ap psych study guides

🤔  Unit 5: Cognitive Psychology

👶  Unit 6: Developmental Psychology

🤪  Unit 7: Motivation, Emotion, & Personality

🛋  Unit 8: Clinical Psychology

1.5 Statistical Analysis in Psychology

#researchmethods

#statistics

#measuresofcentraltendency

#correlation

⏱️  5 min read

written by

Sadiyya Holsey

sadiyya holsey

Dalia Savy

dalia savy

(editor)

September 18, 2020

available on hyper typer

Types of Statistics

Descriptive statistics are numerical data used to measure and describe characteristics of groups, and this includes measures of variation. Therefore, descriptive statistics describe the data📊. 

Inferential statistics provide a way to see validity drawn from the results of the experiment🧪🔬. Inferential statistics tell what the data means.

Summarizing Data

Measures of Central Tendency

Interpreting and constructing graphs📈 and calculating simple descriptive statistics….

The measures of central tendency are median, mean, and mode.  

Median is the middle score of distribution. Mean is the average of a set of scores. Mode is the most frequently recurring score. 

If two scores appear the most frequently, the distribution is bimodal. If three or more scores appear most frequently, the distribution is multimodal.

For example, take this sets of numbers here:

5, 10, 5, 7, 12, 15, 18

The median is the middle of the data set when the numbers are in order so it is 7. 

The mode is 5 because it occurs the most.

The mean is (5 + 10 + 5 + 7 + 12 + 15 + 18)/7 = 10.286

Measures of Variation

Standard deviation is a measure of variability mentioning scores of distribution and the mean. It is used to assess how far the values are spread below and above the mean.

The Z score tells how far a number is below or above the mean in terms of standard deviation. 

Correlation

Correlation coefficient describes how well two variables are correlated. The correlation coefficient ranges from -1 to +1. The closer to -1 or +1, the stronger the correlation.

Positive correlation

Positive correlation shows that as one variable increases ⬆️, the other variable increases ⬆️ For example, a positively correlated group may show that as height increases, weight increases as well.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2Fdownload-13.png?alt=media&token=bb95a3be-9884-48c7-8e84-cbfe957ae8d4

Image courtesy of Expii.

Negative correlation

Negative correlation shows that as one variable increases ⬆️, the other decreases ⬇️. An example of a negative correlation could be how as the number of hours of sleep increases, tiredness decreases.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2Fdownload-14.png?alt=media&token=0899f19d-4cb3-458d-9359-b7a19bc80df4

Image courtesy of Expii.

No correlation

No correlation shows that there is no connectionbetween the two variables. An example of no correlation could be IQ and how many pairs of pants an individual owns.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2Fdownload-15.png?alt=media&token=7a1e00b9-9bf9-4075-ac51-987eca2558ad

Image courtesy of Expii.

Remember, correlation does not imply causation. You must run an experiment to prove there is causation.

Skews

Frequency distribution is a breakdown of how the scores fall into different categories or ranges. Normal distribution shows how traits are distributed throughout a population usually with the use of a bell 🔔 curve. 

There are also positive skews👍 and negative skews👎. Graph a below is positively skewed (aka skewed to the right) because the direction of the skew is going in a positive direction. Letter c is negatively skewed (aka skewed to the left) because the direction of the skew is pointing in the negative direction.

It might be hard to remember which way the skew is. If the tail on the right is longer, like it is in a, then it's a skew to the right. If the tail on the left is longer, like it is in c, then it's a skew to the left.

When the distribution is skewed to the right, the mean is greater than the median. When the distribution is skewed to the left, the median is greater than the mean.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2Fdownload-16.png?alt=media&token=92523fe9-7f53-40cb-9567-9b3b3feced23

Image courtesy of ResearchGate.

Normal

The normal curve, or (b) in the above image, is the only one you have to really be familiar with for this course. There are two important values that you should memorize: 68% and 95%.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-xauuB3tV4Qxt.JPG?alt=media&token=62d153c3-7b7b-4ce2-af0a-fa8df2f78970

Image from Myers' AP Psychology Textbook; 2nd Edition

This is a normal curve that includes data about intelligence📖. Basically, 68% of the data falls within one standard deviation about the mean. Here, one standard deviation is equivalent to 15, so the data falls between 85 and 115, or +- 15 points of 100.

95% of the data falls within two standard deviations about the mean. Since 2 standard deviations is equal to 30, the data falls between 70 and 130, or +-30 points of 100.

Another term that you should be somewhat familiar with is statistical significance, or the likelihood that something occurs by chance😲. If something is statistically significance, it did not occur by chance (some outside factor influenced the data). If something isn't statistically significant, it occurred completely by chance. To determine this, you would compare the mean of the control group and the mean of the experimental group.

Practice FRQ

The following question is taken from the College Board website (2017 AP Exam - Part B of #1).

A study was conducted to investigate the role of framing on concern for healthy eating🍏. Each participant (N = 100) was randomly assigned to one of the two conditions. In the first condition, the participants read an article indicating that obesity is a disease🦠. Participants in the second condition read an article indicating that obesity is the result of personal behaviors and decisions.

Participants were asked to indicate how important it would be for them to eat a healthy diet. Scores ranged from 1 (not very important) to 9 (very important). The results are presented in the table below.

Group

Mean Score - Concern for Healthy Eating

Standard Deviation

Disease

3.4

1.4

Behavior

6.1

1.2

Table Courtesy of College Board

  • Operationally define the dependent variable.

  • What makes the study experimental rather than correlational?

  • What is the most appropriate conclusion the researchers can draw about the relationship between the variables in the study? 

The scoring guidelines provide the rubric for this question. You should be able to answer all three parts. If not, just go through this unit’s guides one more time and you’ll nail this FRQ.

🎥Watch: AP Psychology - Statistics in Psychology

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