Question

Recall again that Rind & Bordia (1996) investigated whether or not drawing a happy face
on customers’ checks increased the amount of tips received by a waitress at an upscale
restaurant on a university campus. During the lunch hour a waitress drew a happy,
smiling face on the checks of a random half of her customers. The remaining half of the
customers received a check with no drawing (18 points).
The tip percentages for the control group (no happy face) are as follows:
45% 39% 36% 34% 34% 33% 31% 31% 30% 30% 28%
28% 28% 27% 27% 25% 23% 22% 21% 21% 20% 18%
8%
The tip percentages for the experimental group (happy face) are as follows:
72% 65% 47% 44% 41% 40% 34% 33% 33% 30% 29%
28% 27% 27% 25% 24% 24% 23% 22% 21% 21% 17%

This time, you are to perform a “hypothesis test” using the tip data, answering each of
the questions below. For short-answer questions, be brief. However, you must give
enough detail to justify your answers. Single-sentence responses will generally not
suffice, but do not exceed a paragraph for any given answer.

o. Considering both the probability value and effect size measure, what
interpretations would you make about the findings? That is, what are your
conclusions about the effects of leaving happy faces on checks?

Answer 1

Here we have two independent samples. We need to check whether tip percentages increases if drawing a happy face.

Let group 1: control group

Group 2: experimental group

Hypotheses are:

Following is the output of independent sample t test:

The t test statistics is

t = -1.55

The p-value is: 0.0651

Since p-value is greater than 0.05 so we reject the null hypothesis. That is we can conclude that drawing a happy face
on customers’ checks increased the amount of tips received by a waitress at an upscale restaurant on a university campus.

Effect size:

Pooled standard deviation is :

So,

Effect size is medium.