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Table 3 Prevalence of correct answers in the intervention ("Int.") and control ("Con.") group, and prevalence ratio of correct answers between the groups, for all respondents and by educational attainment

From: Communicating population health statistics through graphs: a randomised controlled trial of graph design interventions

 

All respondents

Non university-qualified*

University-qualified*

Interventions and interpretation tasks

Int. % (n= 176)

Con. % (n= 187)

Ratio

(95% CI)

Int. % (n= 56)

Con. % (n= 57)

Ratio

(95% CI)

Int. % (n= 116)

Con. % (n= 124)

Ratio

(95% CI)

Interventions: 1. Simplified series labels; 2. Footnote explaining age standardisation (see Figure 1)

Understand the meaning of a point reading of an incidence rate

80.7

57.2

1.4

(1.2–1.6)

76.8

45.6

1.7

(1.2–2.3)

81.9

62.9

1.3

(1.1–1.5)

Understand the influence of age standardisation on comparisons between incidence rates

58.0

36.9

1.6

(1.3–2.0)

42.9

22.8

1.9

(1.1–3.3)

65.5

44.4

1.5

(1.2–1.9)

Interventions: 1. Removed one category from a stacked layer graph; 2. Footnote explaining how to interpret the thickness of a layer (see Figure 2)

For a single disorder, estimate the difference between incidence rates between two age points

57.4

57.8

1.0

(0.8–1.2)

51.8

47.4

1.1

(0.8–1.6)

60.3

63.7

0.9

(0.8–1.2)

Compare an incidence rate reading for a disorder by sex across adjacent graphs

85.2

88.2

1.0

(0.9–1.1)

83.9

82.5

1.0

(0.9–1.2)

87.1

90.3

1.0

(0.9–1.1)

Describe the trend by age along a layer in the graph

69.9

84.0

0.8

(0.7–0.9)

58.9

80.7

0.7

(0.6–0.9)

75.0

86.3

0.9

(0.8 – 1.0)

Broad comparison of the total rate (sum of all layers) within an age range by sex across adjacent graphs

89.2

85.6

1.0

(1.0–1.1)

89.3

87.7

1.0

(0.9–1.2)

90.5

83.9

1.1

(1.0–1.2)

Interventions: 1. Changed a divided bar graph to a side-by-side divided bar graph; 2. Footnote explaining acronyms used in the graph (see Figure 3)

Compare the magnitude of YLL and YLD for a single disease category and sex

65.9

74.9

0.9

(0.8–1.0)

69.6

71.9

1.0

(0.8–1.2)

64.7

77.4

0.8

(0.7–1.0)

Know that YLD represents disability burden and select the disease with the highest value for a single sex

32.4

12.8

2.5

(1.6–3.8)

33.9

10.5

3.2

(1.4–7.5)

31.9

14.5

2.2

(1.3–3.6)

For a single disease, compare the magnitude of YLLs by sex

85.8

88.8

1.0

(0.9–1.1)

83.9

89.5

0.9

(0.8–1.1)

87.9

88.7

1.0

(0.9–1.1)

Select the disease with the highest number of DALYs for a single sex

83.0

67.9

1.2

(1.1–1.4)

80.4

61.4

1.3

(1.0–1.7)

85.3

71.8

1.2

(1.0–1.4)

Intervention: Removed one of three independent variables from the graph so that bars became undivided and there was no need for a legend (see Figure 4)

Read the total rate of YLL for a single geographic category and sex

93.8

80.2

1.2

(1.1–1.3)

89.3

71.9

1.2

(1.0–1.5)

96.6

83.9

1.2

(1.1–1.3)

Broad comparison of the magnitude of YLL rates between two geographic categories, regardless of sex

94.9

90.4

1.1

(1.0–1.1)

94.6

84.2

1.1

(1.0–1.3)

95.7

94.4

1.0

(1.0–1.1)

Broad comparison of the magnitude of YLL rates between sexes, regardless of geographic category

92.6

92.5

1.0

(0.9–1.1)

89.3

84.2

1.1

(0.9–1.2)

94.8

96.0

1.0

(1.0–1.1)

Intervention: Changed a population pyramid to a line graph (see Figure 5)

Broad comparison by sex of the overall population count across a range of age groups, for one geographic area

90.3

78.1

1.2

(1.1–1.3)

85.7

77.2

1.1

(0.9–1.3)

93.1

78.2

1.2

(1.1–1.3)

Broad comparison by geographic region across adjacent graphs of the total population size, regardless of age or sex

78.4

41.2

1.9

(1.6–2.3)

73.2

29.8

2.5

(1.6–3.8)

81.9

46.8

1.8

(1.4–2.2)

Broad comparison of the population size of younger and older segments of the population regardless of region

89.2

85.6

1.0

(1.0–1.1)

83.9

80.7

1.0

(0.9–1.2)

92.2

87.9

1.1

(1.0–1.1)

Interventions: 1. Changed a dot graph with confidence intervals ('hi-lo-close') graph to a bar graph; 2. Footnote providing a simple practical description of confidence intervals (see Figure 6)

Interpret the statistical significance of the difference between two countries of birth in the proportion of premature births

54.5

31.6

1.7

(1.4–2.2)

39.3

15.8

2.5

(1.3–4.9)

62.9

40.3

1.6

(1.2–2.0)

Compare the relative magnitude of the proportion of premature births between two countries of birth represented by adjacent graph bars

91.5

84.5

1.1

(1.0–1.2)

92.9

71.9

1.3

(1.1–1.5)

91.4

90.3

1.0

(0.9–1.1)

Compare the relative magnitude of the proportion of premature births between two countries of birth represented by more distant graph bars

79.5

50.3

1.6

(1.4–1.9)

