Patient identifiers and storage at a rural clinic
A rural health clinic in Kavango East serves about 7,600 active patients and keeps one paper folder per patient. The clinic has a single desktop computer and a 32 GB USB flash drive for backups. Staff want to replace paper folders with scanned images and give every patient a numeric identifier printed as a barcode. The current identifier uses four decimal digits and is typed into a spreadsheet when a patient visits. The clinic expects the number of active patients to grow by about 8% each year. A scanned page is about 250 KB, and an average folder contains 14 pages. Staff also want to use the identifier on handwritten forms, where digits are sometimes misread, for example 6 and 8, or 1 and 7. The clinic cannot afford a new server this year but can buy one external hard drive or pay for a small cloud account. It must keep records for at least five years.
1. Calculate the largest number of patients that a four-digit decimal identifier can represent, and estimate when the clinic will run out of identifiers at 8% annual growth. Recommend a practical identifier length and justify it.
Read the worked answer
Four decimal digits with leading zeros give 0000 to 9999, i.e. 10,000 possible identifiers. Active patients: 7,600 × 1.08 = 8,208; × 1.08 = 8,865; × 1.08 = 9,574; × 1.08 = 10,340. So the clinic exceeds 10,000 during the fourth year, even before counting inactive patients whose numbers must not be reused. The four-digit system is therefore not safe for a five-year record. A five-digit code (100,000 values) would last far longer, but a six-digit code is more practical: it allows a check digit plus a branch or year code, and six digits are easier to print as a barcode at a usable width. The recommendation should be six digits with one check digit, not simply the shortest code that fits today. Capacity alone is not the only criterion: identifiers must remain unique permanently and must survive handwriting and barcode errors.
2. Estimate the storage needed to scan all 7,600 folders at 250 KB per page and 14 pages per folder. Decide whether the 32 GB USB drive is adequate for the scans plus two backup copies, showing your working.
Read the worked answer
Pages = 7,600 × 14 = 106,400. At 250 KB per page, raw storage = 106,400 × 250 KB = 26,600,000 KB. Divide by 1,024 twice: 26,600,000 / 1,024 = 25,976.6 MB; /1,024 = 25.37 GB (about 25.4 GB). Add 20% for index, temporary files and wasted space: 25.37 × 1.20 = 30.45 GB. A nominal 32 GB USB drive is usually about 29.8 GiB usable, so one copy may not fit with overhead, and it is far too small for the scans plus two backup copies (about 91 GB). The USB drive is also a single point of failure and easy to lose. Recommend an external hard drive of at least 250 GB, or a cloud account with versioning, and keep one copy off-site. Compressing scans to 80–100 KB per page would reduce the load but should not be the only safeguard.
3. The clinic wants a check digit on patient identifiers. Explain how a simple check digit works and why it is more suitable than a single parity bit for typed or handwritten digits.
Read the worked answer
A check digit is an extra digit calculated from the other digits and appended to the identifier. For example, with a simple modulus-11 scheme, multiply digits by weights 1,2,3..., add, divide by 11, and use the remainder (with a rule for 10). When the number is typed or scanned, the system recalculates and compares. It catches most single-digit errors and many transpositions such as 12 typed as 21. A single parity bit works on binary data: it makes the number of 1 bits odd or even and detects an odd number of bit errors. It does not understand decimal digits, cannot catch a swap of two digits that preserves parity, and gives no useful message to a clerk. For handwritten and typed identifiers, a decimal check digit is more suitable, and a barcode can carry the same check digit so the scanner and the database both validate it.