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Chapter 10: Problem 9

Researchers in Norway found that of 61,042 children born to women who took folic acid while pregnant there were 64 who developed autism. \({ }^{63}\) This compares to 50 out of 24,134 for women who did not take folic acid. (a) Calculate the sample value of the odds ratio. (b) Construct a \(95 \%\) confidence interval for the population value of the odds ratio. (c) Interpret the confidence interval from part (b) in the context of this setting.

Short Answer

Expert verified
The sample odds ratio is calculated as approximately 1.055. The 95% confidence interval for the population odds ratio is calculated as (approximately) from 0.708 to 1.571. The interval includes 1, suggesting no significant evidence that folic acid affects the odds of developing autism.

Step by step solution

01

Define the odds for each group

Odds of developing autism for children of women who took folic acid is calculated by dividing the number of children who developed autism by the number of children who did not. Same calculation is done for children of women who did not take folic acid.
02

Calculate the odds for each group

For the folic acid group, the odds is 64/60978. For the no folic acid group, the odds is 50/24084.
03

Calculate the sample odds ratio (OR)

The odds ratio is the odds for the folic acid group divided by the odds for the no folic acid group.
04

Calculate the natural log of the OR

Compute the natural logarithm of the OR to simplify the computation of the confidence interval.
05

Calculate the standard error of the log OR

Use the formula for the standard error (SE) of the natural log of the OR.
06

Calculate the 95% confidence interval for the log OR

Multiply the standard error by 1.96 to find the margin of error for the log OR, and then add and subtract this margin from the log OR to find the confidence interval for the log OR.
07

Convert back to the OR scale

Exponentiate the lower and upper limits of the log OR confidence interval to get the confidence interval on the OR scale.
08

Interpret the confidence interval

The confidence interval provides a range of values within which we can be 95% confident that the true population OR falls. If the interval includes 1, this indicates that there is no significant difference in the odds of developing autism between the two groups.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Confidence Interval
To understand the confidence interval, picture it as a range that likely contains the true value of a parameter we're estimating—in this case, the odds ratio. A 95% confidence interval is a range that, if we were to take many samples and calculate an interval from each, we would expect 95% of those intervals to include the true population value. It is formed by taking a sample statistic (like an odds ratio) and adding and subtracting a margin of error.In the exercise presented, the odds ratio is the measure of association between folic acid intake during pregnancy and the odds of developing autism in children. The confidence interval around this odds ratio quantifies the precision of this estimate and helps researchers understand the reliability of the association. If the interval includes 1, it suggests no association—meaning folic acid intake doesn't increase or decrease autism risk significantly. If it's above or below 1, it indicates a possible association.
Epidemiology Statistics
Epidemiology statistics play a crucial role in public health, allowing scientists to investigate the occurrence and control of health-related events in populations. A foundational tool in this field is the odds ratio, which quantifies how the odds of an event (like a disease) in one group compare to another.

Odds Ratio (OR)

The odds ratio particularly shines in case-control studies, where measuring the actual risk or rates is not feasible. The OR helps infer if there's an association between an exposure and an outcome. An OR greater than 1 suggests a positive association, meaning the exposure may increase the odds of the outcome. Conversely, an OR less than 1 implies a negative association, potentially indicating a protective effect of the exposure.In public health, these statistical tools are essential for guiding decisions. For instance, if a study finds a significant odds ratio indicating that a certain exposure is linked to a health outcome, public health officials might consider interventions or policy changes.
Folic Acid and Autism Correlation
The question of whether folic acid intake during pregnancy is related to autism spectrum disorders (ASD) in children is of considerable interest to researchers, healthcare professionals, and families. Epidemiological studies, like the one presented in the exercise, seek to uncover correlations that can inform public health recommendations.It's essential to differentiate correlation from causation. Correlation implies a statistical association between two variables, but it doesn't establish that one causes the other. Various factors contribute to complex conditions like ASD, and isolating the impact of a single factor, such as folic acid intake, requires robust research designs, such as large-scale cohort studies and randomized controlled trials.The study results from Norway suggest that there is an association to be explored further between prenatal folic acid intake and autism. However, establishing a clear causal relationship requires more extensive evidence. As scientists continue to investigate, such findings must be carefully communicated to avoid misinterpretation by the public.

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Most popular questions from this chapter

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