80.4

35.1

2.3

(1.6–3.3)

80.2

58.1

1.4

(1.2–1.7)

Interventions: 1. Changed the title to a plain question that reflected the intepretation of the graph; 2. Changed some numeric y axis labels to descriptive explanations relating to the title; 3: Removed the footnote that had become redundant (see Figure 7)

Broad judgement of whether Aboriginal people had a higher risk of death than Australians overall

82.4

58.8

1.4

(1.2–1.6)

69.6

38.6

1.8

(1.3–2.6)

90.5

69.4

1.3

(1.2–1.5)

For one age group and sex, read the point estimate of the rate ratio

83.0

55.6

1.5

(1.3–1.7)

69.6

36.8

1.9

(1.3–2.8)

91.4

65.3

1.4

(1.2–1.6)

Understand the meaning of a death rate ratio for one age group and sex

84.7

59.9

1.4

(1.2–1.6)

71.4

42.1

1.7

(1.2–2.4)

92.2

69.4

1.3

(1.2–1.5)

Intervention: Reversed the scale of the vertical axis to represent increasing risk in the upward direction (see Figure 8)

Judge the relative magnitude of risk between the sexes in a single year

79.5

48.7

1.6

(1.4–1.9)

66.1

31.6

2.1

(1.4–3.2)

87.1

58.1

1.5

(1.3–1.8)

For one sex, judge the direction of the trend over time

60.2

20.9

2.9

(2.1–9.9)

62.5

19.3

3.2

(1.8–5.7)

58.6

21.8

2.7

(1.9–3.9)

Read the point estimate of risk for a single sex in a single year

90.9

85.6

1.1

(1.0–1.1)

78.6

77.2

1.0

(1.0–1.4)

97.4

91.1

1.1

(0.9–1.1)

Interventions: 1. Made the y axis ranges on two adjacent graphs match; 2. Slight simplification to the graph title (see Figure 9)

Broad judgment by virus across adjacent graphs of the relative difference in prevalence between the two subgroups

90.9

45.5

2.0

(1.7–2.4)

89.3

35.1

2.5

(1.8–3.7)

93.1

51.6

1.8

(1.5–2.2)

Broad judgement of which subgroup had a lower prevalence of HCV infection

80.7

75.9

1.1

(1.0–1.2)

78.6

66.7

1.2

(1.0–1.5)

81.9

79.8

1.0

(0.9–1.2)

Broad comparison by virus across the two graphs of the prevalence of infection in a single year, regardless of subgroup

92.0

63.6

1.5

(1.3–1.6)

87.5

47.4

1.9

(1.4–2.5)

94.8

73.4

1.3

(1.2–1.5)

Point reading of prevalence of HCV infection for a single year and subgroup

71.0

73.3

1.0

(0.9–1.1)

64.3

63.2

1.0

(0.8–1.3)

74.1

78.2

1.0

(0.8–1.1)

Intervention: Changed the graph type from a vertical bar graph to a line graph (see Figure 10)

Point reading of the proportion of deaths caused by a disease in a single year

83.0

82.9

1.0

(0.9–1.1)

78.6

73.7

1.1

(0.9–1.3)

86.2

88.7

1.0

(0.9–1.1)

Judge which disease had the lowest proportion of deaths in a single year

96.6

94.1

1.0

(1.0–1.1)

96.4

87.7

1.1

(1.0–1.2)

97.4

97.6

1.0

(1.0–1.0)

Judge which disease had the most increasing trend in the proportion of deaths over the period shown

83.5

76.5

1.1

(1.0–1.2)

75.0

56.1

1.3

(1.0–1.8)

89.7

85.5

1.1

(1.0–1.2)

Intervention: Changed a dot graph to a bar graph (see Figure 11)

Judge which sex had the greater proportion for a single injury category

93.8

89.3

1.1

(1.0–1.1)

92.9

78.9

1.2

(1.0–1.4)

94.8

95.2

1.0

(0.9–1.1)

Judge which injury category had the greatest proportion of hospital separations within a single sex

96.0

94.1

1.0

(1.0–1.1)

94.6

89.5

1.1

(1.0–1.2)

97.4

97.6

1.0

(1.0–1.0)

Intervention: Changed the graph type from a pie chart to a horizontal bar graph (see Figure 12)

Identify the category accounting for the largest proportion of cancers in a single sex

97.7

96.8

1.0

(1.0–1.1)

96.4

93.0

1.0

(1.0–1.1)

99.1

100.0

1.0

(1.0–1.0)

Identify the larger of two categories for a single sex

96.6

95.2

1.0

(1.0–1.1)

94.6

93.0

1.0

(1.0–1.1)

98.3

97.6

1.0

(1.0–1.1)

Comparison by sex across adjacent graphs of the contribution of one cancer to all cancers in each sex

95.5

63.6

1.5

(1.3–1.7)

92.9

80.7

1.2

(1.0–1.3)

97.4

56.5

1.7

(1.5–2.0)

Identify the cancer accounting for the smallest proportion of all cancers in a single sex

96.6

90.9

1.1

(1.0–1.1)

94.6

91.2

1.0

(0.9–1.2)

98.3

91.9

1.1

(1.0–1.1)

Point reading of the proportion of all cancers contributed by a single cancer for a single sex

92.0

25.7

3.6

(2.8–4.6)

91.1

40.4

2.3

(1.6–3.1)

93.1

19.4

4.8

(3.4–6.9)

  1. Con., control; DALY, disability-adjusted life year; HCV, hepatitis C virus; Int., intervention; YLD; years of living with a disease; YLL, years of life lost.
  2. *The number of university and non university-qualified participants does not add to the number of all respondents because 2% of intervention participants and 3% of control participants did not report their educational attainment.