgment Sampling

the researcher uses his/her own judgement in choosing the subjects

expert sampling

an “expert” picks the subjects

quota sampling

subjects are chosen so as to satisfy certain quotas that match the population

probability samples

the sample is obtained by a chance process

simple random samples

all samples of the same size have equal probability of being selected

stratified random sample

population is divided into subpopulations (strata) and a random sample is obtained from each strata

cluster samples

population is once again divided into stratas or clusters

systematic sampling

choose a random starting point from a list of subjects and then select nth subject on the list

sampling error

the extent to which the value of a statistic may differ from the parameter is predicts because of the way results vary from sample to sample

Selection bias

occurs when one excludes a specific characteristic or segment of the population

response bias

occurs when subjects respond incorrectly by lying or exagerating or forgeting or not understanding the question

nonresponse bias

occurs when the response rate is low

observational study

when the researcher simply observes the subjects in a specific situation or “natural habitat”

prospective studies

a study in which subjects are followed over a specified period of time and info is collected as it happens and into the future.

A prospective cohort study

when two groups, the cases are followed over a period of time to see if the cases develop the disease

Retrospective studies

a study in which data is obtained by looking back in time

a retrospective case-control study

is study in which past data is gathered from the group of controls and the cases to determine differences

designed experiment

has thee basic principles: control, randomization, and replication

treatment group

the group that receives the treatment

control group

group that does not receive the treatment

confounding factor

anything that affects the outcome of the experiment other than the treatment

blind study

when the subjects don’t know if they are receiving the treatment or a placebo

double blind study

when neither the subjects nor the doctors know if subjects are in the treatment or control group.

placebo effect

when subjects improve because they believe they are receiving the treatment

rosenthall effect

when the researcher or experimenter unintentionally influences the outcome through facial expressions, body language, or voice

hawthorne effect

when the outcome is affected because people change how they behave because they know they are being watched