EBVs of different animals can be directly compared with each other, but how do they compare to the rest of the sheep in NSIP? The Percentile Report, generated by NSIP, is a tool that allows you to evaluate individual animals, set breeding goals, help with marketing and sales, as well as to understand what is available in the breed. As a producer you need to know how to read the Percentile Report, explain it to customers and know what data goes into calculating the percentiles.
Note: This article uses the NSIP Katahdin Percentile Report that was generated on 12/18/2024.
Percentile
A percentile shows where an EBV value ranks compared to the rest of the EBV values for that specific EBV, expressed as a percentage. Think of it like lining up all the sheep from lowest to highest for a particular EBV. If your sheep is at the 80th percentile, it means it’s standing at the 80% mark in that line, with 80% of sheep behind it and 20% ahead of it. This gives you a clear picture of how your animal compares to all other sheep for that EBV. For example, if your ram has a weaning weight at the 90th percentile, you know it ranks higher than 90% of all other sheep for that EBV.
Note: A later section will describe which specific animals are used in the percentile calculation.
In the context of the Percentile Report, the 100th percentile represents “maximized” and the 0th percentile represents “minimized” while the 50th percentile represents the median (the mid-point, 50% have more and 50% have less).
Note: The 50th percentile is not the average, the 50th percentile might be close to the average but it does not have to be.
I use the terms “maximized” and “minimized” rather than “largest” and “smallest” because the direction varies by EBV. For example, for maternal weaning weight (MWWT), a higher value represents more milk potential – moving towards “maximized” means increasing the EBV value. However, for post-weaning fecal egg count (PFEC), a lower value represents greater parasite resistance – moving towards “maximized” means decreasing the EBV value. In both cases, the 100th percentile represents the extreme value for that EBV, regardless of whether it’s numerically larger or smaller than other values. This is sometimes called Percentile Directionality.
Note: All of the EBVs on the Percentile Report have larger values at “maximized” except for PFAT, WFEC and PFEC that all have smaller values at “maximized.”
Percentile Report Uses
Evaluating Individual Animals
By looking up the percentile ranking of each EBV for an animal you can quickly assess where that animal ranks within the population. This allows you to assess which EBVs the animal is particularly strong or weak in.
The percentile values put EBVs in context:
- Ram A has a NLB of 0.11 and Ram B has a NLB of 0.15, there’s only a 0.04 difference in NLB, is this a big difference? Ram A is in the 50th percentile while Ram B is in the 75th percentile. Yes – Big difference.
- Ram A has PWWT of 2.76 and Ram B has PWWT of 2.80, there’s a 0.04 difference in PWWT, is this a big difference? Ram A is in the 50th percentile and Ram B is in the 50th percentile. No – Not a big difference.
Note: You might wonder why I say Ram B is in the 50th percentile if its PWWT is larger than the 50th percentile band. Later I will explain how you should approach doing percentile lookups.
Setting Breeding Goals
Each producer needs to determine what range of EBVs work for them and/or their breeding stock customers. Remember that maximized, minimized, or median percentile values are not always the optimal choice.
Start by analyzing your current position:
- Review your Genetic Trend Report from your data run output or analyze your own EBV data
- Determine the percentile ranking of your average lamb for each EBV
- Compare where you are to where you want to be
When evaluating your flock’s percentile rankings, consider:
Understand Your Position
- Are there EBVs at extreme percentiles (high or low) that you hadn’t noticed?
- Have you been actively selecting for this position, or did it happen unintentionally?
Evaluate Your System
- Do your percentile rankings align with your production goals?
- Example: A low NLB percentile might be fine if you’re happy with your current lambing rate, but problematic if you want higher productivity
Consider Market Demands
- Do your genetics match what your customers need?
