Charting: Follow-up BFN/BFP Stats Study

We recently published a more detailed study as a site FAQ following the comments that I mention below:
Early Negative Pregnancy Test Before a Positive - Stats Study

First I'd like to thank all members who took the time to send their comments and feedback. It was, as usual, very interesting and insightful. I will summarize the comments below.

The main comment was that people recognize themselves in the numbers and found a validation of their personal experience.

Concerning the early positive results, most people pointed out that there are now very sensitive tests and that helps to explain the results we see. This is a valid point which can easily be seen in the stats published in the HPT Photo Gallery.

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Charting: Negative Pregnancy Test Before A Positive

When seeing an early negative test result, most people wonder if they could still be pregnant and if they might test positive later on in the cycle. If a negative test was taken too early, the answer is most definitely, yes (Check the Chart Gallery for numerous examples) however it is still interesting to look at some statistical data about these pregnancy test results.

To explore the issue of the reliability of early pregnancy tests, we looked at just under 6000 charts for which a negative pregnancy test was followed by a positive test and did not result in a miscarriage.

First Negative Pregnancy Test Before Positive

Average: 9.08 DPO
Median: 9 DPO

First Positive Pregnancy Test After Negative

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Charting: Temperature Rise and Pregnancy - Stats Study

Among the numerous feedback we received, a few interesting issues were raised. I'd like to discuss it below.

Lopsided Histograms
Some readers, well trained in stats, noticed that the histograms departed from the normal distribution which can skew any test of hypothesis that would assume a normal distribution. One reader suggested to run a Kolmogorov-Smirnov test instead of the simple t-test that we ran. I just did that but unfortunately it was again not really conclusive (p value of 0.16).

Temperature Scaling
Some readers pointed out that comparing temperatures may not be the best because everyone has a different metabolism. They suggested to compare the difference between pre-ovulation and post-ovulation temperatures instead. We ran a study to measure the temperature rise.

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Charting: Average Temperature After Ovulation - Stats Study

We looked at the average temperature between 1 and 10 Days Past Ovulation (DPO). The reason for looking particularly at this phase of the cycle is that we often see people looking at their average post-O temperatures as a potential early pregnancy sign.

For this study we have randomly selected a set of 1000 pregnancy charts and 1000 ovulatory charts (see the Chart Gallery for examples). For each chart we calculated the average temperature between 1 and 10 DPO.

The histogram below shows you the distribution of temperatures (in Fahrenheit) for pregnancy charts:

The histogram below shows you the distribution of temperatures (in Fahrenheit) for ovulatory charts:

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Charting: Follow-up - Seasonal Variations of Temperature (BBT)

Data Sample

Many members were concerned that the data sample may include people in the southern hemisphere which may skew the data. Let me put this concern to rest, the data presented only included data from the United States. It does not include data from the southern hemisphere. We also considered a larger data set and saw similar patterns. To avoid any possible confusion we decided to present only a restrictive subset.

Some members feared that we did not have enough data to show a significant plot and that a few people with abnormal temperatures may have skewed the data. The data set includes only a subset of the data we have available in order to run the calculation quickly. It however includes several hundreds of thousands of data points per months.

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Site News: New on Tickerfactory.com

Check them out: TickerFactory.com

New Rulers and Sliders
With the introduction of the new tickers we have added a few new designs of rulers and sliders.

Weight Ticker New Features
We have added new features to the weight ticker on tickerfactory.com- worth mentioning for those tracking their weight loss:

• Weight Graph: you can now see your weight loss progress on a clean graph and on your own weight loss page.
  
• Body Mass Index. The ticker is now capable of calculating and displaying your body mass index.
  
• PIN protection to keep your data while still having the convenience of no extra registration.
  

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