Communicating t-test Results

General Question:  Your employer says, I think men take more sick days then women in this company, and we need to do something about it.  Let me know what the stats are.

Research Question:  Is there a significant difference between the average number of sick days taken by men and women in the past 12 months?

Hypotheses:  There IS NO significant difference between average number of sick days for men and women during the past 12 months (Null Hypothesis).  There IS a significant difference between average number of sick days for men and women during the past 12 months (Alternative Hypothesis).

Analysis Plan: Because the research question is about differences between two averages, Male and Female average sick days, the Independent groups t-test is the best statistic to use.

For more on how to pick the best statistical test please visit:

http://www.ats.ucla.edu/stat/mult_pkg/whatstat/

Calculate Statistic: Calculate the average number of sick days for male and female employees using IBM SPSS.  Use the Independent Groups t-test to determine if the difference between the average Male and Female sick days is significant.

Compute Probability:  When the results of the t-test show that the null hypothesis has less than a 1% chance of being right, we reject it and suggest the alternative hypothesis is worth considering.

For more on the concept of the p-value please visit:

http://askville.amazon.com/explain-concept-p-value-simple-English/AnswerViewer.do?requestId=6438921

Communicate Results like a Statistician:

Mr. Boss, we used an Independent groups t-test to determine if there is a significant difference in the average number of sick days taken by male and female employees in the past 12 months. You will be happy to know that the results were: t=-3.7341(198), p<.01 and the results were significant.  Therefore we rejected the null hypothesis. 

Therefore there IS a significant difference between the average sick days for men (50.1) and the average sick days of women (54.99) in the past 12 months.  

Women in this company took more sick days than men in the past 12 months.

IBM SPSS Output for Independent Groups t-test:

IBM SPSS t-test Output

IBM SPSS t-test Output

To learn more about the t-test used in this article please visit:

http://www.ats.ucla.edu/stat/spss/output/Spss_ttest.htm

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s