Setting goals in terms of percentile values have the following advantages:
- Percentile values help you understand how achievable goals are
- It simplifies making tradeoffs between multiple EBVs because they are all on the same scale, 0th percentile to the 100th percentile
- Helps avoid overemphasizing single EBVs by keeping all EBVs on the same scale
- Makes it easier to understand what’s exceptional versus typical
- Makes long-term breeding goals more meaningful and consistent
Marketing and Sales
Marketing in terms of percentile values provides more objective information that is easier for a customer to understand and relate to. It helps customers understand how an animal compares to the broader population of sheep in NSIP which in turn supports price decision making based on genetic merit.
Understanding the Breed
By studying the Percentile Report you can get a better understanding of the genetic merit that is available in the breed, what is typical and what is exceptional. This provides context that will help you select, set goals and market animals.
Percentile Report
You can access the Katahdin NSIP Percentile Report by navigating to http://nsipsearch.nsip.org/ and then clicking on (1) “Reports” followed by clicking on (2) “Katahdin.”
There are five major sections on the Percentile Report as indicated in the above image (each one is marked with a rectangle and a number).
- Header
- Percentile Bands
- EBV Percentile Values
- Report Footer
- Record Summary
Header (1)
The header section contains the headings for the various columns. The first column “Percentile” is the percentile band column. The rest of the columns are EBVs or Indices.
Percentile Bands (2)
Percentile Bands list the percentiles for which EBV Percentile Values are calculated. Not all possible percentiles are listed. The top starts with 100 (the 100th percentile), 99, … down to the 0th percentile at the bottom. The Percentile Bands are graduated, more detailed information is provided closer to the 100th percentile while less detail is provided as you get closer to the 0th percentile at the bottom.
Note: You might be tempted to guess the percentile value if it falls between two percentile bands, don’t do it unless you have access to all the data that went into the calculation of the original percentile bands. You don’t know how values change (or are shaped) between two percentile bands. A later section will provide more detail.
EBV Percentile Values (3)
This section lists the EBV Percentile Values for specific EBVs that correspond to specific Percentile Bands.
The image above shows that the 95th Percentile (Percentile Band) for PFEC (EBV) starts at -89.08 (EBV Percentile Value).
Report Footer (4)
The Report Footer is at the bottom of the report and shows the units that each EBV is measured in (the Units row) as well as the number of animals (the Number of Lambs row) that were included when the EBV Percentile Values were calculated.
Note: PSC and HWT included zero lambs in the calculation of the percentile values and all the percentile values for these EBVs are zero because the percentiles are not currently calculated.
Note: Looking at the footer you will notice that the number of animals included in the percentile calculation is not the same for all EBVs. That is because the criteria for the animals to include vary by EBV category. See Percentile Report Data section later in this document.
Record Summary (5)
The Record Summary section shows general data about the data in the NSIP Searchable Database.
- Total Katahdin Records: How many Katahdin sheep are in the database
- 2023-2024 Born Lambs: How many lambs were born total in 2023 and 2024
- 2023-2024 Lambs with Linkage: How many lambs were born in 2023 and 2024 that have linkage for Weight category EBVs
- 2023-2024 Born Ram Lambs: How many ram lambs were born in 2023 and 2024
- 2023-2024 Born Ewe Lambs: How many ewe lambs were born in 2023 and 2024
What is Linkage?: You might wonder what “Linkage” means. It is a flag (true / false value) for each animal to indicate if that animal is eligible to receive across-flock EBVs for various EBV Categories.
EBV Categories Linkage Flags:
- LINKED_WT (Weight): MBWT, BWT, MWWT, WWT, PWWT, YWT and HWT
- LINKED_FEC (Fecal Egg Count): WFEC, PFEC
- LINKED_CAR (Carcass Ultrasound Scanning): PFAT, PEMD
- LINKED_REP (Reproductive): NLB, NLW
Note: The linkage flags listed above can be found in the raw data that you download from Sheep Genetics.
