STATS 201->MIDTERM #1

Sample

a subset of the population of interest that we will collect data on

Experiments

a technique that tests predicted relationships among variables in a controlled environment

Lurking Variable

a variable that is not among the explanatory or response variables in a study but that may influence the response variable

Explanatory Variable

a variable that we think explains or causes changes in the response variable

Population

all individuals, objects, or things whose properties are being studied

Outlier

an observation of data that does not fit the rest of the data; some are due to mistakes while others may indicate that something unusual is happening

Placebo Effect

experimental results caused by expectations alone; any effect on behavior caused by the administration of an inert substance or condition, which the recipient assumes is an active agent.

frequency polygon (line graph)

raw scores on X-Axis, frequency on Y-Axis

Bin

represents a range of data that is used when displaying large data sets (AKA classes or intervals) All bins have the same width

Which samples are biased?

self-selection, under-representation

Time Plots

plot each observation against the time at which it was measured

Systematic Sampling

randomly select a starting point and take every nth data piece

Histogram

A graph of vertical bars representing the frequency distribution of a set of data. Class Def: Consists of contiguous (adjoining) bars. The horizontal axis is labeled with what the data represents. The vertical axis is labeled either frequency or relative frequency (or percent frequency or probability) of each bin. The graph will have the same shape with either label.

Stem Plot

A graphical display of quantitative data that involves splitting the individual values into two components

Response Variable

A variable that measures an outcome of a study.

Statistics

Collection of methods for planning experiments, obtaining data, organizing, summarizing, presenting, analyzing, interpreting, and drawing conclusions based on data.

Box Plots

Make sure the numbers are in order from least to greatest. Find the median, the Q1 and Q3 by finding the median again of the upper and lower sections.

Observational Studies

Researchers carefully and systematically observe and record behavior without interfering with behavior.

Interquartile Range (IQR)

The range of the middle fifty percent of the data values; the IQR is found by subtracting the first quartile from the third quartile.

Mode

The value that occurs most frequently in a given data set.

Parameter

a # that is used to represent a characteristic of the population and that generally cannot be determined easily

Standard Deviation

a computed measure of how much scores vary around the mean score

Confounding Variable

a factor other than the independent variable that might produce an effect in an experiment

Mean

average

What are possible problems involved in sampling?

confounding, misleading data

Cluster Sampling

divide population into clusters then randomly select some of the clusters; all members of these clusters are in the cluster sample

Numerical Variables

either discrete ( ) or continuous ( )

Categorical Variables

either nominal ( ) or ordinal ( )

Simple Random Sample (SRS)

every member of the population has an equal chance of being chosen

Descriptive Statistics

organizing and summarizing data

inferential statistics

formal methods for drawing conclusions

Data

the actual values of the variable; could be #s or words; datum is a single value

Range

the difference between the highest and lowest scores in a distribution

Median

the middle score in a distribution; half the scores are above it and half are below it

Convenience Sample

type of sampling that is non-random and involves using results that are readily available

Stratified sampling

we divide the population into groups (strata) and take an SRS from each