Browsing by Author "Muller, C."
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- ItemThe elimination of errors caused by prior technetium-99m scintigraphy on iodine-131 thyroid uptake measurements.(Health & Medical Publishing Group, 1987) Wasserman, H. J.; Muller, C.; Klopper, J. F.Coincidence summing of technetium-99m (99mTc) pulses may disturb iodine-131 (131I) thyroid uptake measurements if these are obtained after 99mTc thyroid scintigraphy performed on the same day. The magnitude of the error was assessed in 26 patients. It was found that when pre-dose measurements were subtracted, the 6-hour and 24-hour 131I uptakes could be falsely decreased by up to 137 percentage points using a lower discriminator level of 250 keV and by up to 35 percentage points with a discriminator level of 300 keV. When pre-dose measurements from 99mTc were ignored, there was a general increase in 131I uptake values at 6 hours. Increases of up to 22 and 9 percentage points occurred when 250 keV and 300 keV lower discriminator levels respectively were used. These errors may be eliminated by performing 131I uptake measurements through a 1 mm lead filter.
- ItemMarket reaction to tender and private offers on the JSE(AOSIS, 2017) Wesson, N.; Muller, C.; Ward, M.Investors can benefit when incorporating the information-signalling effect of share repurchases in their investment strategies. Previous South African studies on open market share repurchases confirmed the globally observed signalling-effect, but found open market share repurchases not to be the outright favoured share repurchase type in this country – as is the case globally. The present study is the first to examine the market reaction to the preferred share repurchase type, namely specific (or tender and private offers) share repurchases, in the South African regulatory environment. Abnormal returns were calculated using a 12-parameter benchmark over a four-year event window, for share repurchases announced from 1999 to 2009. Pro rata tender offers were found not to possess information-signalling benefits, but significant excess returns subsequent to the announcement date were reported for the two private offer types (namely other specific offers and the repurchase by the holding company of shares held by subsidiaries). The other specific offers were found to possess significant information-signalling benefits – especially over the long term and in respect of value companies.
- ItemMarket underreaction to open market share repurchases on the JSE(AOSIS, 2014) Wesson, N.; Muller, C.; Ward, M.This study examined the long-term performance of open market share repurchase announcements made by companies listed on the JSE during their reporting periods including 1 July 1999 to 2009. A total of 195 open market share repurchase announcements were identified. A maximum outperformance of about 35% was found on day t+550 (about two years subsequent to the announcement). After splitting the sample into 'value' (low P/E ratio) and 'growth' shares (high P/E ratio), it was found that the outperformance was almost entirely confined to the value portfolio, reaching a maximum of about 80% by day t+630 (about two-and-a-halfyears subsequent to the announcement). This study applied a more robust research methodology than used in earlier South African research on this topic; it also used an improved dataset and extended the research period, compared to other research. The results of this study showed much higher positive abnormal returns than were found in earlier international and South African studies. Investors should take advantage of the informational value of open market repurchase announcements and the related significant abnormal returns to be earned.
- ItemMathematical models and the fight against diseases in Africa(Academy of Science for South Africa, 2003) Getz, W. M.; Gouws, E.; Hahne, F.; Kopp, P. E.; Mostert, P.; Muller, C.; Seioghe, C.; Williams, B.; Witten, G.; Bradshaw, D.; Dorrington, R.A new initiative proposes to build capacity across Africa to collect data and conduct quantitative analyses necessary to understand the dynamics of major diseases afflicting the continent, with an initial emphasis on HIV/AIDS.