Animals that do not have Linkage typically have EBV values on the Individual Listing but there is no accuracy. These values show as zero on the NSIP Searchable Database even though they have different values on your Individual Listing.
Animals that do have Linkage with insufficient accuracy for that EBV category will not have EBV values on the Individual Listing. These values show as zero on the NSIP Searchable Database.
Animals that do have Linkage with sufficient accuracy will show EBV values and accuracy on the Individual Listing. These values and accuracies should display on the NSIP Searchable Database.
Percentile Report Lookup
Data Representation
There’s a difference in how some EBV values are displayed between the Individual Listing and the Percentile Report. For NLB and NLW the Individual Listing displays the EBVs as a percentage while the Percentile Report displays it as a decimal value. The image above shows NLB as 12% in the Individual Listing and as 0.12 as a decimal representation in the Percentile Report. Keep this in mind when doing percentile lookups.
EBV Directionality
| Not all EBVs have the same directionality. Most EBVs have the largest number at the 100th percentile and the smallest number at the 0th percentile (Ascending order). PFAT, WFEC and PFEC have the smallest number at the 100th percentile and the largest number at the 0th percentile (Descending order). You need to keep this in mind when reading the Percentile Report. |
Extreme Values
When looking up percentiles you might encounter instances where the value is above the 100th percentile or below the 0th percentile. This can happen because the animal you are looking up is not included in the data that is used to calculate the percentile bands (see Percentile Report Data below for more detail), or the Percentile Report has not been updated since the younger animal had its EBVs updated.
Look at 6401552014141615 (shown above in the NSIP Searchable Database above) you can see that the animal has a MWWT of 2.791.
The 100th percentile band for the current percentile report is 2.49 (as shown above) for MWWT.
What percentile is the MWWT percentile of 6401552014141615? 100th percentile.
Percentile Value Lookup
You can look up percentile values by hand using the Percentile Report or you can view the Trait Chart on the Details page of the NSIP Searchable Database that automatically displays the percentile values for an animal.
Manual Percentile Value Lookup
| MWWT: The ewe above has a MWWT value of 0.600 and we know that MWWT is in Ascending order (Higher percentile values have higher EBV values). Think of the Percentile Report like a ladder, with MWWT bands from 0 to 100. Here’s how to find where this MWWT value fits: 1. Start at the bottom (0th percentile) 2. If the MWWT is less than the 0th percentile value, then it’s in the 0th percentile 3. Move up the ladder, checking each band (0, 10, 20, etc.) until you find your exact number, or the first value larger than your MWWT. 4. If your MWWT perfectly matches the percentile value, then that is the percentile band that it falls in. 5. If the value is larger than your MWWT, your percentile band is the one just below it. 6. If the MWWT is larger than the 100th percentile value, then it belongs in the 100th percentile. The ewe has a MWWT in the 50th percentile |
WFEC: The ewe above has a WFEC of -83 and we know that WFEC is in descending order (Higher percentile values have smaller EBV values). Here’s how to find where the WFEC value fits when an EBV is in descending order:
- Start at the bottom (0th percentile)
- If the WFEC is larger than the 0th percentile value, then it’s in the 0th percentile
- Move up the ladder, checking each band (0, 10, 20, etc.) until you find your exact number, or the first value smaller than your WFEC.
- If your WFEC perfectly matches the percentile value, then that is the percentile band that it falls in.
- If the value is less than your WFEC, your percentile band is the one just below it.
- If the WFEC is less than the 100th percentile value, then it belongs in the 100th percentile.
The ewe has a WFEC in the 95th percentile.
Automatic Percentile Value Lookup
A Trait Chart is displayed when you view the detail of an animal in the NSIP Searchable Database. The Trait Chart for an animal is displayed below, in this example it is a different animal from the one used on the Manual Percentile Value Lookup.
On the x-axis (the horizontal) is the percentile scale, 0th percentile (left) to the 100th percentile (right). On the y-axis (the vertical) we have various EBVs listed. You can move your mouse cursor over the bar for a specific trait to display a tooltip with the actual percentile value (In the example above the mouse was over WFEC).
