NOWDx Test for the Detection of Antibodies to COVID-19: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for NOWDx Test for the Detection of Antibodies to COVID-19 (NCT04690413), a na na study. The primary outcome is Percentage of Clinical Agreement Between NOWDx COVID-19 Test and Emergency Use Authorized or FDA Cleared Comparator..

2. Clinical Question

The clinical question is one of agreement between two types of test result, not whether assignment to the device changes a health outcome. The NOWDx test detects antibodies, while the comparator is a PCR test result. These tests measure different biological targets, so agreement describes how their classifications correspond in the studied setting; it does not make them interchangeable measures. The record's stated intent is to compare device performance with a marketed test, but it does not report a conclusion about comparability.

The registry lists an enrollment of 129. That figure describes enrollment, not necessarily the number contributing to the primary outcome: the analysis population and the number with paired, interpretable test results are not reported in the registry record. The record also does not report the timing of blood collection relative to the prior PCR result or provide further details about how participants with prior positive and negative results were distributed. Those details matter when interpreting agreement, because the composition and timing of the tested population can affect the observed correspondence between results.

3. Trial Design

The registry describes a completed, single-group study of the NOWDx COVID-19 Test. The listed allocation is NA, and masking is listed as none. The design is therefore not a randomized comparison between treatment arms. The record describes people tested with the investigational device who had previously tested positive or negative using an emergency use authorized or FDA cleared COVID-19 test. That earlier PCR result serves as the comparator for assessing agreement.

The stated study intent was to compare NOWDx performance with an emergency use authorized PCR test result and to assess whether the rapid test device was comparable to a currently marketed device. The primary outcome description also permits an emergency use authorized or FDA cleared PCR comparator. The registry does not describe how a particular comparator was selected, how much time elapsed between the PCR test and the NOWDx test, or whether comparator results were verified or adjudicated.

The study record gives a start date of 2020-09-01 and a primary completion date of 2020-12-31, and lists the status as COMPLETED. It lists enrollment as 129. The study phase is NA. A sample-size justification, protocol-based power calculation, and detailed analysis plan are not reported in the registry record. The record lists one primary outcome measure and zero analyses.

Because the study is single-group and nonrandomized, it does not estimate a randomized treatment effect. Its central statistical task is to characterize agreement between the NOWDx result and the earlier PCR classification. The comparison may be informative about observed classification correspondence in the enrolled group, but the record does not establish that the enrolled group represents a broader population. Nor does the design, as described, separate test performance from possible differences in timing, participant selection, or the conditions under which the two tests were performed.

The registry identifies NOWDiagnostics, Inc. as sponsor. Additional details about recruitment, test operators, sample handling, blinding of result interpretation, and participant flow are not reported in the registry record. Without those details, the design can be described at the level of its stated single-group structure and intended agreement assessment, but not reconstructed in greater operational detail.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Overall Study

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Percentage of Clinical Agreement Between NOWDx COVID-19 Test and Emergency Use Authorized or FDA Cleared Comparator., measured over 1 day.

The primary outcome is the percentage of results matching the PCR comparator, assessed over a timeframe of 1 day. Its description calls for calculating positive percent agreement (PPA) and negative percent agreement (NPA) between the NOWDx COVID-19 Test and an emergency use authorized or FDA cleared COVID-19 PCR test. PPA concerns agreement among results classified as positive by the comparator; NPA concerns agreement among results classified as negative by the comparator. These measures describe concordance in each comparator category rather than a single overall agreement value.

Separate agreement measures are useful because a test may correspond differently with comparator-positive and comparator-negative results. Reporting both can make that pattern clearer than one combined percentage. The measures are framed as agreement with PCR, not as sensitivity and specificity against a definitive reference standard. The registry record does not establish that the PCR result is a perfect measure of infection status, and the tests target different analytes: the NOWDx device is intended to detect total antibodies, whereas PCR detects viral genetic material.

