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statistics define

the science of collecting organizing and interpreting data

statistics is

the data that describes or summarizes something.

population

the complete set of people or things being studied

sample

a subsect of the population from which the raw data are obtained

Population parameteres

specific characteristics of the population that a statistical study is designed to estimate.

sample statistics

are number or observations that summarize the raw data.

representative sample

is a sample in which the relevant characteristics of the sample members match those of the population.

simple random sampling

we choose a sample of items in such a way that every sample of a given size has an equal chance of being selected

systematic sampling

we use a simple system to choose the sample, such as selecting every 10th or every 50th member of the population.

convenience sampling

we use a sample that is convenient to select, such as people who happen to be in the same classroom

stratified sampling

we use this method when we ar concerned about differences among subgroups, or strata, within a population. we first identify the subgroups and then draw a simple random sample with in each subgroup. the total sample consists of all the samples from the individual subgroups.

bias

if a study's design or conduct tends to favor certain results

observational study

researchers observe or measure characteristics of the sample members but do not attempt to influence or modify these characteristics

experiment

researchers apply a treatment to some or all of the sample members and then look to see whether the treatment has any effects.

treatment group

in an experiment is the group of sample members who receive the treatment being tested.

control group

is the group who do not receive the treatment being tested

placebo

lacks the active ingredient of a treatment being tested in a study, but is identical in appearance to the treatment.

placebo effect

refers to the sistuation in which patients imporve simply b/c they believe they are receiving a useful treatment.

single blind

if the participants do not know whether thay are members of the treatment group or members of the control group , but the experiments do know.

double blind

participants and experimenters do not know who belongs to the treatment group or control group.

margin of error

is used to describe a confidence interval that is likely to contain the tru population paramenter. We find this interval by subtracting and adding the margin of error from the sampl statistic obtained in the study. ie.from = sample stat - margin of error or to = sample stat + margin of error

selection bias

occurs whenever researchers select their sample in a way that tends to make it unrepresentative of the population.

participation bias

mostly happens with surveys and polls. when people choose to participate.

variable

any item or quantity that can vary or take on different values. In statistics it is the items you seek to measure.

Frequency table

2 columns where one is frequency and the other is categories.

qualitative data

describes qualities or categories

quantitative data

represent counts or measures.

histogram

is a bar graph for quantitative data catefories. the bars have natural order and the bar widths have specific meaning.

line chart

shows the data value for each category as a dot and the dots are connected with lines.

time-series diagram

is a histogram or line chart in which the horizontal axis represents time.

stack plots

shows different data sets in a vertical stack.

correlation

exists between two variables when higher values of one variable consistently go with higher values of another or when higher values of one variable consistently go wieht lower values of another.

scatter diagram

is a graph in which each point represents the values of two variables.

no correlation

there is no apparent relationship between the two variables.

positive correlation

both variables tend to increase or decrease together

negative correlation

2 variables tend to change in opposite direction.

strength of correlation

the more closely 2 variables follow the general trend the stronger the correlation.