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PSYC STats CH.1 Population and sample, Summaries of Experimental Psychology

Rochester Institute of Technology (RIT)Experimental Psychology

PSYC STats CH.1 Population and sample

Typology: Summaries

2021/2022

Uploaded on 09/20/2023

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08. 30. 2023
Chapter 1: Introduction to Statistics
- Variables:
- Characteristic that can change or take on different values
- Most research begins with a general question about the relationship between 2
variables for a specific group
- Example: Do psychedelics improve symptoms in depressed adults?
- Population:
- An entire group of individuals is called population
- All PSYC 243 students in Fall 2023
- All voters in the United States
- Example research question:
- What's the relationship between weekend drinking (variable 1) and academic
performance (variable 2) among first-year college students (population) ?
- Sample:
- Usually populations are so large we cannot examine the entire group
- Therefore, a sample is selected to represent the population
- Goal is to use results from a sample to answer questions about the
population
- Populations and Samples:
- Inferential Statistics:
- What is an inference ?
- Inference statistics - use sample data to make general conclusions
(inferences) about populations
- Example: presidential polling
-
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Chapter 1: Introduction to Statistics

- Variables: - Characteristic that can change or take on different values - Most research begins with a general question about the relationship between 2 variables for a specific group - Example: Do psychedelics improve symptoms in depressed adults? - Population: - An entire group of individuals is called population - All PSYC 243 students in Fall 2023 - All voters in the United States - Example research question: - What's the relationship between weekend drinking (variable 1) and academic performance (variable 2) among first-year college students (population)? - Sample: - Usually populations are so large we cannot examine the entire group - Therefore, a sample is selected to represent the population - Goal is to use results from a sample to answer questions about the population **- Populations and Samples:

  • Inferential Statistics:** - What is an inference? - Inference statistics - use sample data to make general conclusions (inferences) about populations - Example: presidential polling -

- Applied Inferential Statistics WWII - Sample data provide limited information about the population - Therefore sample statistics are not perfect representatives of population parameters - Descriptive Statistics: - Methods for organizing and summarizing data: - Tables or graphs are used to organize data - Descriptive values used to summarize data - Descriptive value for a: - Population = parameter **- sample = statistic

  • Sampling error:**
    • The discrepancy between a sample statistic and its population parameter is called sampling error
    • Defining and measuring sampling error is a large part of inferential statistics

- Data: - Measurements obtained in research are called data - Goal of statistics is to help researchers organize and interpret data - Types of variables: - Discrete variables: ex: a dice roll, consists of indivisible categories - Continuous variables: time or weight, infinitely divisible into any unit the researcher chooses - Measuring variables: - To establish relationships between variables, we must measure the variables we are interested in - To do that we choose a scale of measurement - 4 major scales of measurement - The scale we choose determines the types of questions we can answer with our data

  • Examine the relationship between 2 or more variables by changing one variable and observing the effects on the other variable - The Black box of humanity demo

  • Independent variable (IV) - a condition or event manipulated by experimenter

    • I decide

  • Dependent variable (DV) - an aspect of behavior thought to be affected by the independent variable. DVs are measured, not manipulated - Depends on what I decide

  • Ideally all other variables are controlled to prevent them from influencing the results - This is harder than it sounds - Example experiment:

    • Variable #1: counting money or blank paper (the IV ) manipulated create two treatment conditions
    • Variable #2: Pain rating ( the DV ) measured in each of the treatment conditions - Nonexperimental studies: - Nonexperimental studies are similar to experiments because they also compare to groups of scores. - Do not use a manipulated participant variable (such as male/female) or a time variable (such as before/after) - The IV is the pre-existing participant variable such as (male or female) or a time variable (before or after) - Example: relationship quality in couples making the transition to parenthood - No manipulation = no causal determinations - Nonexperimental studies example:
      • Variable 1: Subject gender (quasi-IV) - NOT manipulated but used to create 2 groups of subjects
      • Variable 2: verbal test scores (the DV): Measured in each of the two groups

  • Variable 1: Time (quasi-IV) - not manipulated but used to create 2 groups of subjects

  • Variable 2: depression scores (DV) measured of each of the two different times - - Statistical notation:

  • Individual measurement or score obtained will be identified by the letter X ( or X and Y if there are multiple scores for each individual )

  • Number of individuals in data set:

  • N for a population

  • n for a sample

  • Summing a set of values is a common operation in statistics and has its own notation

  • Add them all together: sum

  • Greek letter sigma, Σ, stands for the “sum of"

  • For example ΣX = the sum of all scores on variable X

  • ΣX =76; ΣY= 23. - Order of operations ( PEMDΣAS)

  • P: Calculations within parenthesis are first

  • E- exponents (squaring) are next

  • MD: Multiplying and diving are tied for 3rd and must be completed from left to right

  • 30/5 x 2 + 1 = 6 x 2 + 1 = 12 + 1 = 13

  • Σ - Next is summation with the Σ notation

  • Finally, the remaining adding and subtracting is completed from left to right

  • (6+5)^2 + 5 x 7 = (11)^2 + 35 = 121+35= 156

  • 6 + (5^2 + 5) x 7 = 26 + (25+5) x 7= 6 + 30 x7 = 6 + 210= 216