Bland Altman analysis for triglyceride levels

Figure 1. Output for triglyceride levels

  1. Bland Altman Analysis details (tg0 and tg4)

    The table provides a detailed comparison of two sets of triglyceride measurements, tg0 and tg4. For each pair of measurements, the following statistics are calculated:
    Mean
    The average of the two measurements ((tg0 + tg4) / 2)
    Difference
    The absolute difference between tg0 and tg4 (tg0 - tg4).
    Difference/Mean
    The ratio of the difference to the mean, indicating the relative difference between the two measurements.

    Key observations

    The following observations can be made from the analysis details:
    Positive and Negative Differences
    The differences between tg0 and tg4 vary in direction and magnitude. Positive values indicate that tg0 is higher than tg4, while negative values indicate the opposite. For example, in record 1, tg0 (180) is higher than tg4 (100), resulting in a positive difference of 80. Conversely, in record 9, tg0 (107) is less than tg4 (174), yielding a negative difference of -67.
    Relative Differences (Ratio)
    The Difference/Mean column shows the relative differences between the two measurements. Ratios provide insight into the proportional differences. A higher ratio indicates a larger relative difference. For instance, in record 1, the ratio is .571, suggesting a significant proportional difference, whereas in record 6, the ratio is -.024, indicating a minimal difference between tg0 and tg4.

  2. Confidence Intervals of Mean Differences (tg0 and tg4)

    This table summarizes the mean difference between tg0 and tg4 and its confidence intervals:

    Mean Difference
    The average of all the individual differences between tg0 and tg4 is 14.063. This indicates that, on average, tg0 is 14.063 units higher than tg4.
    95% Confidence Interval (CI)
    The CI of the mean difference is from -10.915 to 39.040, suggesting that the true mean difference between tg0 and tg4 in the population lies within this range 95% of the time. The interval spans both negative and positive values, implying that there is no consistent direction in the difference between the two measurements.
    Ratio (Difference/Mean)
    The mean of the ratios is 0.107, with a 95% CI ranging from -0.083 to 0.297. This suggests that, on average, the differences between tg0 and tg4 are relatively small compared to their mean.
    Interpretation:
    • The wide confidence intervals for the mean difference suggest considerable variability in the differences between tg0 and tg4. Since the CI includes zero, there is no strong evidence that one measurement is consistently higher or lower than the other.
    • The ratio mean difference is close to zero, indicating that, on a relative scale, the two measurements are fairly comparable.

  3. Confidence Intervals of Agreement Limits (tg0 and tg4)

    This table presents the agreement limits and their confidence intervals for both the absolute differences and the ratios:

    Agreement Limits
    • Lower Limit: The lower limit for the differences is -77.812, and the upper limit is 105.937. This means that 95% of the differences between tg0 and tg4 are expected to lie within this range.
    • Ratios: For the ratio of differences to the mean, the lower limit is -0.592, and the upper limit is 0.806. This indicates that 95% of the relative differences between tg0 and tg4 fall within this range.

    Confidence Intervals of Agreement Limits

    For the absolute differences (tg0 - tg4), the confidence intervals for the lower and upper limits are fairly wide, indicating some uncertainty in these estimates:
    • Lower Limit CI: -121.426 to -34.199
    • Upper Limit CI: 62.324 to 149.551
    For the ratios ((tg0 - tg4)/Mean), the CI for the agreement limits also indicates variability:
    • Lower Limit CI: -0.924 to -0.260
    • Upper Limit CI: 0.474 to 1.138
    Interpretation:
    • The wide range of the agreement limits suggests a considerable spread in the differences between the two measurements, indicating variability in the agreement between tg0 and tg4.
    • Since the agreement limits for the ratios are expressed as percentages, the interpretation indicates that in most cases, the difference between tg0 and tg4 does not exceed roughly -59% to 81% of their mean. This variability could be due to proportional differences that vary across the range of measurements.
    • The broad confidence intervals for the agreement limits suggest some uncertainty in the precision of these limits, indicating that the true limits in the population could differ substantially.