Table 5.

Percentage of responses given for the NS in Studies 1 and 2

		Study 1 (N=259) %	Study 2 (N=190) %
Item 1. Imagine that we roll a fair, six-sided die 1000 times—Out of 1000 rolls, how many times do you think the die would come up even (2, 4, or 6)?
Correct response (500)		78.8	91.1
Errors	Matching error (2, 4 or 6)	9.7	2.1
	Place value error (0.5, 5, 50, 5000)	1.2	2.1
	Mindless multiplication of the numbers in the problem: 3×1000 (3000)	1.5	0.0
	Mindless division of the numbers in the problem: 1000/3 (333.33)	1.5	0.5
	Other errors	6.2	4.2
	No response	1.2	0.0
Item 2. In the BIG BUCKS LOTTERY, the chances of winning a $1000 prize are 1%. What is your best guess about how many people would win a $1000?
Correct response (10)		77.2	88.4
Errors	Place value error (50)	7.7	3.2
	Matching error (1 or 1000)	7.3	6.8
	Other errors	7.3	1.6
	No response	0.4	0.0
Item 3. In the ACME PUBLISHING SWEEPSTAKES, the chance of winning a car is 1 in 1000. What percent of tickets of ACME PUBLISHING SWEEPSTAKES win a car?
Correct response (0.1)		59.8	68.9
Errors	Place value error (0.001, 0.01, 10, 100)	20.1	24.2
	Matching error (1 or 1000)	13.5	4.7
	Other errors	4.6	2.1
	No response	1.9	0.0
Item 4. Which of the following numbers represents the biggest risk of getting a disease? 1 in 100, 1 in 1000, 1 in 10
Correct response (1 in 10)		92.2	98.4
Errors	1 in 100	4.7	1.1
	1 in 1000	3.1	0.5
Item 5. Which of the following represents the biggest risk of getting a disease? 1%, 10%, 5%
Correct response (10%)		93.0	97.4
Errors	1%	4.7	0.5
	5%	2.3	2.1
Item 6. If Person A’s risk of getting a disease is 1% in 10 years, and Person B’s risk is double that of A’s, what is B’s risk?
Correct response (2%)		80.8	91.1
Errors	Divided the number of years by two instead of multiplying the percentage by two (1% in 5years)	7.0	3.7
	Doubled percentage and number of years (2% in 20years)	2.7	0.0
	Other errors	7.6	5.3
	No response	1.9	0.0
Item 7. If Person A’s chance of getting a disease is 1 in 100 in 10years, and Person B’s risk is double that of A, what is B’s risk?
Correct response (2 out of 100)		77.3	88.9
Errors	Divided the number of years by two instead of multiplying the percentage by two (1 out of 100 in 5years)	3.1	2.7
	Mindless division of the numbers in the problem: 100/2 and 10/2 (1 out of 50 in 5years)	2.0	0.5
	Doubled every information in the problem (2 out of 200; 2 out of 200 in 20years)	1.6	0.0
	Other errors	14.8	7.9
	No response	1.2	0.0
Item 8. If the chance of getting a disease is 10%, how many people would be expected to get the disease out of 100?
Correct response (10)		96.5	97.9
Errors	Place value error (1, 100)	1.5	1.6
	Other errors	1.5	0.5
	No response	0.4	0.0
Item 9. If the chance of getting a disease is 10%, how many people would be expected to get the disease out of 1000?
Correct response (100)		93.4	94.7
Errors	Place value error (1)	2.3	1.1
	Matching error (10 or 1000)	1.5	3.7
	Other errors	2.3	0.5
	No response	0.4	0.0
Item 10. If the chance of getting a disease is 20 out of 100, this would be the same as having a ____% chance of getting the disease
Correct response (20)		90.3	91.6
Errors	Place value error (0.2, 2)	3.5	1.6
	Divided numbers in the problem: 100/20	1.2	2.6
	Other errors	4.6	4.2
	No response	0.4	0.0
Item 11. The chance of getting a viral infection is 0.0005. Out of 10000 people, about how many of them are expected to get infected?
Correct response (5)		51.7	81.6
Errors	Place-value error (0.0000005; 0.00005; 0.005; 0.05; 0.5; 50; 500 or 5000)	20.5	9.5
	Other errors	22.8	8.4
	No response	5.0	0.5