1. PSYC 301
LAB SESSION 5

2. Quick Reminder for Norm Dist Mean and SD

3. Population What we are actually interested in psychology
Example:Interested in the anxiety levels of turkish adults
Although we are interested in the population we look at samples. Why? Why are we not looking at whole population?
It is almost impossible to work with the whole population
Imagine measuring anxiety levels of 58 million people (Number of turkish adults in Turkey)

4. Sample
Purpose of taking a sample is being able to make generalizations about the population WITHOUT testing the whole population
But HOW can a sample, which is usually a very small fraction of the population can produce good results?
With the help of statistics
A sample that can’t be generalized to population is not informative. Relationship between low fat diet and anxiety levels that is shown only for 15 people is hardly interesting for the scientific community

5. Sample
As long as you are taking simple random samples, there is a KNOWN PROBABILITY that your sample mean will be close to the population mean.
Because the MEANS of these SRS will be normally distributed.
WHICH SRS’s?  repeated SRS’s of the same size from the same population
Standard deviation of this distribution is the SEM.
WHICH distribution?  distribution of sample means
WHICH samples? SRS’s
WHAT KIND OF SRS?  SRS’s of same size (n)

6. Demonstration (Simulation)
Simulated data of the turkish adult population scores
Population size=10000

7. Population with 10 samples (N=100)
Red dashed line is the actual pop mean
Thin colorful lines are sample means of N=100 samples.
10 Sample means are shown in this graph

8. Population with 100 samples (N=100)

9. Population with 1000 samples (N=100)

10. Histogram of the sample means (Distribution of Colorful Lines)
Its a normal distribution
SD of this distribution is SEM

11. Distribution of Sample Means And Its properties
Sample means (of the same size) are distributed normally
SD of the sample mean distribution is equal to SEM
Mean of the sample is the best probabilistic estimate of the population mean

12. Excel exercise
Check your s for a mail from me with an excel file attachment
Copy & paste on desktop
Work on it within couples
Finish working on it
the file you worked on back to me with both of your ku usernames
File name:“partner1kuusernamepartner2kuusername LabExcelEx1”
Example “bcavdarogluficoskun LabExcelEx1”
You will lose points if you don’t send your excel file OR if you didn’t work on it