Essential Questions

• EQ 1-5: How do psychologists draw appropriate conclusions about behavior from research?

Do Now:

• Take the 3 handouts, and go over your homework with your table. Make sure you all agree on the answers!

The Science of Psychology

Approaches to Psych

Growth of

Psych

Research

Methods Statistics

Descriptive Correlation Experiment

Case Study

Survey

Naturalistic Observation

Descriptive Inferential

Ethics

Sampling

Central Tendency Variance

Careers

We are

here

Why do we need statistics in psych?!

• Descriptive Statistics: – Central Tendency 

• Mean, median, and mode• skewed distributions

– Variance • Range• standard deviation• normal distributions

• Inferential Statistics:  – Statistical significance

• t-test and the p-value

Statistical procedures analyze and interpret data and let us see what the

unaided eye misses.

Central Tendency

• Tendency of scores to congregate around some middle variable

• A measure of central tendency identifies what is average or typical in a data set

Measures of Central Tendency

Mode: The most frequently occurring score in a distribution.

Mean: The arithmetic average of scores in a distribution obtained by adding the scores and then dividing by their number.

Median: The middle score in a rank-ordered distribution.

Practice:

What is the mean, median, & mode of the following distribution:

1, 6, 3, 12, 8, 11, 9, 10, 4, 6

Normal Distributions

•The distribution of data also gives us key info.

•We know that many human attributes…

•e.g height, weight, task skill, reaction time, anxiousness, personality characteristics, test data, attitudes, birthdays, etc.

•…follow a normal distribution.

Practice:

• Imagine that you are a golfer of above-average ability and that you have the opportunity to play the greatest golfer in the world (say Tiger Woods). If you want to maximize your slim chance of winning, how much golf would you elect to play, given the choices of 1, 18, 36, or 72 holes?

• A certain town is served by two hospitals. In the larger hospital about 45 babies are born each day, and in the smaller hospital about 15 babies are born each day. Although the overall proportion of boys is about 50 percent, the actual proportion at either hospital may be greater or less than 50 percent on any day. At the end of a year, which hospital will have the greater number of days on which more than 60 percent of the babies born were boys?

• (a) the larger hospital• (b) the smaller hospital

• (c) neither--the number of days will be about the same (within 5 percent of each other)

Negatively Skewed

                

Positively Skewed

Central Tendency

$25,000-Pam $25,000- Kevin$25,000- Angela$80,000- Jim$100,000- Andy$100,000- Dwight$300,000-Michael

Let’s look at the salaries of the employees at Dunder Mifflen Paper in Scranton:

The median salary looks good at $80,000.The mean salary also looks good at about $93,500.But the mode salary is only $25,000.Maybe not the best place to work.Then again living in Scranton is kind of cheap.

The mean doesn’t work in a skewed distribution

The Median is much better

• Descriptive Statistics: – Central Tendency 

• Mean, median, and mode• skewed distributions

– Variance • Range• standard deviation• normal distributions

• Inferential Statistics:  – Statistical significance

• t-test and the p-value

18

Two Measures of Variation

Range: The difference between the highest and lowest scores in a distribution.

7, 98, 46, 38, 54, 78, 9, 5, 45, 23

• Standard Deviation: the variance of scores around the mean.

• The higher the variance or SD, the more spread out the distribution is.

• Do scientists want a big or small SD?

Shaq and Kobe may both score 30 ppg (same mean).But their SDs are very different.

Normal Distribution

21

Standard Deviation in Action• A couple needs to be within one standard

deviation of each other in intelligence (10 points in either direction). —Neil Clark Warren, founder of eHarmony.com

Normal Distribution

Practice Prob:

• What is the standard deviation for the numbers: 75, 83, 96, 100, 121, and 125?

• Descriptive Statistics: – Central Tendency 

• Mean, median, and mode• skewed distributions

– Variance • Range• standard deviation• normal distributions

• Inferential Statistics:  – Statistical significance

• t-test and the p-value

Inferential Statistics

• You are trying to reach conclusions that extend beyond just describing the data.

• Inferential stats allow us to apply the research data to the entire population, not just the sample. I can apply RHS data to all high school students in the US. ONLY USED WITH EXPERIMENTS (CAUSE & EFFECT)

•Does caffeine improve our reaction time?

•We recruit 40 people and give (random assignment)

»20 a caffeine pill (experimental group)

»20 a sugar pill (control group)

•We give them a brief reaction time test and record the results.

•Yes, group results are different. . .

Why can’t I be done?!

• You don’t know if that difference was due to your IV (caffeine) or just dumb luck.

• You have to be sure that the results are statistically significant

Statistical Significance*You can never 100% fully prove anything in science, because you can never know if it was 100% not due to chance *You can only reject the null hypothesis, which is the opposite of your hypothesis *Statistical Significance: Means that the results of the experiment were most likely NOT due to random CHANCE/dumb luck. p-value < .05%*(never a 0% p-value) BUT if the p-value is less that .05%, you can be confident enough to disprove null hypothesis (statistically significant)

T-test results•Does caffeine improve our reaction time?

•Caffeine condition has a lower mean RT.

•We run a t-test on our samples and get:

»p = 0.039

•Can we be confident that the difference in the data is not due to chance?