The stated timeframe is 1 day, but the registry record does not explain how that timeframe relates to the prior PCR test, specimen collection, or result availability. It also does not report the numerator or denominator for either agreement measure, the resulting PPA or NPA, confidence intervals, or a prespecified threshold for what would count as comparable performance. Without the underlying paired classifications and estimates, the endpoint's intended meaning can be described, but the observed level and precision of agreement cannot be evaluated.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

Agreement analysis compares classifications made by two tests on the same participants. For this study, the intended comparison is between NOWDx results and prior PCR results. The primary outcome description calls for separate positive percent agreement and negative percent agreement. In general, separate measures matter because the proportion of matching results can differ depending on whether the comparator classifies a result as positive or negative. Neither measure can be calculated or interpreted from enrollment alone; each requires the paired classifications and the relevant comparator-category denominator.

What do PPA and NPA express?

In general, PPA is the proportion of comparator-positive results that are also positive on the test being evaluated. NPA is the proportion of comparator-negative results that are also negative on the test being evaluated. Both express agreement conditional on the comparator category. They are not, by themselves, direct estimates of the probability that a person truly has or does not have a condition. Such interpretations would require a reference standard and assumptions about how well it identifies the underlying state. The registry describes PCR as the comparator and does not establish it as an error-free reference standard.

For this trial, the distinction is especially relevant because the NOWDx test is described as a qualitative antibody test, while the comparator is PCR. Antibody detection and PCR detection concern different targets. In general, test results aimed at different targets may not correspond perfectly, and timing can influence the relationship between them. The registry gives a timeframe of 1 day for the primary outcome but does not explain the timing between the NOWDx test and the earlier PCR result. A reader therefore cannot use the timeframe alone to determine the interval between tests or to interpret discordant results.

Why do denominators matter?

Each agreement estimate depends on the number of participants with the corresponding comparator classification and an evaluable NOWDx result. The total enrollment is 129, but the record does not say how many participants contributed paired results or how many were in either comparator category. It also does not report excluded, indeterminate, or missing results. These absent details prevent assessment of whether the analysis included all enrolled participants or only a subset. In general, exclusions and missing paired results can affect both the estimate and its generalizability, particularly if unavailable results are not unrelated to test classification.

A confidence interval is a statistical expression of uncertainty around an estimate. In general, a narrower interval indicates greater precision under the method's assumptions, while a wider interval indicates more uncertainty. Interval width depends in part on the number of informative observations and on the observed pattern of agreement. No intervals or outcome counts are reported in the registry record, so neither the precision nor the stability of PPA and NPA can be assessed. The record also does not identify the interval method.

What can a hypothesis test establish?

A hypothesis test evaluates data against a defined null hypothesis. It can address a specific question, but does not substitute for an effect estimate or its confidence interval. A claim of equivalence or noninferiority ordinarily needs a prespecified margin and an analysis suited to that objective. Here, the registry describes an intent to show comparability but does not report a margin, formal hypothesis, analysis method, test statistic, or p-value. The stated intention therefore cannot be read as evidence that a formal criterion for comparability was satisfied.

The record lists zero analyses. That means no analysis results are described in the registry entry; it does not reveal whether analyses were conducted outside the record. The protocol, statistical analysis plan, handling of missing or indeterminate outcomes, and any prespecified subgroup analyses are not reported in the registry record. Without these materials or posted numerical results, the planned methods cannot be reconstructed.

How should planning calculations be read?

In general, sample-size planning calculations ask how many observations a hypothetical design might require under stated assumptions. They are not observed outcomes and do not establish the precision achieved in a completed study. The planning assumptions associated with this record describe a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation, with the effect to detect expressed as a stated fraction of an observed effect. For time-to-event calculations, the stated convention is total events using the Schoenfeld approach; other calculations are expressed as participants per arm.

Those assumptions describe an illustrative two-arm planning framework, whereas the registry describes this study as single-group, with allocation listed as NA. No planning results or observed effect estimates are reported in the registry record. Such calculations should not be mistaken for the study's own design justification, nor for observed power after study completion. A sample-size justification and the study's own statistical plan are not reported in the registry record.

