Quiz: Garlic prawns

The following quiz assesses students' ability to critically think about a piece of research.  The study looks at the role of cognitive biases on restaurant ordering.

To assign this quiz to your students, please go to the student page for this quiz.

If you would like to give them a paper copy, please see the link below.

Student copy

The quiz

Crane (2021) wanted to see how exposing restaurant customers to an anchor might affect how much money they were willing to spend on dinner. 

To carry out his study, he worked together with a local Italian restaurant. The study took place over two consecutive Friday nights in May 2021. On the first night, the researcher had the waitstaff offer “today’s specials” to the customers.  The specials were announced as the waiter was handing out menus. 

The waitstaff said: Tonight, we have a wonderful special as a main course – garlic prawns (shrimp) and spaghetti for $38.50.

This is a rather high price for this dish!   The researcher wanted to see if this would serve as an anchor when choosing a main course.   On the following Friday night, no special was mentioned. 

At the end of the evening, the researcher found the average price paid for the main course.  He found that on the first night, the average cost of the main course was $24.30; on the second Friday night the average cost was $18.20.  No one chose the “special.” It appears that by mentioning the price of the “special,” people were willing to spend more money on their Friday meal.


  1. Which design was used in this study?  What was the independent and dependent variable?
  2. Comment on the internal validity of this study.
  3. Explain how one potential participant variable may have affected the study.
  4. Explain one ethical consideration in this study.
  5. Comment on the ecological validity of this study.
  6. Comment on the construct validity of this study.

Assessing responses

Each of the responses may earn up to a maximum of three marks, for a total of 18 marks.

1. Which design was used in this study?  What was the independent and dependent variable?

Sample student response: The study uses an independent samples design. The independent variable is whether the customers are told a special for the evening with a high price which serves as an anchor. The dependent variable is the amount of money spent on the main course.

Assessment: 1 mark for correctly identifying the design. 1 mark for identifying the IV.  1 mark for identifying the DV.

2. Comment on the internal validity of this study.

Sample student response: This experiment is being done "in the field" so the internal validity is to some extent compromised. However, there is a control group to compare to the "anchor group."  In addition, the researcher manipulates the IV and the two conditions are done on two separate evenings to avoid the problem that customers may hear the special who are in the control group. However, there is no control over extraneous variables or participant variability which means that it is difficult to say that the anchor alone caused their choice of food.

Assessment: 1 mark for a definition of internal validity. 2 marks for a clear justification of their position linked directly to the study.

Common errors: A common error is to say that this is a field experiment so it has "no internal validity."  This is not correct. The goal of the "comment" command term is for students to show that it is not a "yes" or "no" response - but that these concepts are complex.

3. Explain how one potential participant variable may have affected the study.

Sample student response: There are several potential confounding variables, but participant variability is a rather important one.  Participant variables may include whether they have dietary limitations (e.g. allergic to garlic, trying to lose weight, or don't like prawns), whether they are a regular at the restaurant and have a favourite dish they always order, or their socioeconomic status.  If they are worried about money, then this will be the reason that they choose the dish that they do, rather than because of the anchor.  Each of these participant variables may compromise the internal validity of the study and not allow for a causal relationship to be determined.

Assessment: 1 mark for understanding the term "participant variable." 1 mark for identifying an appropriate participant variable. 1 mark for explaining how it may impact the study. Other appropriate variables include whether they like the waiter or not or the individuals' level of hunger when they order.

Common errors: Participant variables are one type of confounding variable. Some students may write about situational variables (e.g. the number of people sitting at the table and their potential effect on what is ordered) or demand characteristics.  Although these are both confounding variables, they are not participant variables.

4. Explain one ethical consideration in this study.

Sample student response: One ethical consideration in this study is deception by commission. The waitstaff presented an unreasonable "special" to the customers to potentially manipulate how much money they would spend on their meal. This deception is problematic because the customers do not realize that they are part of an experiment.  Secondly, it may lead to them spending more money than they normally would have - and this could be problematic.  However, the researcher would have to debrief the customers at the end of the evening so that they were aware of what had happened and would have the right to withdraw their data.  A good researcher would also offer everyone in the experiment a drink or dessert to make up for the extra money spent.

Assessment: 1 mark for identifying and defining an ethical consideration. Up to 2 marks for linking the ethical consideration to the study.

Common errors: Many students like to gravitate to "undue stress or harm." Although the anchor may influence people's choices, if a person really does not have the money to spend, they will not be "financially harmed" by this experiment. Such responses are superficial and do not attract high marks.

5. Comment on the ecological validity of this study.

Sample student response: This study is a field experiment - which means that it takes place in the participants' naturalistic environment.  All of the customers at the restaurant clearly chose the restaurant, so they must like the type of food that is offered.  In addition, the situation of having a waiter announce tonight's specials is not an artificial experience.  The ecological validity of the study is very high as the situation is not highly controlled or artificial - meaning that the findings can be generalized to similar situations.  Most likely the use of anchors can affect one's choice of food from a menu.

Assessment: 1 mark knowledge of the meaning of ecological validity. Up to 2 more marks for a clear link to the study.

Common errors: Students often write that the sample is representative or not - and that this affects the ecological validity.  This is incorrect.  This affects the external validity - which is based on both ecological and population validity.

6. Comment on the construct validity of this study.

Sample student response: The researchers want to know whether the anchor actually affects the choice of food. It is impossible to know exactly why the participants chose the food that they did and whether it was actually the anchor that made a difference.  This is one of the limitations of research on thinking and decision-making - we cannot directly observe one's thinking and people are not good at explaining their choices. Therefore, we cannot know if we are actually measuring the effect of the anchor or some other variable, compromising the construct validity.

Assessment: 1 mark for a definition of construct validity (or a clear indication of understanding). 1 mark for identifying the variable that may have or lack construct validity. 1 mark for an explanation of why this variable may lack or have construct validity. Other potential responses would focus on the use of the price of the main course as the dependent variable.  This is well operationalized because if the whole meal were the DV, there would be too many potential variables - e.g. whether they drink alcohol with their meal, whether they want dessert, coffee, etc.

    Suggested markbands

    7: 16 - 18

    6: 14 - 15

    5: 11 - 13

    4: 9 - 10

    3: 7 - 8

    2: 5 - 6

    1: 0 - 4

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