The percentile bands used by the Trait Chart are a bit different from the Percentile Report but still based on the same data. Lower percentile ranges (below the 70th percentile has more detail in the Trait Chart; it is displayed in increments of 5 at lower ranges).
Generally speaking, only traits with an accuracy higher than 0 are listed on the y-axis. The exceptions to this are MWWT, PFAT, US Hair Index and SRC$ Index. Only EBVs that are displayed on the Details page will be considered for display on the Trait Chart.
Percentile Report Data
The data used in the Percentile Report vary by EBV category, that is why the Report Footer shows different totals for “Number of Lambs” (the row indicating how many animals were included in the percentile calculation for that EBV).
Common Criteria
The common criteria to decide which animals to include in the percentile calculation:
- NSIP Id starts with 640 (Katahdin)
- Must have a date of birth in 2023 or 2024 (or more generally, born the last two years)
- Have a STATUS of “CURRENT” or “SOLD”
Note: The first updated percentile report of 2025 will have fewer animals because it looks at the last two years not the last 24 months. As 2025 born lambs are added through the year, the numbers gradually increase closer to the current population.
Note: The STATUS criteria was unexpected. At the end of a year, we typically mark all our animals sold for meat (majority of our lambs) as DEAD or CULL. The result of that is that most of our lambs are not included in the percentile calculation.
Note: About 19% of 2023 / 2024 born Katahdin animals are excluded from the percentile data because the STATUS does not match “CURRENT” or “SOLD”.
EBV Category Criteria
In addition to the Common Criteria, there are additional criteria applied to decide which data to include in the percentile calculation which varies by EBV Category.
- MBWT, BWT, MWWT, WWT, PWWT, YWT and US Hair Index: Weight Category EBVs need to have weight linkage (LINKED_WT)
- PFAT, PEMD: Carcass Category EBVs need to have carcass ultrasound scanning linkage (LINKED_CAR)
- WFEC, PFEC: Fecal Egg Count Category EBVs need to have fecal egg count linkage (LINKED_FEC)
- NLB, NLW: Reproductive Category EBVs need reproductive linkage (LINKED_REP)
The EBV Category Criteria used provides some important context and should be kept in mind when evaluating animals against the percentile rankings.
MBWT, BWT, MWWT, WWT, PWWT, YWT and US Hair Index: Most animals included in the calculation of the percentile report would have had direct measurements for BWT, WWT and PWWT but MBWT and MWWT would only have been measured on the 2023 ewe lambs that lambed in 2024. The main component of the US Hair Index is NLW, see NLB and NLW below.
PFAT, PEMD: There is the potential for direct measurement of these two EBVs for animals included in the calculation of the percentile bands (2023 and 2024 born) but a very small number of animals have linkage for carcass traits and a smaller number of animals are actually scanned. This is even evident in the percentile bands; the 50th and 60th percentile bands are zero, mostly because of animals with accuracies that are too low.
WFEC, PFEC: There is the potential for direct measurement of these two EBVs for animals included in the calculation of the percentile bands (2023 and 2024 born). But, not all animals included in the calculation were directly measured.
NLB, NLW: Only ewe lambs born in 2023 that lambed in 2024 could be directly measured for NLB and NLW. About 18% of the 2023 born ewes lambed in 2024. The percentile bands are calculated using male and female animals born in 2023 or 2024, but only about 5.5% of them with direct measurements (2023 ewes that lambed). Rams will only have measurements (indirect from their daughters) when their daughters start lambing.
Misconceptions
There are many misconceptions when it comes to what data is included in the percentile calculations for various traits.
Only animals that are fecal egg count tested are included in the WFEC and PFEC percentile calculations: This is not the case; an animal does not have to be fecal egg count tested to be included in the percentile calculation for WFEC and PFEC. Over 40% of the animals included in the percentile calculation for WFEC and PFEC did not have a fecal egg count tested.