Finally, safety counts and agreement estimates answer different questions. Adverse-event counts describe events recorded in a safety group; PPA and NPA describe paired test classifications. In general, a zero event count does not establish that an event is impossible, and its interpretation depends on follow-up, ascertainment, and the population at risk. The registry does not report further safety-analysis methods or follow-up detail. The reported safety entries should therefore be read as descriptive registry counts, not as a replacement for the absent agreement analysis.

10. Multiplicity, Missing Data and Analysis Populations

The primary outcome description identifies PPA and NPA, which are separate agreement measures. The registry does not explain whether these were treated as co-primary outcomes, whether one was primary and the other supportive, or whether any decision rule required both to meet a criterion. It reports no multiplicity adjustment, hierarchy, or other procedure for handling multiple statistical questions. Such procedures are not necessarily required for every descriptive analysis, but their presence or absence can matter when several inferential claims are made. The registry record does not report the relevant analysis plan.

Missing-data handling is also not described. The record does not state how participants without paired test results, uninterpretable results, or unavailable comparator results were handled. It does not report the number of such records or whether any imputation or sensitivity analysis was used. These details are important because agreement calculations require paired classifications, and the included population can differ from the enrolled group. Enrollment is listed as 129, but the primary-outcome analysis population is not reported in the registry record.

The record does not define an analysis population such as all enrolled participants or all participants with evaluable paired results. It also does not describe exclusions or protocol deviations. The fact that the registry lists zero analyses means outcome analyses are not reported in the entry; it does not establish what analyses may have been conducted elsewhere. The protocol and statistical analysis plan are not reported in the registry record, so prespecification and deviations from a planned analysis cannot be assessed.

Accordingly, neither multiplicity control nor missing-data assumptions can be evaluated. No inference about their adequacy should be drawn from the stated study objective alone.

11. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

The registry lists the investigational-device group as having 124 at risk for serious adverse events and 0 serious adverse events. It also lists 124 at risk for other adverse events and 0 other adverse events, with 0 deaths. These are the recorded figures for the safety group described in the registry. They are not the sample sizes or results for the primary agreement outcome, and the record does not establish that the safety and outcome-analysis populations were identical.

A zero recorded event count means that no events of that category are listed in this registry entry for the stated group. In general, it does not demonstrate that an event cannot occur or that risk is absent. Interpretation depends on how events were sought, the duration and completeness of follow-up, and which participants were included. Those details are not reported in the registry record. The record also does not list serious adverse-event terms.

The figures should therefore be read as descriptive safety reporting, not as a comparative safety estimate. This is a single-group study, and no randomized control group is described. The registry entries do not permit a relative safety comparison or broader conclusion about event risk.

12. What the Result Does, and Does Not, Mean

The registry record makes clear what the study set out to assess: agreement between NOWDx antibody-test results and prior PCR classifications, expressed through PPA and NPA. It also documents a single-group design, an enrollment of 129, a timeframe of 1 day for the primary outcome, and completion status. These details help define the intended question and the study's basic structure.

The record does not report the PPA or NPA estimates, paired-result counts, confidence intervals, or analysis population. It therefore does not establish how much agreement was observed or how precisely it was estimated. Nor does it report a formal comparability criterion or demonstrate that such a criterion was met. The study's stated intent to show comparability should not be confused with a finding of comparability.

Even with numerical agreement results, these measures would describe correspondence with the PCR comparator rather than necessarily identifying true disease status. The tests target different analytes: NOWDx is intended to detect total antibodies, while PCR is the stated comparator. The registry does not report the interval between tests or further timing details, which limits interpretation of discordant classifications. Agreement alone would not establish clinical utility, performance in other settings, or outcomes beyond the tested group.

