# PSYC 1010 Study Guide - Midterm Guide: Square Root, Systematic Sampling, Normal Distribution

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Published on 18 Apr 2013

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Psych 1010 midterm 1 study notes

Chapter 1

- Branches of statistics

o Descriptive

Organize summarize and communicate numerical information

o Inferential statistics

Using data collected from a sample to draw conclusions about

a population

- Population: set of all observations in a particular study

- Sample: A set of observations drawn from a population of interest for

inclusion in a study

- Parameter: value that described population

- Statistic: value that describes sample

- Variables

o Discrete variables

Can only take on specific values (integers)

Measures how many

o Continuous variables

Full range of values

Measures how much

o Always discrete:

Nominal variables

Observations with names or categories as values

Qualitative not quantitative differences between

categories

Ordinal variables

Ranked by size or magnitude

Know rank but no info about size intervals

o Scale variables

Sometimes discrete, sometimes continuous

Interval

Observations of ordered numerical values with

intervals of equal size, no meaningful zero

Ratio

Observations of ordered numerical values with

intervals of equal size, but there is a meaningful zero

Can form ratios

- Operational definition

o Set of procedures used to measure or manipulate a variable

- Confounding variable

o Uncontrolled variable that it unintentionally allowed to vary

systematically with the independent variable

- Reliability

o Consistency of measure

- Validity

o Extent that the test measures what it is supposed to measure

- Research designs

o Correlational method

Association between two or more variables

No manipulation, only observation

o Experimental method

Randomly assign participants to levels (groups) of the

independent variable

Able to make causal conclusions (effect of IV on DV)

- Control confounding variables

o Random assignment to groups

Chapter 2

- Frequency distributions: gives number of times each possible value of a

variable occurs in a data set

o Frequency table

o Grouped frequency table

Used for large range of scores and data to several decimal

places

Full range = Xmax – Xmin +1

Use 10 intervals

No gaps

o Frequency histograms

Represent scale data (interval and ratio)

Can have polygon overlay (lines over bars)

o Frequency polygon

Also represent scale data (looks more like line graph)

o Grouped histogram

Use middle of interval at bottom (e.g 7.5 not 0-14.99)

o Grouped polygon

Same as histogram, use middle point

- Histograms vs. bar graphs

o Histograms are used for interval or ratio scales of measurement, bars

touch

o Bar graph bars do not touch, used for nominal or ordinal data

- Normal distribution

o Bell-shaped

o Symmetrical around the mean

o Unimodal (only one peak)

- Skewed distributions

o Positive skew

tail more to the right

May reflect floor effect (you can’t score any lower)

## Document Summary

Organize summarize and communicate numerical information: inferential statistics. Using data collected from a sample to draw conclusions about a population. Population: set of all observations in a particular study. Sample: a set of observations drawn from a population of interest for inclusion in a study. Can only take on specific values (integers) Observations with names or categories as values. Know rank but no info about size intervals: scale variables. Observations of ordered numerical values with intervals of equal size, no meaningful zero. Observations of ordered numerical values with intervals of equal size, but there is a meaningful zero. Can form ratios: set of procedures used to measure or manipulate a variable. Confounding variable: uncontrolled variable that it unintentionally allowed to vary systematically with the independent variable. Validity: extent that the test measures what it is supposed to measure. No manipulation, only observation: experimental method. Randomly assign participants to levels (groups) of the independent variable.