A minimum accuracy is required for EBV values to be used in the percentile calculation: This is not the case; breed, year born, status and linkage is the only filter. About 2.7% of the animals included in the percentile calculation for NLB had 0 accuracy.
Animals must have EBVs to be included in the percentile calculation: Same as the previous answer. Because zero accuracy values are included you will also get that zero EBVs values are included in the calculation. These zero values are not true zero, they are zero because no EBV value is provided for the animal. For the calculation of percentile values for WFEC there are just over 11% of the animals that have zero values because they do not have sufficient accuracy to receive EBVs.
While this might all seem confusing, don’t be confused. With the misconceptions out of the way, we can simply state what data is used to calculate percentile values:
- Katahdin sheep
- Born the last two years (2023 or 2024 in this case)
- STATUS of “CURRENT” or “SOLD”
- Linkage for the appropriate category (or stated another way, eligible for across-flock EBVs)
Exploring Percentile Data
It can be informative to view the percentile data in visual format. The following charts display a “percentogram-like” chart for various traits.
How to read the chart:
- The x-axis at the bottom has a scale of values for the EBV
- The x-axis at the top has a scale of percentile values spaces according to EBV value
- The colored bars show the range of percentile bands in increments of 10. Each colored bar represents the same number of animals, narrow bands are denser because they represent 10% of animals for a small increment of EBV value. Wide bands (e.g. from the 90th to the 100th percentile for NLB) are less dense because they represent 10% of animals for a large increment of EBV value.
- The smooth line chart displays the density (the higher the line, the more dense, the lower the line the less dense).
- The dotted red vertical line shows where the mean is for this EBV.
NLB
Below is the chart for NLB values that are included in the percentile calculation for NLB percentile values.
Observations:
- Mostly normal distribution like you would expect
- There is a bit of an anomaly where NLB is zero, that is because of the inclusion of animals that do not have NLB EBVs in the calculation of percentile values
- The mean is not far from the median (50th percentile)
- The left and right tails are less dense as would be expected
WWT
Below is the chart for WWT values that are included in the percentile calculation for WWT percentile values.
Observations:
- Mostly normal distribution like you would expect
- There is a bit of an anomaly where WWT is zero but a lot smaller than for NLB, that is because of the inclusion of animals that do not have WWT EBVs in the calculation of percentile values
- The mean is not far from the median (50th percentile)
- The left and right tails are less dense as would be expected
WFEC
Below is the chart for WFEC values that are included in the percentile calculation for WFEC percentile values.
Observations:
- WFEC is limited on the left to -100
- Large anomaly where WFEC is zero, that is because of the relatively large number of animals with no WFEC that is included in the percentile calculation for WFEC
- The mean is not far from the median (50th percentile)
- The tail on the right goes out a long way
MWWT
MWWT percentile also has a large influence from the animals that do not have MWWT EBVs but are included in the percentile calculation as can be seen in the chart below.
US Hair Index
PEMD
PEMD percentile is totally dominated by animals with zero values for PEMD as can be seen in the chart below.
Conclusion
The Percentile Report provides a mechanism for you to put individual EBVs in context. The context is built from data of the animals that have been born the last two years. The data used comes from animals that represent the latest potential of genetics available, not necessarily the best tested genetics. When comparing tested and untested animals using the Percentile Report you must also include accuracy in the comparison; the Percentile Report produces the scale and you need to make your own value judgement when it comes to accuracy.
Knowing what percentile means, what data is used to calculate the percentile bands for various EBVs, and knowing how to look up percentile values allows you to more effectively evaluate animals, plan, market and sell to customers. Percentile and where an animal ranks on the percentile provide a language that people not familiar with EBVs can relate to.
By: Etienne Richards, Gibraltar Farm, EAPK Member
