Alaska COVID-19 projection

The following information is from the Alaska Department of Health and Social Services COVID-19 website: This graph represents the daily COVID-19 case count in Alaska (yellow). Date of symptom onset was used. Gray bars represent data from the most recent 7 days, which was not included in the analysis due to incomplete data/delay in reporting. The blue dotted line represents the predicted daily case trajectory (assumed exponential), with the gray band representing the 95% Confidence Interval (estimate range) of the projection. For a complete description of the methods please view the Methods tab.

Projection statistics:

The modeled exponential trajectory can be one of growth (getting bigger) or decay (getting smaller). If in growth, the doubling time represents the projected amount of time it will take for the counts to double in size. This assumes a constant growth rate (r) from the observed data under an exponential trajectory. If in decline, the halving time represents the projected amount of time it will take for the counts to reduce in half. This also assumes a constant halving rate (r) from the observed data under an exponential trajectory. The 95% confidence intervals (CI) for these estimates are also provided.

Confidence intervals (CI) provide an indication of precision of an estimated parameter. Specifically, a 95% CI means that if we sampled the same population an infinite number of times, the generated CI's for each sample would contain the true population parameter in 95% of the cases, assuming no systematic (bias) error. Generally speaking however, we can interpret the CI as a range around a point estimate within which the true value is likely to lie with a specified degree of probability, assuming there is no systematic error (bias or confounding). If the sample size is small and subject to more random error, then the estimate will not be as precise, and the confidence interval would be wide, indicating a greater amount of random error. In contrast, with a large sample size, the width of the confidence interval is narrower, indicating less random error and greater precision. One can, therefore, use the width of confidence intervals to indicate the amount of random error in an estimate.

Updated 5:43 p.m.: Alaska gained 50 new confirmed cases of COVID-19 in the latest announcement from the Alaska Department of Health and Social Services.

Of the new cases, 39 are of Alaska residents, pushing the resident total above 1,000 for the first time, to a total of 1,017.

Eleven nonresident cases were also announced Thursday, afflicting individuals in eight boroughs and census areas and raising the nonresident case count to 209.

Two of the new resident cases are of people from the Fairbanks North Star Borough, raising the total number of cases confirmed in among borough residents to 149 since the outbreak began in March. None of the new nonresident cases are from within the Fairbanks borough.

The 39 new resident cases come from 13 communities: Anchorage, 13 cases; Wasilla, nine; Palmer, four; Seward, three; Tok, two; and one each in Big Lake, Chugiak, Kenai Peninsula North, Eagle River, Fairbanks, Kodiak, North Pole and Sitka.

The combined 50 new cases announced Thursday, which cover the 24-period ending at 11:59 p.m. Wednesday, continue a trend of higher case counts. Monday and Tuesday saw combined resident and nonresident case counts of 47 and 42, for a three-day total of 139 cases.

The department projects the upward trend will continue, though the projections vary for each date depending on given data confidence levels.

Dr. Anne Zink, the state's chief medical officer, in a tweet Thursday urged Alaskans to be safe outside.

"We live in the greatest playground in the world — enjoy the state in your family bubbles. If you do choose to go to a public space, please do it safely," she wrote.

Cases began rising in late May when the state began relaxing the restrictions that had been put in place to control the spread of the virus.

Of the 1,017 resident cases, 535 people have recovered and 14 have died, including some who died out of state. That leaves the state with 46% of its total cases classified as active.

Contact Editor Rod Boyce at 459-7585. Follow him on Twitter: @FDNMeditor