The safety record lists zero serious adverse events, zero other adverse events, and zero deaths among the listed group, with 124 at risk for each adverse-event category. These entries are descriptive and do not show the absence of all possible harms or provide a comparative safety assessment. Further details about ascertainment and follow-up are not reported in the registry record.

The appropriate conclusion is bounded: the registry documents an intended diagnostic agreement evaluation, but does not contain the numerical analysis needed to judge the observed agreement. It also does not support claims about equivalence, broader performance, or certainty beyond the recorded study description.

13. Why This Trial Matters Statistically

Agreement studies address a practical statistical problem: whether classifications from a test under evaluation correspond to those from a comparator in a defined study population. Reporting positive and negative agreement separately can reveal whether correspondence varies across comparator classifications. That distinction is relevant to how readers understand diagnostic data, because one overall percentage could obscure different patterns in the positive and negative groups.

This study also illustrates why the comparator and the target of each test need to be stated clearly. The NOWDx device is intended to detect total antibodies to SARS-CoV-2, while the comparator is a PCR result. Agreement between them is not automatically equivalent to accuracy against a definitive reference standard. The distinction helps prevent a statistical measure of correspondence from being interpreted as a broader claim about truth or clinical performance.

Design structure matters as well. The record describes a single-group study with no allocation and no masking, rather than a randomized comparison. That structure suits a stated agreement objective, but it does not create a concurrent randomized control group or resolve possible effects of selection, timing, and test administration. Statistical interpretation depends on those design features as well as the choice of summary measure.

Finally, this record demonstrates why numerical results and uncertainty estimates are essential. Naming an endpoint does not show what value was observed, how many paired observations informed it, or how precise it was. The registry lists the intended outcome but zero analyses. Keeping the distinction between a study objective and its reported evidence clear is central to responsible interpretation.

14. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The most consequential limitation of the registry entry is that it reports no primary-outcome analysis. Although PPA and NPA are specified, no estimates, denominators, paired classifications, or confidence intervals are reported in the registry record. The entry therefore cannot support a quantitative assessment of agreement or precision.

The analysis population and participant flow are also not described. Enrollment is listed as 129, while the safety group has 124 at risk; the registry does not explain this difference, and it would be inappropriate to infer its cause or treat either figure as the primary-outcome denominator. The number of participants with both a NOWDx result and an evaluable PCR comparator is not reported.

Important operational details are absent. The record does not report the interval between the prior PCR test and NOWDx testing, the selection of the comparator within the stated categories, procedures for handling indeterminate results, or whether test interpretation was blinded. It also does not describe participant characteristics or recruitment methods. These omissions limit assessment of selection, timing, and generalizability.

The stated objective concerns comparability, but a comparability margin and formal equivalence or noninferiority analysis are not reported. A statistical analysis plan, missing-data methods, multiplicity approach, and sample-size justification are also not reported in the registry record. Finally, the single-group design does not provide a randomized control group. The record supports description of the intended agreement evaluation, but not a complete appraisal of its conduct or results.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: NOWDx Test for the Detection of Antibodies to COVID-19 — NCT04690413.
• Registry record last updated 2024-03-01; status last verified 2022-10.
• Results first posted 2022-10-28.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

18. Record Summary

The registry record identifies NCT04690413 as a completed, single-group study of the NOWDx COVID-19 Test for detection of antibodies to COVID-19. The listed enrollment is 129. The study start date is 2020-09-01, and the primary completion date is 2020-12-31. Allocation is listed as NA, masking as none, and phase as NA.

The primary outcome is percentage of results matching an emergency use authorized or FDA cleared PCR comparator, with PPA and NPA specified over a timeframe of 1 day. The record lists one outcome measure and zero analyses. Numerical agreement results and their precision are not reported in the registry record.

For the investigational-device group, the safety entries list 124 at risk for serious adverse events and 0 serious adverse events; the other-adverse-event entries list 124 at risk and 0 affected, with 0 deaths. The registry does not report further details needed to interpret agreement results, analysis populations, missing data, or safety follow-up.